Delaware Bay Shorebird-Horseshoe Crab 

Assessment Report and Peer Review

Prepared for the 

 Atlantic States Marine Fisheries Commission 

 by the 

 U.S. Fish and Wildlife Service 

 Shorebird Technical Committee 

 Peer Review Panel 

 June 2003 
Information in the report was compiled by Brad A. Andres and available from U. S. Fish and 

Wildlife Service, Division of Migratory Bird Management, 4401 N. Fairfax Dr., MBSP 4107, 

Arlington, VA, 22203, USA or at http://migratorybirds.fws.gov/reports/reports.html 

Report authors are listed in the Literature Cited. Some sections were drafted by Nellie Tsipoura 

(Rutgers University), Joanna Burger (Rutgers University), Gregory Breese (U. S. Fish and 

Wildlife Service), and Kimberly Cole (Delaware Coastal Management Programs). Shorebird 

Technical Committee members provided review. 

Suggested citation: U.S. Fish and Wildlife Service. 2003. Delaware Bay Shorebird-Horseshoe 

Crab Assessment Report and Peer Review. U.S. Fish and Wildlife Service Migratory Bird 

Publication R9-03/02. Arlington, VA. 99 p. 
TABLE OF CONTENTS

A. Conclusions, Recommendations, and Peer Review..............................................1 

1.0. PURPOSE AND APPROACH....................................................................................1 

2.0. LONG-DISTANCE MIGRATION IN SHOREBIRDS ..............................................1 

3.0. CONCLUSIONS..........................................................................................................2 

3.1. Shorebird Use of Delaware Bay ......................................................................2 

3.2. Shorebird Population Trends ...........................................................................2 

3.3. Shorebird Population Threats ..........................................................................3 

3.4. Shorebird Use of Horseshoe Crab Eggs...........................................................4 

3.5. Availability of Horseshoe Crab Eggs ..............................................................4 

3.6. Shorebird Weight Gain in Delaware Bay ........................................................5 

3.7. Shorebird Survival ...........................................................................................6 

4.0. RECOMMENDATIONS.............................................................................................7 

4.1. Direct Management..........................................................................................8 

4.1.1. Horseshoe crab egg abundance.........................................................8 

4.1.2. Seasonal beach closures....................................................................8 

4.1.3. Habitat protection and enhancement.................................................8 

4.3. Needed Analyses............................................................................................10 

4.2.1. Horseshoe crab egg abundance.........................................................9 

4.2.2. Shorebird breeding-ground conditions .............................................9 

4.2.3. Shorebird diet and energetics............................................................9 

4.3. Improved Monitoring and Research ..............................................................10 

4.3.1. Bay-wide horseshoe crab egg abundance .......................................10 

4.3.2. Shorebird population surveys .........................................................10 

4.3.2. Individually-marked shorebirds......................................................10 

4.3.4. Measurements of weight gain .........................................................10 

4.3.5. Southern stop over quality ..............................................................10 

5.0. SHOREBIRD TECHNICAL COMMITTEE MEMBERSHIP .................................11 

6.0. PEER REVIEW PANEL PARTICIPANTS ..............................................................11 

B. Shorebird-Horseshoe Crab Assessment .............................................................12 

1.0. INTRODUCTION .................................................................................................................12 

1.1. Shorebird Technical Committee ....................................................................12 

1.2. Horseshoe Crabs, Shorebirds, and Delaware Bay .........................................12 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 ii 

1.3. Economic Value of Crabs and Shorebirds.....................................................13 

1.4. Evaluation Approach .....................................................................................13 

2.0. DELAWARE BAY SHOREBIRDS..........................................................................14 

2.1. Species Considered ........................................................................................14 

2.2. Conservation Status and Protection ...............................................................14 

2.3. Vulnerability of Long-distance Migrant Shorebirds and the Red Knot Focus15 

2.4. Red Knot Distribution....................................................................................15 

2.5. Red Knot Annual Cycle.................................................................................15 

2.6. Distribution and Migration Routes of Other Species.....................................16 

2.6.1. Ruddy turnstone..............................................................................16 

2.6.2. Sanderling .......................................................................................17 

2.6.3. Semipalmated sandpiper .................................................................17 

2.6.4. Dunlin .............................................................................................17 

2.6.5. Short-billed dowitcher ....................................................................17 

2.6.6. Long-billed dowitcher.....................................................................18 

2.6.7. Least sandpiper ...............................................................................18 

3.0. ABUNDANCE AND DISTRIBUTION OF HORSESHOE CRABS.......................18 

4.0. POTENTIAL THREATS TO SHOREBIRDS ..........................................................20 

4.1. Heavy Metal Concentrations in Shorebirds and Horseshoe Crabs ................20 

4.2. Organic Compound Concentrations in Shorebirds and Horseshoe Crabs .....21 

4.3. Disease in Shorebirds.....................................................................................22 

4.4. Shoreline Changes in Delaware Bay..............................................................23 

4.5. Sea Level Rise from Global Climate Change................................................23 

4.6. Arctic Breeding Ground Conditions ..............................................................23 

4.7. South American Wintering Ground Conditions ............................................25 

4.8. Human Disturbance to Shorebirds.................................................................25 

4.9. Effect of Disturbance on Survival of Semipalmated Sandpipers...................26 

4.10. Horseshoe Crab Bait Landings ....................................................................27 

4.11. Changes in Horseshoe Crab Populations .....................................................27 

5.0. ESTIMATES OF SHOREBIRD POPULATION SIZES AND TRENDS................29 

5.1. Shorebird Population Sizes............................................................................29 

5.1.1. Coarse continental estimates...........................................................29 

5.1.2. Re-sighting banded red knots in the 1980s.....................................29 

5.1.3. Red knot band re-sighting in South America..................................30 

5.2. Shorebird Population Trends .........................................................................30 

5.2.1. Aerial surveys of red knots in South America................................30 

5.2.2. Spring aerial surveys in Delaware Bay...........................................31 

5.2.3. International and Maritime Shorebird Surveys...............................32 

5.2.4. Quebec migration checklists...........................................................32 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 iii 

6.0. IMPORTANCE OF DELAWARE BAY TO SHOREBIRD POPULATIONS ........33 

7.0. HABITAT USE BY SHOREBIRDS AND HORSESHOE CRABS.........................34 

7.1. Shorebird Use of Marine and Non-marine Habitats ......................................34 

7.2. Red Knot Habitat Use and Movements in Delaware Bay..............................34 

7.3. Shorebird Habitat Use on Cape May Peninsula, New Jersey ........................34 

7.4. Shorebird Beach Use in Delaware .................................................................35 

7.5. Influence of Beach Characteristics on Horseshoe Crab Reproductive Activity35 

7.6. Beach Nourishment and Habitat Restoration for Crabs and Shorebirds .......36 

7.7. Shorebird Habitat Use in Relation to Beach Characteristics and Abundance 

of Horseshoe Crabs and Their Eggs...........................................................37 

8.0. ABUNDANCE AND TRENDS OF HORSESHOE CRAB EGGS ..........................38 

8.1. Bay-wide Egg Density in 1999......................................................................38 

8.2. Egg Density on Delaware Beaches................................................................38 

8.3. Changes in Egg Density on New Jersey Beaches..........................................38 

8.4. Egg Abundance Sampling Design Considerations ........................................39 

9.0. SHOREBIRD DIET AND USE OF HORSESHOE CRAB EGGS...........................39 

9.1. Shorebird Diet in Delaware Bay....................................................................39 

9.2. Stable Isotope Analysis Confirms Shorebird Dependance on Horseshoe Crab 

Eggs in Delaware Bay................................................................................40 

9.3. Functional Responses of Shorebirds Feeding on Horseshoe Crab Eggs .......40 

9.4. Competition Between Shorebirds and Gulls for Horseshoe Crab Eggs ........41 

9.5. Red Knots Use of Food Other than Horseshoe Crab Eggs ............................42 

10.0 ENERGETIC REQUIREMENTS OF MIGRANT SHOREBIRDS.........................43 

10.1. An Energetics Framework for Migrant Shorebirds .....................................43 

10.2. Energetics of Sanderlings Migrating to Four Latitudes...............................44 

10.3. Predicting Flight Ranges..............................................................................44 

10.4. Fat-loading in islandica Red Knots .............................................................45 

10.5. Effects of Weight on Metabolic Power Needed for Flight .........................45 

10.6. Flight Energy Needs of rufa Red Knots Staging in Delaware Bay .............46 

10.7. Assimilation Efficiency of Sanderlings Consuming Horseshoe Crab Eggs 46 

10.8. Energy budget of Delaware Bay Shorebirds................................................47 

10.9. Horseshoe Crab Egg Requirement of Delaware Bay Shorebirds ................47 

11.0. SHOREBIRD WEIGHTS AND WEIGHT GAIN ..................................................48 

11.1. General Capture Methods ............................................................................48 

11.2. Organ Atrophy and Weight Change during Migration................................49 

11.3. Red Knot Weights through the Annual Cycle .............................................50 

11.4. Red Knot Weight Gains in Delaware Bay ...................................................51 

11.4.1. Analytical approaches...................................................................51 

11.4.2. Red knot arrival weights and weight gains...................................51 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 iv 

11.4.3. Red knot departure weights in Delaware Bay...............................53 

11.5. Weights and Weight Gain in Ruddy Turnstones and Sanderlings...............53 

11.6. Weights and Weight Gain in Semipalmated and Least Sandpipers.............54 

12.0. RED KNOT SURVIVAL AND PRODUCTIVITY................................................55 

12.1. Re-sighting Rates of Knots Banded in Florida and Argentina ....................55 

12.2. Survival Rate................................................................................................55 

12.3. Population Projections .................................................................................56 

12.4. Juvenile Age Ratios ....................................................................................56 

13.0. LITERATURE CITED ...........................................................................................57 

14.0. TABLES ..................................................................................................................72 

15.0. FIGURES.................................................................................................................91 

C. Shorebird Technical Committee Terms of Reference – 2002 ..........................94 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 1 

A. Conclusions, Recommendations, and Peer Review

1.0. PURPOSE AND APPROACH

The Atlantic States Marine Fisheries Commission asked the U. S. Fish and Wildlife Service to 

form a Shorebird Technical Committee that would provide technical guidance, regarding effects 

that horseshoe crab management actions could have on shorebird populations, to the Horseshoe 

Crab Management Board. One of the immediate tasks of the Shorebird Technical Committee 

was to produce a peer-reviewed report that synthesized unpublished and published information 

on shorebird population trends, threats to shorebird populations, shorebird habitat use, shorebird 

energetic requirements, and horseshoe crab egg abundance. Although several shorebird species 

were considered in the report, attention primarily focused on the red knot (Calidris canutus rufa). 

Available information was greatest for the red knot and was less extensive for the ruddy 

turnstone (Arenaria interpres morinella), sanderling (Calidris alba), semipalmated sandpiper 

(Calidris pusilla), and least sandpiper (Calidris minutilla). Relatively little information existed 

on the dunlin (Calidris alpina hudsonia) and short-billed dowitcher (Limnodromus griseus 

griseus). Aside from the least sandpiper, which was chosen because of its contrasting use of 

marsh habitats, all other species were selected because of their reliance on beach habitats and 

their frequency of occurrence on Delaware Bay aerial surveys (1986–2002). After reviewing the 

report, the Committee has generated this set of conclusions, management recommendations, and 

information needs. The Committee used a concordance, or preponderance, of evidence approach 

to evaluate the report’s contents. The report, conclusions, and recommendations were evaluated 

by an independent Peer Review Panel, and their comments are included here as bolded text. 

2.0. LONG-DISTANCE MIGRATION IN SHOREBIRDS

Many populations of shorebirds undertake a series of long-distance, non-stop flights to travel 

between their wintering and breeding grounds. Because a shorebird often crosses vast stretches 

of open water during migration, physiological and environmental conditions on departure can 

directly, and immediately, affect its survival. The red knot is an extreme example of the longhop migration system and has one of the longest migrations of any bird. Besides adding 50% of 

their body weight in fat reserves, red knots at Delaware Bay, and elsewhere, exhibit major 

internal organ changes in response to the need to first accumulate fat and later to reduce flight 

mass. The long-hop migration system of red knots, and other shorebird species, is highly 

dependent on food availability at a limited number of stopover sites. Failure to gain sufficient 

body mass at stopover sites, often during a short time span, can impair the health, productivity, 

and survival of migrant shorebirds. Because arctic breeding grounds are generally food limited 

in early summer when shorebirds first arrive, food-rich stopovers in the north-temperate region 

are particularly important. At these sites, shorebirds are often under relatively strict time 

constraints to add needed fat reserves. 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 2 

3.0. CONCLUSIONS

3.1. Shorebird Use of Delaware Bay

Delaware Bay has been recognized by many scientists and organizations as one of the most 

important and critical shorebird stopovers in the Western Hemisphere and, indeed, in the world. 

Depending on the species, between 12 and 80% of the Atlantic flyway population of the six 

beach-inhabiting shorebirds mentioned above (excluding least sandpiper) can be observed on 

Delaware Bay’s beaches during northward migration. Far fewer numbers of shorebirds pass 

through Delaware Bay during southward migration. For a given species, the proportion of the 

population that uses Delaware Bay each spring may vary substantially among years. Compared 

to 1986–1996, average shorebird use of Delaware Bay beaches, as measured by seasonal maxima 

of aerial survey counts, has increased or remained stable during 1997–2002 for all six beachinhabiting species. During their northward migration in the Delaware Bay region, most 

shorebird species use marine-influenced habitats — either salt marshes, tidal flats, or sand 

beaches. 

The Peer Review Panel generally agrees with these conclusions, except that a more 

sophisticated analysis of the Delaware Bay shorebird use time-series data could have been 

conducted. Data on shorebird-use days could be useful in constructing a total energy 

budget for all northward-migrating shorebirds. The importance of accessible roosting sites 

to migrant shorebirds is not mentioned.

3.2. Shorebird Population Trends

Based on a variety of sources, all available data indicate that the rufa red knot population has 

decreased since the 1980s, but the magnitude of the decline is not precisely known. Besides the 

red knot, the semipalmated sandpiper is the only other Delaware Bay shorebird species that has 

relatively consistent patterns of population decreases among trend datasets. Because of unknown 

turnover and detection rates, aerial survey data from Delaware Bay are not useful for estimating 

population sizes of shorebirds in Delaware Bay. 

The Peer Review Panel agrees that, although imperfect, patterns in the trend analyses 

reasonably indicate a decrease, of some magnitude, in populations of rufa red knots and 

semipalmated sandpipers. Most surveys of wintering and migrating red knots do not cover 

the needed range of the population and complicate interpretation of changes in populations 

at specific sites. Analytical methods used to summarize ISS data also lack rigor and may 

only reveal general patterns of population change. Current and future surveys of 

shorebird populations should undergo rigorous statistical review.
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 3 

3.3. Shorebird Population Threats

The Shorebird Technical Committee evaluated information on the potential threats to shorebird 

populations across their annual cycle. Testing for contaminants in shorebirds and crabs indicates 

that metals and pesticides are not likely causing population reductions in shorebirds. Little 

information exists on disease and parasite occurrence in red knots, particularly in Delaware Bay, 

but there is no current evidence to suggest that these are major, potential problems. Although 

environmental conditions vary considerably from year to year, arctic breeding habitats do not 

appear to have changed in ways that would likely contribute to the observed reductions in red 

knot survival and productivity. More information is needed to assess the effects that weather and 

predation in the arctic have on rufa red knot population dynamics. Arctic environmental 

conditions should also be evaluated for semipalmated sandpipers. Habitat conditions in 

wintering areas have numerous potential threats, but these are not believed to have currently 

affected key wintering sites. Food availability, however, has only been measured at a few South 

American wintering or stopover sites. Beach nourishment is not having a negative effect on 

shorebird use on Delaware beaches and is likely improving habitat quality; beach nourishment is 

not widely practiced in New Jersey. Although no Bay-specific studies have been conducted, 

repeated human disturbance likely reduces shorebird feeding efficiency in Delaware Bay. 

Elsewhere, migrant shorebirds have been disturbed by dogs, self-propelled human recreation, 

and vehicles. Human disturbance to semipalmated sandpipers feeding along the coast of 

Massachusetts as they prepared for a long over-water flight, reduced their subsequent survival. 

Gulls can potentially reduce food availability to shorebirds through direct and indirect 

competition for crab eggs. Shorebirds, however, most often forage with other shorebirds, and 

preliminary data and field observations suggest that the number of gulls using Delaware Bay 

beaches has not substantially increased in recent years. Lastly, reduced numbers of horseshoe 

crab eggs available for shorebird consumption, relative to the early 1990s, could reduce survival 

and reproductive success in the six shorebird species that use Delaware Bay as the last stopover 

prior to departing for their breeding grounds (see following sections). 

The Peer Review Panel agrees that contaminants and parasites do not currently appear to 

provide a major threat to shorebirds stopping at Delaware Bay. Further information is 

needed to thoroughly evaluate whether or not changes in habitat quality on the breeding 

and wintering grounds are contributing to declines in shorebird populations. However, 

changes in breeding or wintering area conditions do not minimize the importance of 

maintaining high quality north-temperate stopovers. Information presented in the report 

is insufficient to determine if beach nourishment generally improves habitat quality for 

spawning horseshoe crabs and foraging shorebirds. Although numerous studies have 

demonstrated the immediate, disruptive effects of human disturbance to migrant 

shorebirds, ultimate effects of disturbance on survival of shorebirds are not welldocumented and are usually inferred (including the Massachusetts semipalmated 

sandpiper study referenced above). Increases in gull numbers do not superficially appear 

to have direct or indirect influences on shorebird population changes, but more 

quantitative information on effects of interference and exploitative competition between 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 4 

gulls and shorebirds is needed. The life history of long-distance, long-hop shorebird 

migrants indicates that the availability of abundant food resources at north-temperate 

stopovers is critical for completing their annual cycle.

3.4. Shorebird Use of Horseshoe Crab Eggs

The importance of Delaware Bay as a spring shorebird stopover is likely due to the unique and 

important food resource — horseshoe crab eggs. A variety of methods (stomach analyses, 

captive feeding studies, and field observations) indicate that horseshoe crab eggs are a variable 

component in the diet of numerous invertebrates and vertebrates (shorebirds, other birds, fish, 

and turtles). Birds, and particularly shorebirds, are important predators of crab eggs. Stable 

isotope analysis indicates that red knots are highly dependent on horseshoe crab eggs. Isotope 

analysis of other shorebird species is currently underway. Red knots feed by pecking at surface 

eggs and making shallow probes into beach sediments. Captive knots fed exclusively eggs 

gained weight at rates that were similar to those observed in wild birds. Egg consumption was 

estimated at 18,000 eggs per day and rates of knot weight gain ranged from 2.6 to 8.0 grams per 

day while they were in Delaware Bay. Daily weight gains of rufa red knots in Delaware Bay are 

the highest reported for any stopover site or knot population. At other stopovers throughout the 

world, knots generally feed on molluscs or bivalves. Although Bay beaches were reported to 

have low invertebrate prey densities, detailed evidence does not exist to thoroughly evaluate 

whether or not alternative shorebird foods exist in high enough abundances to meet the energetic 

needs of red knots and other migrant shorebirds while in the Delaware Bay region. 

The Peer Review Panel believes that the importance of Delaware Bay to shorebirds is due 

to a number of factors such as an abundant primary food resource (crab eggs), the 

availability of secondary food resources, and availability of safe roost sites. Stable isotope 

analysis indicates that red knots feed almost exclusively on horseshoe crabs while at 

Delaware Bay. Although this result does not necessarily indicate a “dependency” on this 

food, crabs should be assumed to be critically important unless a viable alternative prey 

base is shown to exist. A comprehensive review of migrant shorebird foraging behavior 

and diet is needed to thoroughly evaluate the importance of Delaware Bay, and its food 

resources, to shorebirds; caloric value of alternative foods should be determined. No 

information was presented on the specific egg or larval life stage was being consumed by 

shorebirds. Foraging behavior of knots, in particular, at sites other than Delaware Bay 

could provide insights into the importance of the Bay’s horseshoe crabs to shorebirds. The 

habitat section of the report should have included more information, if available, on the 

correlation between beach use by shorebirds and the distribution of horseshoe crab 

spawning females and eggs.

3.5. Availability of Horseshoe Crab Eggs

Although a sampling plan has been devised, no Bay-wide, systematic survey of egg availability 

has yet been conducted. Geographically limited surveys conducted in May, variably over the last 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 5 

four years, do not provide conclusive evidence of a trend in the abundance of surface eggs 

available to shorebirds. Likewise, there are not ample data to assess whether or not surface 

horseshoe crab eggs occur in abundances that will support Delaware Bay populations of migrant 

shorebirds. Although counts of spawning crabs have not changed between 1999 and 2002, trawl 

survey indices of all age-classes of crabs are now lower than they were in the early 1990s. 

Further analysis of egg data collected on New Jersey beaches and additional information on the 

temporal and spatial distribution of surface and sub-surface eggs is needed to thoroughly 

evaluate if there has been a significant trend in horseshoe crab egg abundance. Further 

refinement of the total shorebird energy budget is needed to determine how many eggs are 

required across the entire spring season. 

The Peer Review Panel believes that knowledge about the spatial and temporal patterns of 

horseshoe crab egg densities is critical to understanding how crab management affects 

migrant shorebird populations. Specifically, a clearer understanding of how eggs become 

available to shorebirds is needed. Energetic considerations indicate that horseshoe crab 

eggs are only profitable to shorebirds if they occur in high surface densities. The 

excavation and transport of eggs to the beach surface might only occur when spawning 

females occur in very high densities, and there may be a threshold female crab density at 

which sufficient numbers of eggs become available on the surface. Little appears to be 

known about the depletion of surface eggs attributable to shorebird, and other bird, 

predation. Depletion of surface eggs would be consistent with the hypothesis that crab eggs 

are a limiting resource for shorebirds. The Panel agrees that information from trawl 

surveys, given gear limitations for adequately sampling large numbers of crabs, indicates 

that horseshoe crabs in Delaware Bay are currently at lower levels than they were in the 

early 1990s. Uncertainty in recent estimates of sizes of horseshoe crab age classes 

precludes reasonable comparison of recruitment rates and harvest levels. The report 

would have benefitted from thorough analyses of datasets already collected on changes in 

egg densities on New Jersey beaches. An unified bioenergetics model for Delaware Bay 

shorebirds will be needed to integrate the information about available food with the 

requirements of shorebirds.

3.6. Shorebird Weight Gain in Delaware Bay

There is agreement that a smaller percentage of rufa red knots are making threshold departure 

weights by the end of May in recent years. These results are not dependent on inclusion of 1997, 

a year when shorebird-banding did not begin until 22 May. The different analytical approaches 

used to determine weight gains of Delaware Bay red knots (average weights of time-dependent 

catches, cohort analysis, and individual recaptures) have generated two hypotheses regarding 

decreases in rates of weight gain between 1997 and 2002 — either a greater proportion of red 

knots are arriving later in Delaware Bay in recent years, or red knots are increasingly unable to 

find sufficient food. In the first analytical approach, rates of weight gain in knots decreased 

through time, but in the latter two approaches they did not. Evidence suggests that rates of 

weight gain by semipalmated sandpipers have decreased in recent years, while rates of weight 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 6 

gain in least sandpipers, a more marsh-foraging species, remained stable. Patterns of decreasing 

(average) rates of weight gain were less consistent for ruddy turnstones and were not apparent in 

sanderlings. Ruddy turnstones can excavate eggs to feed on, and sanderlings are thought to 

commute regularly between Atlantic Ocean and Delaware Bay feeding sites. No hypotheses, as 

an alternative to decreased horseshoe crab egg availability, have been formulated to explain 

changes found in weight gains of semipalmated sandpipers. Semipalmated sandpipers do not 

winter in the same regions of South America as red knots. More information on the condition of 

South American stopovers and observations of individually marked birds are needed to fully 

discriminate between these two alternatives. Late arrival of knots could be caused by changes in 

spring weather patterns or by their inability to build fat stores at South American stopovers. Red 

knots can physiologically compensate for late arrival by increasing their rates of fat deposition 

while in Delaware Bay. 

The Peer Review Panel believes that the two hypotheses forwarded to explain changes in 

weight gain in Delaware Bay red knots are not mutually exclusive, but instead represent 

two factors which operate in tandem to affect departure weights from Delaware Bay. Both 

factors operate within the same year, although their relative importance may vary among 

years. The existing data, however, are not adequate to evaluate their relative importance 

for any year of record. But in any case, Delaware Bay must provide the food resources 

shorebirds need to adequately gain fat mass to make the flight to the arctic. That a lesser 

proportion of red knots are making minimal departure weights suggests that food 

resources in Delaware Bay may not be adequate. Similar feeding rates observed among 

species of different size supports the finding that the larger red knots should be most 

sensitive to decreases in food availability. The shorebird banding program in Delaware 

Bay would greatly benefit by a more cooperative approach to design and analysis. 

Procedures used in both analyses of weight gain were not documented adequately enough 

in supporting reports to allow independent evaluation. Patterns of weight gain were more 

clearly presented for semipalmated and least sandpipers. Unfortunately, attempts to 

estimate growth rate based on independent samples of body mass are inherently flawed, as 

assumptions must be made to accommodate the uncertainty in arrival times of birds. 

These assumptions lead to the possibility of conflicting results and additional controversy. 

Adjusting field methods to emphasize the collection of multiple measurements on 

individual birds would increase the sample of individually-marked birds and would 

ultimately strengthen conclusions about annual changes in rates of weight gain. 

3.7. Shorebird Survival

Shorebird return rates (on southward migration) relative to stopover departure weights indicate 

that the inability to gain sufficient weight at stopover sites can reduce survivorship for red knots 

(Calidris canutus) and semipalmated sandpipers (Calidris pusilla), which supports the link 

between stopover conditions and population trends. Recent estimates of adult survival and 

productivity of rufa red knots are substantially lower than estimates for knot populations 

wintering in Europe and Australia; these knot populations also breed in arctic regions and 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 7 

undertake long-distance, long-hop migrations. Sustained low levels of vital rates could cause a 

drastic decline in the knot population. Evidence generated through population modeling, 

however, was insufficient to evaluate the probabilities of extinction under the current range of 

demographic values. 

The Peer Review Panel supports the conclusion that low-weight red knots had a lower 

return rate, but found the estimates of adult survival to be highly variable among periods. 

Further details of the analytical procedures used for estimating survival rates are needed to 

thoroughly evaluate these results for application to management decisions. To fully 

evaluate the biological significance of survival rates and juvenile ratios, better information 

on non-breeding distribution and movements of juveniles is needed. Because estimates 

among years were from different sites, the variability of these estimates among sites should 

be evaluated. Overall, the Panel believes that design and analysis of future mark-resight/ 

recapture studies could be improved to remove ambiguities in interpretation of results and 

to take better 

advantage of the large number of banded birds. Use of field-readable, individuallynumbered color flags should be thoroughly evaluated.

4.0. RECOMMENDATIONS

Horseshoe crab management actions already taken (for example, bait bags, harvest reductions, 

alternative bait development, designation of the Carl N. Shuster, Jr. Horseshoe Crab Reserve) 

have likely improved conservation of crabs and shorebirds. Despite these actions, and the 

stability of spawning horseshoe crab numbers over the last four years, the population of red 

knots, and perhaps other species, has declined. As a general management action, the U. S. 

Shorebird Conservation Plan suggests that any declining shorebird population should be 

stabilized and then restored to population levels of the late 1970s and early 1980s. Accordingly, 

shorebirds in Delaware Bay should be managed to maintain current population sizes, and 

decreasing populations should be stabilized and then increased. 

Based on the shorebird and crab information currently available, the Shorebird Technical 

Committee therefore recommends that the Horseshoe Crab Management Board pursue a 

management strategy that is more risk-averse to shorebirds. Using an adaptive approach, 

continued or improved monitoring programs for shorebirds, horseshoe crabs, and horseshoe crab 

eggs are needed to evaluate results of management actions and to provide guidance for future 

selection of management alternatives. The Shorebird Technical Committee supports the 

cooperative effort of the Horseshoe Crab Technical Committee and the Horseshoe Crab Stock 

Assessment Committee to develop and implement various crab surveys. Specific 

recommendations of the Shorebird Technical Committee follow, which were generally supported 

by all Committee members. Peer Review Panel comments are also included, as bolded text, 

below. 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 8 

4.1. Direct Management

 4.1.1. Horseshoe crab egg abundance

Until further information is available on whether or not current egg abundances are sufficient for 

shorebirds to reach threshold departure weights, the Committee recommends further reductions 

in bait landings for New Jersey, Delaware, and Maryland. Although the Committee realizes 

there currently are no biological reference points on which to base reduction amounts, total 

reductions in the range of 50 to 75% below the Reference Period Landings might be considered. 

Committee members could not reach consensus on the amount of reduction, if any, that would be 

considered risk-averse. Because crabs caught in Federal waters from New York and to Virginia 

ca be landed in any of the mid-Atlantic states, in New York and Virginia might also be 

considered. Mandatory use of bait bags and development of alternative baits could contribute to 

reduced bait use of horseshoe crabs. 

The Peer Review Panel supports a reduction in harvest but suggests that this action be 

viewed as an interim solution until integrated and comprehensive models are constructed 

to set reasonable biological objectives for shorebirds. Although the Panel is unsure about 

the amount of the reduction that is immediately needed, the numerous indications of 

shorebird population declines suggests that harvest rates should be at or below the current 

levels. Based on very limited data, a 75% reduction would ensure recruitment of female 

crabs into the breeding population at the low bound of the population estimate of 

primiparus female crab; a 66% reduction would allow no population growth at this level. 

Development of conservation methods to use bait crabs most efficiently is worthwhile. 

Landings in states other than New Jersey, Delaware, and Maryland should be carefully 

tracked.

 4.1.2. Seasonal beach closures

To increase abundance and availability of horseshoe crab eggs for feeding shorebirds, restrict 

hand harvest of horseshoe crabs, vehicles, humans, and dogs on State- and Federally-owned 

beaches important to shorebirds from 1 May to 7 June, the period of highest shorebird use, along 

the Delaware Bay shoreline of Delaware and New Jersey. Evaluate the effectiveness of 

restrictions. 

The Peer Review Panel believes that this is a reasonable short-term action to increase the 

number of horseshoe crab eggs available to migrant shorebirds. Evaluation of these 

restrictive measures should be undertaken.

 4.1.3. Habitat protection and enhancement

Encourage Delaware and New Jersey to continue environmentally responsible beach 

nourishment and other enhancement projects that increase high quality habitat for spawning 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 9 

crabs and feeding shorebirds. Consider long-term protection measures, including easements and 

acquisition, for beaches that are important for crab spawning and shorebird foraging. Evaluate 

the effectiveness of beach enhancement activities. 

The Peer Review Panel believes further evaluation of the effects of beach nourishment on 

horseshoe crab spawning and invertebrate infauna are warranted before broad-scale 

activities are undertaken. If results of these evaluations, preferably using a before-andafter experimental design, are favorable, specific prescriptions of “environmentally 

responsible” practices should be developed. Evaluations and prescriptions should be 

sensitive to the geographic scale of application. Long-term protection of beaches would 

likely be a beneficial conservation measure.

4.2. Needed Analyses

 4.2.1. Horseshoe crab egg abundance

Complete analyses of horseshoe crab egg abundance data that have already been collected on 

New Jersey beaches to further evaluate evidence of a change in egg abundance. 

 4.2.2. Shorebird breeding-ground conditions

Compile information on annual weather conditions and predation pressure on breeding grounds 

to assess short- and long-term effects on red knot survival and reproduction and on semipalmated 

sandpiper population change. Report information on density, hatching success, and habitat use 

on breeding grounds. 

 4.2.3. Shorebird diet and energetics

Complete stable isotope analysis for remaining Delaware Bay shorebird species to quantify their 

dependence on horseshoe crab eggs. Develop the best possible estimate of the total energy 

needed and horseshoe crab eggs required by all migrant Delaware Bay shorebirds. Complete 

analysis of information on alternative foods available to Delaware Bay shorebirds to determine if 

other energy sources exist that could supplement horseshoe crab eggs. Report on role of 

nocturnal foraging. 

The Peer Review Panel encourages efforts to expedite the reporting and analysis of all 

previously-collected data pertinent to topics addressed in the report. The Panel also 

encourages the involvement of biometricians in these analyses.
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 10 

4.3. Improved Monitoring and Research

4.3.1. Bay-wide horseshoe crab egg abundance

Support implementation of the Bay-wide egg survey to determine abundance of, and ultimately 

trend in, horseshoe crab eggs on Delaware Bay beaches. Information is needed on egg 

deposition and movements to understand what makes eggs available to shorebirds on Delaware 

Bay beaches. 

 4.3.2. Shorebird population surveys

Continue, and expand, the aerial survey of South American wintering grounds of red knots to 

identify additional concentration areas and track population changes. Include areas with winter 

aggregations of semipalmated sandpipers. Develop and evaluate other counting and 

demographic methods to track populations of shorebirds. 

 4.3.3. Individually-marked shorebirds

Increase marking and scan-sampling of red knots on wintering grounds and in Delaware Bay to 

track changes in population size, annual survival, and reproductive success. Expand efforts to 

include semipalmated sandpipers. Use individually color-flagged and radio-tagged shorebirds to 

determine movements into and within Delaware Bay to evaluate the late-arrival hypothesis. 

 4.3.4. Measurements of weight gain

Continue to monitor shorebird weights in Delaware Bay, while minimizing disturbance to 

foraging shorebirds. Agree on standard data collection techniques, for both sides of Delaware 

Bay, and record wing length and time after capture that weighing takes place. Develop a 

common, Bay-wide database and agree on analytical approaches. 

 4.3.5. Southern stop over quality

Assess habitat quality of stopovers south of Delaware Bay to determine if South American sites 

are providing enough food resources for migrant red knots and other shorebird species to gain 

the weight needed to undertake trans-ocean flights. 

The Peer Review Panel believes that virtually all management, research, and monitoring 

programs would benefit from being placed within a more holistic and comprehensive 

framework in which models are used to provide coherent structure for both combining 

existing information and predicting consequences of management activities. Currently, 

many of the research and monitoring efforts are fragmented and isolated, and it is unclear 

whether appropriate information is presently collected to best aid management decisions. 

The Panel encourages the Shorebird Technical Committee to work with all partners and 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 11 

stakeholders to develop a more comprehensive and integrated research and monitoring 

program. Theoretical models should be developed for core components of this program 

that would include: 1) integrated shorebird energetics and horseshoe crab egg availability, 

2) shorebird demographics, and 3) monitoring design and analysis. Even in the absence of 

detailed quantitative information, explicit, well-developed models can illustrate the most 

likely explanatory hypotheses, identify speculative and real data linkages, highlight key 

gaps in current knowledge, and clarify specific goals and objectives. For many of the 

research and monitoring components, more emphasis should be placed on the use of 

information collected on individually-marked shorebirds, including radio-tagged birds. A 

premium should be placed on the development of robust survey and experimental designs.

5.0. SHOREBIRD TECHNICAL COMMITTEE MEMBERSHIP

Karen Bennett Shorebird biologist, Delaware Division of Fish and Wildlife 

Gregory Breese Shorebird biologist, U. S. Fish and Wildlife Service 

Joanna Burger Shorebird biologist, Rutgers University 

David Carter Coastal zone manager, Delaware Coastal Management Program 

Robert Gorrell Fisheries biologist, National Marine Fisheries Service 

Brian Harrington Shorebird biologist, Manomet Center for Conservation Sciences 

Marshall Howe Shorebird biologist, U. S. Geological Survey 

Stewart Michels Fisheries biologist, Horseshoe Crab Technical Committee 

Mike Millard Fisheries biologist, U. S. Fish and Wildlife Service 

David Mizrahi Shorebird biologist, New Jersey Audubon Society 

Lawrence Niles Shorebird biologist, New Jersey Division of Fish and Wildlife 

Nellie Tsipoura Shorebird biologist, National Resource Defense Council (formerly) 

Brad Andres Coordinator, Shorebird biologist, U. S. Fish and Wildlife Service 

6.0. PEER REVIEW PANEL PARTICIPANTS

Dr. H. Jane Brockmann University of Florida, Department of Zoology 

Dr. Chris S. Elphick University of Connecticut, Department of Ecology and 

Evolutionary Biology 

Dr. James D. Fraser Virginia Polytechnic Institute & State University, Department of 

Fisheries and Wildlife Sciences 

Dr. Patrick G. R. Jodice South Carolina Cooperative Fish and Wildlife Research Unit, 

Clemson University 

Dr. Erica Nol Trent University, Biology Department 

Dr. Adrian H. Farmer U. S. Geological Survey, Fort Collins Science Center 

Dr. James D. Nichols U. S. Geological Survey, Patuxent Wildlife Research Center 

Dr. John R. Sauer U. S. Geological Survey, Patuxent Wildlife Research Center
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 12 

B. Shorebird-Horseshoe Crab Assessment

1.0. INTRODUCTION

1.1. Shorebird Technical Committee

The Atlantic States Marine Fisheries Commission asked the U. S. Fish and Wildlife Service to 

form a Shorebird Technical Committee that would provide technical guidance, regarding effects 

that horseshoe crab management actions could have on shorebird populations, to the Horseshoe 

Crab Management Board. Members and Terms of Reference of this committee are provided 

along with this report. The immediate task of the committee is to produce a peer-reviewed report 

that reviews and synthesizes unpublished and published information on shorebird populations, 

shorebird habitat use, shorebird energetic requirements, threats to shorebird populations, and 

horseshoe crab egg abundance. From this report, the committee will generate a set of 

conclusions, management recommendations, and research needs. The report and 

recommendations will also undergo an independent peer review. 

1.2. Horseshoe Crabs, Shorebirds, and Delaware Bay

Reported commercial landings of horseshoe crabs (Limulus polyphemus) on the Atlantic coast of 

the U. S. increased dramatically, relative to the previous 4 decades, in the mid 1990s (Figure 4 in

Walls et al. 2002). Horseshoe crabs are most abundant between Virginia and New Jersey 

(Shuster 1982), and Delaware Bay supports the largest concentration of spawning individuals 

(Shuster and Botton 1985, Botton and Ropes 1987). Delaware Bay also supports large 

aggregations of shorebirds (>500,000 individuals) during spring migration and is one of the most 

numerically important spring stopover sites in North America (Clark et al. 1993). Timing of 

shorebird arrival coincides with the availability of an abundant food source — the eggs released 

by spawning horseshoe crabs — that is used to build fat reserves for non-stop flights to breeding 

grounds in the Canadian arctic (Myers 1986). Hence, concern has been raised about the negative 

effect that crab harvest might have on shorebirds during spring migration (see Berkson and 

Shuster 1999). Although several actions have recently been taken to conserve horseshoe crab 

populations (restrictions on harvest, delineation of a no-fishing reserve, use of bait bags, and 

development of alternative baits), the current status of horseshoe crabs, shorebirds, and their 

relationship remains unclear (see Walls et al. 2002). 

1.3. Economic Value of Crabs and Shorebirds

Horseshoe crabs are commercially harvested for use in the biomedical industry (where crabs are 

bled and usually returned to the ocean) and as bait in the American eel (Anguilla rostrada) and 

“conch” (really a whelk, Busycon spp.) pot fisheries (Atlantic States Marine Fisheries 

Commission 1998a*). Eels are then used for either finfish bait or human consumption. An 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 13 

economic analysis indicates that the annual social welfare benefit (the benefit to consumers 

because they are able to purchase goods and services below their willingness to pay) of the 

fishery along the entire Atlantic coast is about $150 million for the biomedical industry and $21 

million for the commercial eel and whelk fisheries (Manion et al. 2000*; 1999 dollars). 

Regional economic outputs (New Jersey, Delaware, Maryland) are valued (1999 dollars) at $2.2 

– 2.8 million for the eel/whelk fisheries, $26.7 – 34.9 million biomedical industry, and $6.8 – 

$10.3 million for recreational birding (Manion et al. 2000*). Another study estimated that 6,000 

– 10,000 recreational birders visited New Jersey’s Delaware Bay beaches in the spring and 

contributed a gross economic value (total gross output + consumers’ surplus) of 11.8 – 15.9 

million to local communities (Eubanks et al. 2000*). Overall, the biomedical use of horseshoe 

crabs is the most economically valuable across the entire Atlantic coast, and the regional value of 

crabs to recreational birding is at least, if not greater, than the commercial value. 

1.4. Evaluation Approach

Under the precautionary principle (Buhl-Mortensen and Welin 1998), Smith et al. (2002c) 

suggest that it would be risk prone to assume species’ risk is low unless a statistical power 

analysis had shown that a study design was powerful enough to detect biologically meaningful 

change. Peterman and M’Gonigle (1992) outline 3 outcomes when statistical power is 

incorporated into decision-making: 1) a biologically meaningful and statistically significant 

decline results in harvest restrictions, 2) no evident decline and high power results in no harvest 

restrictions, and 3) a biologically meaningful, statistically non-significant decline and low power 

increases species’ risk. In the latter case, high uncertainty should trigger harvest restrictions as a 

risk-averse strategy. Power analyses generally address singular datasets. To judge an overall 

effect when multiple studies or datasets test a singular null hypothesis, a concordance of 

evidence approach is a reasonable way to evaluate overall effects (Andres 1999). Thus, a 

preponderance of evidence in one direction or the other should result in clear management action 

(including no action). Therefore, the committee will use the concordance, or preponderance, of 

evidence approach described above to evaluate the report’s contents. Because many regression 

analyses are sensitive to the time period selected, and results varied widely depending on starting 

year, analyses of some population data were compared among 2 groups — before 1997 and after, 

and including, 1997. More intensive shorebird and horseshoe crab studies were generally 

initiated during, or after, 1997. An “*” after the year of a citation indicates that the material is an 

unpublished report, a submitted manuscript, or an abstract. 

2.0. DELAWARE BAY SHOREBIRDS

2.1. Species Considered

Although several shorebird species will be considered in this report, attention will primarily 

focus on the red knot (Calidris canutus). Available information is greatest for the red knot and is 

less extensive for the ruddy turnstone (Arenaria interpres), sanderling (Calidris alba), 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 14 

semipalmated sandpiper (Calidris pusilla), and least sandpiper (Calidris minutilla). Relatively 

little specific information exists on the dunlin (Calidris alpina), short-billed dowitcher 

(Limnodromus griseus), or long-billed dowitcher (Limnodromus scolopaceus). Information 

presented is specific to taxa that use Delaware Bay. Aside from the least sandpiper, species were 

selected because of their reliance on beach habitats and their frequency of observation on 

Delaware Bay aerial surveys from 1986 to 2002 (see Clark et al. 1993; Table 5.4): semipalmated 

sandpiper (40%), ruddy turnstone (29%), red knot (17%), sanderling (6%), dunlin (6%), and 

long-/short-billed dowitcher (2%). The least sandpiper was chosen because of its contrasting us 

of marsh habitats, rather than beaches, which indicates less of a dietary reliance on horseshoe 

crab eggs. Long-billed dowitchers are only rarely observed on Delaware Bay beaches. 

2.2. Conservation Status and Protection

The U. S. Shorebird Conservation Plan describes 6 factors of vulnerability (population trend, 

relative abundance, breeding threats, non-breeding threats, breeding distribution, and nonbreeding distribution) that were used to determine the conservation concern of North Americanbreeding shorebird populations (Brown et al. 2001*). Combinations of these factors were used 

to designate the conservation concern of shorebird populations as: highly imperiled, high 

concern, moderate concern, low concern, or not at risk. This type of assessment was used by the 

U. S. Fish and Wildlife Service (2002*) to develop a Congressionally-mandated list of Birds of 

Conservation Concern. Of the 8 species mentioned in Section 2.1, the red knot, ruddy turnstone, 

and sanderling are listed as species of high conservation concern in the U. S. Shorebird 

Conservation Plan (Brown et al. 2001*), and the red knot and short-billed dowitcher (primarily 

due to central and western populations) are listed as Birds of Conservation Concern by the U. S. 

Fish and Wildlife Service (2002*). 

All migrant species are protected in the U. S. under the statutes of the Migratory Bird Treaty Act, 

as amended, and are recognized in international agreements such as the Western Hemisphere 

Convention and the Convention on Arctic Flora and Fauna. Because of its value to birds, 

Delaware Bay has received international recognition as a Western Hemisphere Shorebird 

Reserve Network site of hemispheric importance (>500,000 shorebirds annually), a Wetland of 

International Importance under the Ramsar Convention (>1% of a flyway waterbird population), 

and an Important Bird Area of global significance (because of large aggregations). 

2.3. Vulnerability of Long-distance Migrant Shorebirds and the Red Knot Focus

Piersma and Baker (2000) outlined several critical life history traits of migrant shorebirds that 

include: low productivity, long lifespan, trophic specialization, gregariousness, 

immunospecialization, sometimes strong sexual selection, long flights, metabolic adaptations for 

flight endurance, a precise annual cycle clock, orientation mechanisms, geographic bottlenecks 

(reliance on a small number of wintering and stopover sites), and reduced genetic variability. 

The red knot epitomizes these critical life history traits, and their trophic specialization on 

marine environments makes them vulnerable to perturbations to these habitats, particularly at 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 15 

geographic bottlenecks. Piersma and Baker (2000) suggested that populations of long-distance, 

long-hop migrant shorebirds, such as the red knot, are mainly constrained by access to high 

quality non-breeding habitats, a concept previously championed by Myers (1983). 

Hitchcock and Gratto-Trevor (1997) modeled a local decline of semipalmated sandpipers and 

found that out of 5 variables (fecundity, adult survivorship, juvenile survivorship, delayed 

recruitment, and immigration), adult survivorship had the most significant influence on the 

population decline. Reductions in adult survival, through over-hunting and possibly stopover 

habitat change, are suggested to have caused the drastic decreases, and possible extinction, of 

Eskimo and slender-billed curlews (Gill et al. 1998, Gretton 1991). Piersma and Baker (2000) 

suggest that the probability of death by exhaustion or infection increases exponentially and 

reproduction decreases logarithmically as energy stores at stopover departure time and body 

mass on breeding ground arrival decrease. Because changes in population size are so sensitive to 

levels and variation in adult survival, conservation of high quality stopover and wintering sites is 

critical. Historical population bottlenecks may have caused the low genetic variability currently 

observed in some shorebird populations (Piersma and Baker 2000). 

2.4. Red Knot Distribution

The red knot breeds in arctic regions of Siberia, Alaska, Canada, and Greenland and is the largest 

arctic-nesting sandpiper (i.e. in the genus Calidris) in North America. Three populations of red 

knots are found in North America: the subspecies C. c. islandica breeds in the northeastern high 

Canadian arctic and Greenland, migrates through Iceland, and winters in western Europe; C. c. 

roselaari likely breeds in Alaska and migrates along the Pacific coast and likely through interior 

North America; and C. c. rufa breeds in the central Canadian arctic and migrates primarily along 

the eastern coast of North America (Piersma and Davidson 1992). Most rufa individuals winter 

along the coasts of South America, and the largest number of individuals are found along the 

Chilean and Argentine shorelines of Tierra del Fuego (Morrison and Ross 1989a). Breeding 

origins of knots wintering in the southern U. S. and migrating through the interior of the 

continent are not completely known (Harrington 2001). 

2.5. Red Knot Annual Cycle

Southward migration of adult red knots begins in mid-July when between 5,000–15,000 birds 

have been observed in James Bay, Canada (Morrison and Harrington 1992). Adult knots arrive 

on the Atlantic coast of North America from mid-July to early August. Juveniles depart later 

than adults and migrate through eastern North America from late August to mid-September. 

Concentrations of fall migrants are more disperse than during spring migration (see section 3.3). 

September aggregations of 1,800–12,000 knots have recently been reported along the coast of 

Georgia (Harrington and Winn 2001*). Knots banded in Georgia generally winter in Florida 

(likely C. c. roselarii), where the mean wintering population is about 6,300 " 3, 400 (SD) 

individuals (Harrington et al. 1988). Individuals wintering in southwest Florida have high site 

fidelity (Below 2001*). Rufa knots depart the northeastern U. S. by late August and early 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 16 

September to undertake a trans-Atlantic Ocean flight to arrive on the north coast of the 

Suriname, French Guiana, and Brazil. From there, they overfly central Brazil, stop briefly in the 

Pantanal (on the Rio Negro’s salt lakes late September to early October), reach maximum 

abundance in Lagoa do Peixe in October, and arrive in Tierra del Fuego by early November. 

Northward migration in Argentina begins in mid-February and persists through early April. 

From mid-February to mid-March, 5,000–7,000 knots were present daily in Bahía de San 

Antonio Oeste, Argentina (González et al. 2001). Main passage through Lagoa do Peixe, Brazil, 

(used by about 7,000 knots) occurs from mid-April through the first week of May (Nascimento 

2001*). Birds depart the Maranhão coast of northeastern Brazil, where >10,000 knots have been 

observed (Nascimento 2001*), during early to mid-May. April aggregations of $6,000 knots 

have been noted in South Carolina (Harrington and Winn 2001*) and peak counts of 7,710–

8,955 knots have been recorded on the outer coast of Virginia (Truitt et al. 2001*), where birds 

banded in Argentina (27 knots), Delaware Bay (27) and Brazil (4) were observed. Large 

numbers of birds (maximum counts range from 19,445 to 95,490 knots) arrive in Delaware Bay 

during the second week of May and usually depart by the end of May or early June. Passage 

flights of knots have been observed in James Bay, Canada, (but not landing) in late May and 

early June (Morrison and Harrington 1992). Knots arrive on their Southampton Island breeding 

grounds during the first 10 days of June (P. Smith, Canadian Wildlife Service, personal 

communication). Incubation is 21–22 days, and both parents incubate the 4-egg clutch (see 

Harrington 2001). Fledging period is estimated to be about 18 days (see Harrington 2001). 

Females may depart the breeding grounds before males (see Harrington 2001). 

2.6. Distribution and Migration Routes of Other Species

 2.6.1. Ruddy turnstone

A Holarctic species, 3 populations of ruddy turnstones breed in North America: A. i. intepres

breeds in western and northern Alaska and winters on Pacific islands and the Pacific coast of 

North America, a disjunct population A. i. intepres breeds in the Canadian high arctic and 

winters in Europe, and A. i. morinella breeds in the central and low Canadian arctic, into 

northeastern Alaska, and migrates primarily along the eastern coast of North America, including 

through Delaware Bay (Nettleship 2000). Highly coastal in its habitats, morinella winters in the 

southern U. S., throughout the Caribbean, and along the northern and eastern coasts of South 

America south (a few) to Tierra del Fuego (Morrison and Ross 1989a). Turnstones wintering on 

the western coasts of Central and South America may be either morinella or interpres (Nettleship 

2000). The greatest winter aggregations of morinella occur in northern South America 

(Morrison and Ross 1989a). 

2.6.2. Sanderling

Breeding distribution of the sanderling is similar to that of the red knot, but no subspecies have 

been described (MacWhirter et al. 2002). The wintering distribution is much broader than the 

knot —sanderlings are found along the shorelines of every continent except Antarctica 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 17 

(MacWhirter et al. 2002). Sanderlings nesting in the northeastern Canadian High arctic are 

thought to winter in Europe, and other birds breeding in the eastern arctic likely use eastern 

Atlantic and interior flyways (MacWhirter et al. 2002). The population passing through 

Delaware Bay probably winters in the southeastern U. S., Caribbean, and South America 

(Morrison et al. 2001). The greatest aggregations of wintering birds are found along the Pacific 

coast, rather than the Atlantic coast, of South America (Morrison and Ross 1989a). 

2.6.3. Semipalmated sandpiper

The semipalmated sandpiper breeds throughout the well-vegetated tundra of arctic and sub-arctic 

regions of North America. Although populations have not differentiated to the point of 

subspecies recognition, a decreasing cline in body size occurs from east to west (Gratto-Trevor 

1992). Semipalmated sandpipers that use Delaware Bay are thought to nest in the eastern 

Canadian arctic and use the Atlantic flyway to travel to wintering grounds along the Caribbean 

and Atlantic coasts of South America (Harrington and Morrison 1979). Winter aggregations are 

greatest along the northern coast of South America (Morrison and Ross 1989a). 

2.6.4. Dunlin

The breeding distribution of the dunlin is one of the most cosmopolitan of all small sandpipers. 

Populations in North America have differentiated into 3 subspecies: C. a. arcticola breeds in 

northern Alaska and northwest Canada and winters in southeastern Asia, C. a. pacifica breeds in 

western Alaska and winters primarily along the west coast of North America, and C. a. hudsonia, 

which passes though Delaware Bay, breeds in the eastern and central Canadian arctic and winters 

on the Atlantic and Gulf of Mexico coasts (Warnock and Gill 1996). Few dunlins of any 

subspecies winter south of Mexico (Warnock and Gill 1996). More dunlins may be found in 

marshes than on beaches of Delaware Bay (Burger et al. 1997). 

2.6.5. Short-billed dowitcher

The short-billed dowitcher is restricted to North America, where 3 recognizable subspecies 

occur: L. g. griseus breeds in eastern Canada and winters in Central and South America, L. g. 

hendersoni breeds in Central Canada west of Hudson Bay and winters in on the Atlantic and 

Gulf of Mexico coasts, and L. g. caurinus breeds in southern Alaska and winters along the 

Pacific coast from California to South America (Jehl et al. 2001). Short-billed dowitchers in 

Delaware Bay are likely L. g. griseus. More short-billed dowitchers might use Delaware Bay 

marshes than beaches (Burger et al. 1997). 

2.6.6. Long-billed dowitcher 

The long-billed dowitcher is monotypic throughout its range in northeastern Russia, Alaska, and 

northwestern Canada (Takekawa and Warnock 2000). Its breeding range is more northern than 

the congeneric short-billed and Asiatic dowitchers (L. semipalmatus). Long-billed dowitchers 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 18 

winter on the Pacific coast from southern British Columbia to El Salvador and eastward to North 

Carolina (Takekawa and Warnock 2000). Most spring dowitchers in Delaware Bay are shortbilleds. 

2.6.7. Least sandpiper

The least sandpiper has the broadest and most southern distribution of any Calidris sandpiper 

breeding in North America; their range stretches across the northern boreal and sub-arctic region 

from Newfoundland to western Alaska (Cooper 1994). Populations have not differentiated to the 

point of subspecies recognition, but birds using the Atlantic flyway, including Delaware Bay, 

likely breed in eastern Canada (Morrison et al. 2001) and winter in the southeastern U. S., 

Caribbean, and northern South America. Winter aggregations are greatest along the northern 

coast of South America (Morrison and Ross 1989a). Least sandpipers tend to use marshes, 

rather than shorelines, of Delaware Bay during spring migration and are not recorded in large 

numbers on aerial beach surveys (see Clark et al. 1993). 

3.0. ABUNDANCE AND DISTRIBUTION OF HORSESHOE CRABS

The horseshoe crab ranges from the Yucatan Peninsula to Maine and is most abundant between 

Virginia and New Jersey (Shuster 1982). The Delaware Bay hosts the largest concentration of 

spawning horseshoe crabs worldwide (Shuster and Botton 1985). Within Delaware Bay, 

spawning horseshoe crabs have been reported from Woodland Beach to Cape Henelopen in 

Delaware and from Sea Breeze to Cape May in New Jersey (Smith et al. 2002b,c). Some 

spawning may occur farther up the estuary but is probably restricted by salinity and the 

increasing presence of salt marsh and peat banks (Shuster and Botton 1985). Botton et al. (1988) 

observed fewer spawning crabs in proximity of peat beds. Density of spawning crabs on beaches 

varies annually (Smith et al. 2002b), although beaches within the lower to middle portion of 

Delaware Bay tend to support the highest spawning concentrations. 

The high concentration of breeding crabs may be attributable to the abundance of sheltered, 

coarse-grained, well-drained sandy beaches that are conducive to spawning and egg incubation. 

In addition, large intertidal flats adjoining, or in close proximity, to these beaches likely provide 

important nursery habitat. High, wide, low-tide terraces also dissipate wave energy and create 

narrow, steep beaches. Low wave energy associated with tidal creeks may explain why high 

concentrations of horseshoe crab spawning have been observed in sandy areas within tidal 

creeks. Botton et al. (1988) estimated that only 10% of the New Jersey shoreline in Delaware 

Bay provided optimal horseshoe crab spawning habitat. However, horseshoe crabs are 

opportunistic and use other habitats that are less conducive to egg survival. Shuster (1982) 

suggested that beach temperature, moisture level, and oxygen concentration affected horseshoe 

crab egg viability. Eggs remain in the sand for 2–4 weeks before hatch. Crabs have been known 

to spawn subtidally, but the extent to which this occurs is unknown (Atlantic States Marine 

Fisheries Commission 1998a*). Female crabs burrow into sediments to lay their eggs. Kraeuter 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 19 

and Fegley (1994) found that mean depth of sediment mixing (11 cm) corresponded closely to 

the mean carapace height of female crabs. 

Mature horseshoe crabs move inshore from deeper portions of the bay and coastal waters in late 

spring to spawn (Atlantic States Marine Fisheries Commission 1998a*). Spawning in Delaware 

Bay may occur as early as April and last into July (Shuster and Botton 1985), with peak 

spawning activity typically occurring around the new and full moons in May or June. Spawning 

is usually higher on the highest of the 2 daily tides, which typically occur at night in Delaware 

Bay. Male horseshoe crabs often precede females to a beach and await the arrival of females 

(Shuster 1996). Maximum concentrations of spawning crabs may differ temporally between the 

New Jersey and Delaware sides of the Bay. For example, in 1999 maximum horseshoe crab 

spawning occurred in mid-May in New Jersey, but peaked in early June in Delaware (Smith et al. 

2002c). Spawner abundance (adult females) during 1999–2000 was higher in Delaware than in 

New Jersey, but was higher in New Jersey in 2002 (Smith and Bennett 2003*). Previously, 

authors have reported higher spawning concentrations in New Jersey (Shuster and Botton 1985). 

Smith et al. (2002c) found that lunar phase (new/full) and wave height had the most significant 

effects on spawning activity, but effective modeling of spawning activity included a combination 

of time, place, weather, and tide height. In terms of an optimal design to survey spawning crabs, 

an increase in the number of sampled beaches had the greatest effect on reducing the CV 

(coefficient of variation) of the estimate of spawning females. Thus, spawning varied spatially 

and temporally and was moderated by wave height 

Two years of Peterson disc tagging in Delaware Bay showed that horseshoe crabs spawn 

multiple times over a season, with males spawning more frequently than females, and that crabs 

appear to exhibit limited beach fidelity from year to year (Eyler and Millard 2002*). A 

combined acoustic and radio-tag study conducted by Brousseau et al. (2002*) also showed strong 

within-season fidelity to spawning beaches; 91% of the 23 crabs successfully tracked returned to 

spawn on beaches where they were initially tagged in the same year. Although sample sizes 

were low and observation duration was relatively short, the study also found that tagged female 

crabs remained between 50 and 250 m offshore from their known spawning beaches. 

Besides providing food to shorebirds, horseshoe crab eggs and larvae are seasonal foods for fish 

[particularly striped bass (Morone saxatilis) and white perch (Morone americana)], crabs, and 

gastropods (Shuster 1982). Contributions of horseshoe crab eggs and larvae to the diet of these 

species is generally unknown (Atlantic States Marine Fisheries Commission 1998a*). Buckel 

and McKown (2002) found horseshoe crab eggs and juveniles in 42% of stomachs, which 

comprised 44% of identifiable prey items, of age 1 striped bass collected in beach seines in Long 

Island and Staten Island. Lutcavage and Musick (1985) determined that the most common prey 

of loggerhead turtles (Caretta caretta) in Chesapeake Bay were adult and sub-adult horseshoe 

crabs, which can represent $42% of the diet (Lutcavage 1981). Botton (1993) observed gulls 

feeding on live adult horseshoe crabs that were stranded on exposed beaches. Gulls attacked the 

exposed book-gills of overturned crabs. Through transect surveys, mortality was estimated at 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 20 

7,760 crabs/km, and gull predation was suggested to be the most important source of mortality to 

crabs when they were exposed on spawning beaches. 

4.0. POTENTIAL THREATS TO SHOREBIRDS

4.1. Heavy Metal Concentrations in Shorebirds and Horseshoe Crabs

Data from the 1990s indicated that the levels of metals in body feathers of 3 species of 

shorebirds from Delaware Bay were generally not high enough to directly affect birds 

themselves (Burger et al. 1993). However, mercury levels were relatively high (red knot = 1.1 

ppm, sanderling = 2.8 ppm) and suggested a need for further monitoring. Burger et al. (2002b) 

examined the levels of arsenic, cadmium, chromium, lead, manganese, mercury and selenium in 

the eggs, leg muscle, and carapace musculature (hereafter called apodeme, the fleshy part of the 

carapace) in female horseshoe crabs from 4 beaches in New Jersey and 4 beaches in Delaware to 

determine whether there were location differences in metal levels, and whether these levels were 

high enough to cause effects in birds that eat them. If the crabs were obtaining heavy metals in 

the period immediately before egg laying, and sequestering them in their eggs, then the eggs 

from female crabs that nest farther north in the bay, where industrialization is greater, should 

have higher levels. Eggs were examined because they could be compared to levels reported 

earlier from the same study area (Burger 1997), and they are the major food resource for 

shorebirds migrating through the bay. Overall, there were some differences in metal levels of the 

crabs collected in New Jersey and Delaware, but the differences were generally not great and 

there was no consistent pattern in the bay. Previous work demonstrated horseshoe crab egg 

sensitivity to heavy metal toxicity (Botton et al. 1998, Botton 2000, Itow et al. 1998a, 1998b). 

Manganese concentrations in Delaware crabs (but not the eggs) were >2x than those from New 

Jersey. There were some location differences for all 3 tissues (except eggs in Delaware) for both 

New Jersey and Delaware. Although the differences were significant, they were generally not 

great; there were no order of magnitude differences among collection sites. Contaminant levels 

were generally low. The levels of contaminants found in horseshoe crabs were well below those 

known to cause adverse effects in the crabs themselves or in organisms that consume them or 

their eggs. Contaminant levels have generally declined in the eggs of horseshoe crabs from 

1993–2000 in Delaware Bay, suggesting that contaminants are not likely to be a problem for 

secondary consumers. While it is important to examine the levels of metals in horseshoe crabs 

from Delaware Bay, it is equally important to understand contaminant patterns along the east 

coast of North America. This study is reported below. 

Burger et al. (2002a) examined the levels of metals (arsenic, cadmium, chromium, lead, 

manganese, mercury, and selenium) in the eggs, leg muscle, and apodeme of 100 horseshoe 

crabs collected at 9 sites from Maine to Florida. Crabs were collected from the spawning 

beaches during 2000. Only large females (n = 5–16 per location) were collected to control for 

possible sexual differences and to increase the likelihood of obtaining egg samples. Arsenic 

levels were the highest, followed by manganese and selenium, and levels for the other metals 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 21 

averaged below 100 ppb for most tissues. Arsenic and mercury levels were highest in the leg 

muscle, cadmium, lead, manganese, and selenium levels were highest in eggs, and chromium 

levels were highest in the apodeme. There were significant geographical differences for all 

metals in all 3 tissues. No one geographical site had the highest levels of >2metals. Arsenic, 

with the highest levels overall, was highest in Florida in all 3 tissues. Manganese levels were 

highest in Massachusetts for eggs and apodeme, but not leg, which was highest in Port Jefferson, 

New York. Selenium was highest in apodeme from Florida, and in eggs and leg muscle from 

Prime Hook, Delaware. The patterns among locations and tissues were not as clear for the other 

metals because the levels generally averaged below 100 ppb. The levels of contaminants found 

in horseshoe crabs, with the possible exception of arsenic in Florida, and mercury from Barnegat 

Bay and Prime Hook, were below those known to cause adverse effects in the crabs themselves, 

or in organisms that consume them or their eggs, even in relatively large quantities. These 

results indicate that site-specific data are essential for managers to evaluate the potential threat 

from contaminants to both the horseshoe crabs and to their consumers. 

4.2. Organic Compound Concentrations in Shorebirds and Horseshoe Crabs

Maghini (1996*) collected sand, horseshoe crab eggs, and ruddy turnstones, at 2 locations, Port 

Mahon and South Bower Beach, along the Delaware shoreline. Sites were selected to sample 

resident and migrant horseshoe crab populations, which could be exposed to different 

contaminant sources. Sediment and egg samples at each site were collected 1–4 June 1992 along 

10 (non-randomly selected) transects located perpendicular to the shoreline. Sand within 25 cm 

of the surface was collected at 10 stations along each transect. Horseshoe crab eggs were also 

collected along the 10 transects. Twenty-two turnstones were shot at Port Mahon, and none were 

collected from South Bower Beach. Chemical analyses were conducted by the Geochemical 

Environmental Research Group at Texas A&M University. Quality assurance measures were 

conducted by the laboratory and considered satisfactory. Many samples had concentrations of 

organic compounds that were below the limits of detectability. Maghini (1996*) found that 

concentrations of DDE and PCBs in turnstones were at background concentrations, but 2 

carcasses had concentrations of DDT that suggested recent exposure. Although concentrations 

of lead, mercury, and cadmium were detectable in sand and tissue samples, most were within 

background concentrations. Arsenic and selenium concentrations were elevated in turnstone 

tissues, but were similar to other species that fed on marine invertebrates and fish. Similar 

concentrations in horseshoe crab eggs suggest that they were the likely route of exposure. 

Conclusions were that concentrations of trace metals and organochlorines presented low 

toxicological risk. However, wider geographic and taxonomic sampling, component analysis of 

arsenic in eggs, and measurement of selenium concentrations in livers of turnstones were 

suggested. Little is known about chemical concentrations in shorebird wintering areas. 

4.3. Disease in Shorebirds

Piersma (1997) suggested that shorebirds may make a trade-off between investments in 

immunofunctioning and growth (chicks) or sustained exercise. Some shorebird species appear to 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 22 

be restricted to parasite-poor habitats (seashores, the arctic). Red knot chicks raised in the high 

arctic had daily energy expenditures that were 1.5x higher than temperate shorebirds of the same 

mass, yet grew at a faster rate. For migrant birds, optimal areas are separated seasonally by longdistances. If long-distance shorebirds are adapted to use parasite-poor habitats, they may be 

particularly susceptible to parasites and pathogens. Captive red knots only remained healthy 

after sea water was flushed through their holding cages, which suggested that they may be 

particularly susceptible to common avian pathogens. Figuerola (1999) found that haematoza 

infection rates in waterbirds, when controlling for phylogeny and population size, were greater in 

freshwater species than in those inhabiting saline habitats. Low reproductive success could be a 

cost associated with breeding in the climatically-marginal, but parasite-low, arctic. Increased 

adult survival afforded by inhabiting areas of low parasite loads may offset these costs. 

The Southeastern Cooperative Wildlife Disease Study (2002*) sampled 905 shorebirds from 

Delaware beaches in 2000 and 501 shorebirds (and 75 fecal samples) in 2001 for occurrence of 

influenza viruses. Virus was isolated from 5 species. The ruddy turnstone (n = 368) had the 

highest incidence rate (>13%), and lesser incidence rates (<5%) were found in red knots (n = 

620), dunlins (n = 164), semipalmated sandpipers (n = 107), and short-billed dowitchers (n = 68). 

Fecal samples collected off the ground in areas of turnstone activity revealed isolation of 5 

viruses. Preliminary results from 2002 were similar. One interesting note is that a turnstone in 

Delaware Bay that did not have the virus on 21 May tested positive when it was recaptured on 28 

May. 

In 1997, dead and dying red knots (46), white-rumped sandpipers (11), and sanderlings (3) were 

discovered in the area of Lagoa do Peixe, Brazil (Baker et al. 1998). All of the 35 collected 

knots were infected by hookworms (Acanthocephala spp.). About 150 knots found sick or dead 

in western Florida had their digestive tract infected by an unidentified sporozoan-type protozoan 

parasite (Woodward et al. 1977). Although no dramatic die-offs have been observed over the 

last 2 decades, information on parasite loads of Delaware Bay’s shorebirds is lacking and should 

be evaluated. Following Piersma’s (1997) hypothesis, Delaware Bay beaches could provide 

important, low-parasite environments needed by foraging red knots. 

4.4. Shoreline Changes in Delaware Bay

Shoreline habitat change can reduce horseshoe crab spawning habitat and consequently shorebird 

feeding habitat. Residential development along Delaware Bay’s beachfront can have negative, 

direct and indirect, effects on foraging and roosting shorebirds. Storm damage and longshore 

transport of sand can greatly affect beach characteristics. Bulkheads may block access to 

intertidal spawning beaches, and seawalls and groins can intensify local shoreline erosion and 

prevent natural beach migration (Atlantic States Marine Fisheries Commission 1998a*). Over 

the last 100 years, beaches in New Jersey have eroded at a rate of 0.3–3.7 m/year and in 

Delaware at a rate of 0.3–7.9 m/year (mean = 0.9–1.5 m/year, U. S. Army Corps of Engineers 

1991*, 1997*), and are presently at 2–6 m/year (Galofre 2002*). Increased turbidity, siltation, 

and peat exposure caused by erosion creates anaerobic conditions in horseshoe crab nests and 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 23 

reduces egg survivorship (Botton et al. 1988). Few crabs tend to spawn on beaches with much 

peat. Natural and human creation of inlets (e.g., Thompson’s and Moore’s Beaches) may have 

channeled crabs into marshes where they were harvested or failed to successfully reproduce (see 

<www.delawarebay.com>). Sand nourishment on beaches can increase habitat for spawning 

horseshoe crabs if sediment types match natural beaches favorable to breeding horseshoe crabs 

(see section 7.6). Monitoring and management of beach conditions will likely be needed to 

sustain habitats for spawning crabs and foraging shorebirds. 

4.5. Sea Level Rise from Global Climate Change

Galbraith et al. (2002) used U. S. Environmental Protection Agency data on historical sea level 

rise to predict sea level change at sites important to shorebirds. Assuming global temperature 

changes of 2o

C (50% chance) or 4.7oC (5%), resultant sea level rise would be 0.34 m (50% 

chance) or 0.77 m (5%). Local rates of historical sea level change were used with the Sea Level 

Affecting Marshes Model (SLAMM 4) to predict local effects of sea level rise by 2100. Based 

on historical rates, sea level in Delaware Bay would rise 0.3 m by 2100, with a 50% chance of 

rising 0.6 m. With these rates of sea level rise, tidal flats in Delaware Bay would decrease by 

23% under a historical rise and a predicted 50% chance of a 57% loss. A corresponding increase 

in salt marsh (.10%) would occur. These estimates do not account for any mitigation measures 

undertaken (e.g., seawalls). If losses of this magnitude occurred, Delaware Bay might not be 

able to support historical levels of shorebird use. Increased “storminess” associated with global 

climate change could further alter Delaware Bay’s shoreline habitats. 

4.6. Arctic Breeding Ground Conditions

Reproduction in arctic-breeding birds is known to be highly variable. Inter-annual variability in 

the reproductive success of shorebirds is usually attributed to weather or predation. Variability 

in predation on shorebird nests has been suggested as an indirect consequence of the cyclical 

abundance of lemmings. When lemmings are abundant, predators primarily rely on them as 

food; when lemmings are scarce, predators switch to other sources like birds. Blomqvist et al. 

(2002) used a 50-year series of fall banding data of red knots (C. c. canutus) migrating through 

the Baltic Sea in southern Sweden (Ottenby), and other information in the literature, to test the 

“bird-lemming hypothesis”. They predicted that: 1) juvenile red knot numbers would correlate 

with lemming fluctuations, 2) adult red knot numbers would not correlate with lemming 

numbers, and 3) post-breeding migration of adults would be earlier in years of high predation 

pressure. As an alternative hypothesis, they examined the correlation of climatic oscillations and 

breeding success. 

At Ottenby, Blomqvist et al. (2002) found no significant (P > 0.05) long-term trend in the 

number of adult or juvenile knots and no significant correlation between the annual numbers of 

adults and juveniles. Predation index from the Taimyr region of Russia was significantly and 

negatively associated with median knot passage date at Ottenby; proportional den use by foxes 

correlated with lemming abundance in arctic Russia. Predation index was significantly and 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 24 

negatively correlated with the number of juvenile knots captured at Ottenby, but not with the 

number of captured adults. Numbers of juveniles captured at banding stations in South Africa 

and Germany were also negatively associated with the predation index. Fourier analysis of the 

time series of juvenile captures revealed a periodicity of 3 years, which matched the median date 

of adult passage and lemming abundance in the Russian arctic. May weather did not correlate 

with any shorebird population variables. Blomqvist et al. (2002) found that patterns in Swedish 

knots were similar for curlew sandpiper (Calidris ferruginea) and likely extend to numerous 

other arctic-breeding species (see Underhill et al. 1993). Productivity of red knots and other 

shorebirds on eastern Southampton Island appears to be similarly correlated to abundance to of 

lemmings (P. Smith, Canadian Wildlife Service, unpublished data). 

Zöckler and Lysenko (2000) used a climate change model (HadCM2GSal), with a 1% increase 

of CO2/year, and Dynamic General Vegetation Models to examine effects of climate change on 

Holarctic waterbird populations. Of all biomes, tundra areas are expected to suffer the greatest 

climate-related habitat change. Major habitat changes for Calidris sandpipers, particularly in the 

low Canadian arctic, are predicted. Southampton Island is predicted to undergo major tundra 

loss, while part of northeastern Canada and Greenland are predicted to cool. Habitat changes 

have not yet occurred, but temperature changes are underway. Temperatures have risen by 1.3oC 

over the last 30 year at Resolute, Canada (Falkingham et al. 2001*). Mean July temperature in 

breeding areas was positively, but not significantly, correlated (r = 0.3) with the percentage of 

juvenile islandica red knots observed in the subsequent season on wintering grounds. Boyd 

(1992), however, suggested that a relationship existed between mean June temperature in 

northeastern Canadian arctic and the total number of knots observed in Great Britain the 

subsequent winter. More recently, Boyd and Piersma (2001) found that cold arctic summers 

affected both productivity and adult survival of knots wintering in Britain. 

Little information exists on the biology or productivity of rufa red knots on their breeding 

grounds. Knots (20 of 165) radio-tagged in Delaware Bay were relocated on breeding grounds 

on Southampton and Prince William Islands, Canada (Niles et al. 2001*). Knots tended to use 

low elevation, barren tundra located within 50 km of the coast. Eleven nests in sparsely 

vegetated tundra (e.g., eskers, frost boils), often associated with Dryas, were found in 2000. 

Topographical placement of nests may depend on the amount of snow cover when birds arrive, 

but nests are usually located #180 m of isolated wetlands. Nest density on Southampton Island 

ranged from 0.85 nests/km2

 in 2000 to 0.58 nests/km2 in 2002 (Niles et al. 2003*). No dramatic 

weather events occurred on Southampton Island during the breeding seasons of 1999–2002 (L. 

Niles, personal communication). 

4.7. South American Wintering Ground Conditions

In general, much of the Patagonia and Tierra del Fuego coast line is in good ecological condition 

(see descriptions at <http://www.ramsar.org> and <http://www.whsrn.org>). However, oil 

exploration and its associated infrastructure pose risks for migrant shorebirds that depend on 

intertidal feeding areas. Some wells have been placed in intertidal areas and development of oil 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 25 

industry infrastructure has lead to water and wind erosion of beach environments. Spills from oil 

storage and transfer facilities and oil tankers’ illegal ballast discharges are probably the greatest 

threat to migrant and wintering shorebirds. Although the region is still sparsely populated, much 

of the human population in concentrated in coastal areas, and pollution from untreated sewage is 

increasing and may have a future, negative effect on shorebirds. Season tourism brings needed 

cash to the region, but recreational beach activities (walking, shellfish collecting, vehicles, dogs) 

can disturb feeding and roosting shorebirds. Negative human disturbance effects are often 

greatest near cities. Installation of an ash plant (for the production of glass) could negatively 

affect shorebirds that use Bahía San Antonio Oeste. The plant could release $250,000 tons of 

calcium chloride into the bay annually, that could destroy the clams, mussels, oysters and other 

food sources upon which migrating shorebirds depend. Lagoa do Peixe is a large, shallow 

coastal lagoon in southern Brazil that has a highly variable, natural hydrology. Depending on 

rainfall and winds, the lagoon can dry up completely during the austral summer. Thus, shorebird 

use can be highly variable among years. Further north along the Maranhão coast of Brazil, 

shrimp farming could alter coastal systems in a way that is detrimental to migrant shorebirds. 

Despite potential threats, the southern wintering grounds of red knots do not appear to have 

changed dramatically in the last decade. 

4.8. Human Disturbance to Shorebirds

Nesting and migrant shorebirds are susceptible to disturbance caused by human activities. 

Human disturbance can force shorebirds to: 1) shift to feeding areas with fewer numbers of 

humans (Burger and Gochfeld 1991), 2) entirely abandon an area (Pfister et al. 1992, Smit and 

Visser 1993), or 3) increase vigilance, movement, or escape flights (flushing). Disturbance can 

therefore reduce feeding time and increase energy requirements at a time when migrant birds 

need fuel for migration (Hockin et al. 1992, Davidson and Rothwell 1993, Lafferty 2001). 

Distance to birds was the best measure of disruption to foraging sanderlings on California 

beaches (Thomas et al. 2003). Free-ranging dogs also disrupted foraging behavior and birds 

were completely excluded from beaches with intense vehicular use. The chronic disturbance of 

shorebirds can disrupt their behavior and cause them to use the energy they are trying to store for 

migration in an escape flight, thus affecting their energy balance and potentially their survival 

(Helmers 1992, Hockin et al. 1992, Davidson and Rothwell 1993, Harrington and Drilling 1996, 

Brown et al. 2001*, Gill et al. 2001, Lafferty 2001, West et al. 2002). 

Disturbance, frequently measured by flushing rate, has a greater effect on migratory bird species 

than on resident species (Burger and Gochfeld 1991). Anecdotal observations of shorebird 

researchers in Delaware (Carter et al. 2002*) and numerous published studies have noted 

negative human disturbance effects on shorebirds caused by: 1) walking and jogging (Burger 

1981), 2) windsurfing and hunting (Madsen 1998), 3) dog-walking, bird-watching, and shellfishing (Goss-Custard and Verboven 1993), 4) automobiles, boats and all-terrain vehicles 

(Rodgers and Smith 1997), 5) personal watercraft and outboard-powered boats (Rodgers and 

Schwikert 2002), and 6) aircraft (Koolhaas et al. 1993). Flushing distances have been shown to 

vary between types of disturbance, individual birds, and species. Researchers associated with 

national and regional shorebird conservation plans identified the high priority need to gain more 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 26 

information on how human disturbance affects shorebirds (Clark and Niles 2000*, Oring et al. 

2000*). 

Although no specific studies have been conducted to quantify disturbance effects to shorebirds 

in Delaware Bay, repeated disturbance along its beaches likely reduces shorebird feeding 

efficiency thereby increasing energy expenditure and reducing energy intake. Efforts to reduce 

and minimize human disturbance from recreational and commercial activities, and from research 

studies, in Delaware Bay are ongoing. New Jersey has implemented regulations which reduce 

the potential for disturbance associated with the horseshoe crab fishery by curtailing the hand 

harvest from its beaches. Bird observation platforms in New Jersey and Delaware have been 

built to allow for viewing of shorebirds with minimal disturbance. Actions have also been 

adopted to minimize any potential disturbance impacts of research associated with the catching 

and observing of shorebirds. 

4.9. Effect of Disturbance on Survival of Semipalmated Sandpipers

Pfister et al. (1998) present one of the few studies of a migratory species that demonstrates a 

relationship between body mass and annual return rate to a site of a migratory species. 

Semipalmated sandpipers were captured, color-marked, and measured during fall migration at 

Plymouth Beach. Massachusetts, in 1985 and 1986. Beaches was surveyed extensively during 

those 2 years for banded birds to determine the minimum length of stay for individuals. From 

Plymouth beach, semipalmated sandpipers are thought to make over-water crossings of >3,000 

km. Using body fat estimates, length of stay, and a linear regression model derived from 

sandpiper banding and recapture data at this site during the 15 years from 1971 to 1984, the 

authors calculated percent body fat of 255 individual sandpipers departing from the site. During 

1986 and 1987 surveys were conducted to determine how many birds banded the previous year 

returned to the site. A logistic regression model was used to relate return to the staging site (1 = 

return, 0 = no return) to the estimated fat levels at departure. Because of possible biases in the 

methods used to estimate fat at departure, an alternate method was also used to test the 

hypothesis that return rates are associated with fat levels. In this method, the authors used the 

difference between of actual length of stay and the time in days that would be needed to attain 

40% body fat (based on linear regression of fat deposition rates from previously collected data) 

as an index of the likelihood that birds would attain the desirable departure weight before 

migration. Birds were separated into 3 risk groups based on how many days short they were of 

attaining that level of 40% body fat. In both the estimated fat levels at departure and the risk of 

not attaining favorable fat levels at departure models, regression analysis revealed that fat level 

at departure had a significant association with return rate. The authors suggest that the 

association between fat levels and annual return rate is due to differences in return rates caused 

by fat depletion during the non-stop flight over water. The results support the idea that 

disturbance reducing the feeding efficiency of shorebirds at staging areas can reduce the ability 

of these migrants to attain high fat levels for their migratory flights and therefore may lead to 

their mortality. 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 27 

4.10. Horseshoe Crab Bait Landings

The Atlantic States Marine Fisheries Commission adopted a Fishery Management Plan for 

Horseshoe Crab in 1998. It limited landings in New Jersey, Delaware, and Maryland (in 

recognition of that these states had already acted to reduce harvest levels) to existing harvest 

levels, encouraged other states to reduce harvest, and recommended development of a coast-wide 

cap on commercial bait landings in 2000. Adopted in 2000, Addendum 1 established landings 

for the 1995–1997 reference period and state-specific 25% reductions in 2000 landings from the 

reference period (Atlantic States Marine Fisheries Commission 2000*). It was recognized that 

some states had already reduced harvest >25% below the reference period, and these states were 

encouraged to maintain their current reductions (about 211,000 crabs in Maryland and 297,680 

crabs in New Jersey). States that harvested <1% of the coast-wide landings were exempted from 

the 25% reduction (reviewed annually). In addition, Addendum 1 asked the National Marine 

Fisheries Service to establish a horseshoe crab sanctuary at the mouth of Delaware Bay. In 2001, 

the sanctuary was established and now protects 3,885 km2

 of crab habitat from harvest. Also in 

2001, Addendum II of the fishery management plan was adopted to establish procedures for 

inter-state transfer of harvest quotas (Atlantic States Marine Fisheries Commission 2001*). 

After adoption of Addendum I in 2000, coast-wide reductions in crab bait landings ranged from 

37 to 58%, and bait landings were reduced 34–75% in New Jersey, Delaware, and Maryland 

(Table 4.1). Some unknown portion of crabs that breed in Delaware Bay are likely landed in 

Maryland. Because horseshoe crabs have a delayed sexual maturity of about 9 years, changes in 

population size that resulted from increased harvest in the mid-1990s and subsequent restrictions 

not yet been realized. 

4.11. Changes in Horseshoe Crab Populations

The Atlantic States Marine Fisheries Commission Horseshoe Crab Stock Assessment Subcommittee (Millard et al. 2000*) recommended that 3 surveys, as interim measures until a stock 

assessment is completed (Atlantic States Marine Fisheries Commission 1998b*,c*), be evaluated 

to determine short-term trends of horseshoe crab populations: 1) re-designed Delaware Bay 

spawning survey, 2) Delaware trawl survey, and 3) National Marine Fisheries Service fall trawl 

survey. 

The Delaware Bay Horseshoe Crab Spawning Survey was substantially modified in 1999 to 

provide a statistically reliable survey of spawning crabs. In 2002, volunteers conducted 243 tidebased surveys on 23 beaches of New Jersey (10 beaches) and Delaware (13 beaches). An index 

of spawning activity is calculated as the number of spawning females within 1 m of high tide on 

beach index sites. Smith et al. (2002c) recommended that females be used to assess spawning 

activity because: 1) female abundance is the most direct measure of reproductive potential, 2) 

distribution of females is less variable than males, and 3) counting females alone is more costeffective. In 2002, spawning, which peaked in late May, tended to be somewhat higher in New 

Jersey than in Delaware (Smith and Bennett 2003*). Since 1999, spawning activity has 

remained unchanged in New Jersey (slope = 0.06, SE = 0.04, P = 0.29) and in Delaware (slope = 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 28 

-0.08, SE = 0.03, P = 0.16). Substantial shifts in spawning concentrations were noted from 

previous years. In 2002, for example, there were large increase in spawning activity on New 

Jersey beaches in the upper bay. Increases on some New Jersey beaches may or may not 

compensate for declines elsewhere. However, bay-wide spawning activity has been stable over 

the past 4 years, indicating some degree of compensation. Smith et al. (2002c) found that the 

number of sampled beaches and temporal stratification were the most important determinants of 

achieving the power needed to detect changes in spawning activity. 

The Delaware 30-foot trawl survey has been conducted consistently between March and 

December since 1990; horseshoe crab information is restricted to the April–July period. The 

State of Delaware has also conducted a 16-foot trawl survey, for the last 11 years, that targets 

juvenile (<160 mm wide) and young-of-the-year crabs. The National Marine Fisheries Service 

(NMFS; 2002*) has conducted a fall trawl survey along the Atlantic coast since 1977. 

Horseshoe crab information was restricted to the region between New York and Cape Hatteras, 

and only stations #27 m deep were used to calculate crab abundances. Gear for the NMFS 

survey changed dramatically over the course of a few years in the mid-1980s and invalidated 

analysis of the complete time series. Geometric means of annual all crab catches in the 30-foot 

trawl have decreased since 1990 (linear regression, R2

 = 0.661, P = 0.0007; S. Michels, 

unpublished data). Although counts in most recent years appear to be stable, the lowest recorded 

catch in 13 years occurred in 2002 (Figure 1). Also, mean catch per unit effort was significantly 

(P <0.025) lower in later years of the survey relative to the early 1990s (Table 4.2; Andres 

analysis). Although not significant, differences between periods were in the same direction as 

the 30-foot trawl survey for juvenile and young-of-the-year crabs in the 16-foot trawl and for all 

crabs caught in the NMFS fall survey (Table 4.2; Andres analysis; Figure 2,3). Note that the 

catch per unit effort for these latter surveys is very low. Horseshoe crab populations may now be 

stable but are likely at lower levels than in the early 1990s, and possible decreases may be 

apparent in all age classes of the population. Preliminary estimates from trawl surveys off of 

Delaware Bay (extending approximately from Ocean City, Maryland, to Atlantic City, New 

Jersey, and 22.2 km offshore) indicate a total population of 11,400,000 " 5,453,000 crabs (95% 

confidence interval), of which about 2.7 million are spawning age females (Berkson and Hata, 

unpublished data). The estimate of primiparus females ranges from 200,000 to 522,000 crabs. 

This does not include any animals within the Delaware Bay or animals beyond 22.2 km, assumes 

100% gear efficiency, and should therefore be considered a minimal estimate. Landings of 

female horseshoe crabs for the states of Delaware, Maryland, and New Jersey in 2002 totaled 

297,932 crabs, suggesting that the stock may be rebuilding as recruitment is exceeding landings 

in this area (but the 95% confidence limit of the estimate includes the landings value). 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 29 

5.0. ESTIMATES OF SHOREBIRD POPULATION SIZES AND TRENDS

5.1. Shorebird Population Sizes

 5.1.1. Coarse continental estimates

Morrison et al. (2001) compiled published and unpublished counts of shorebirds, by season and 

region, to generate coarse, flyway population estimates for North American-breeding shorebirds. 

They used the maximum summation of counts within a region to determine population size. For 

example, maximum counts of red knots at all sites on the Atlantic coast, during northward 

migration, would be summed to produce an estimate of that flyway’s population. All regions 

would then be summed to produce a continental estimate. These estimates were thought to be 

the minimum population present during the late 1980s and early 1990s. The method would 

likely only over-estimate population size, by counting individuals multiple times, if large 

numbers of the same individuals would stop at a few sites within the same region. Each estimate 

was assigned an accuracy (confidence) score which reflected quality and breadth of data used to 

generate the estimate. Of the 8 species considered in this report, populations in eastern North 

America range from 11,300 to 994,600 individuals (Table 5.1). Confidence in estimates for 

these species ranged from low to moderate. The population of rufa red knots was estimated to be 

170,000 (150,000 birds in eastern North America) in the late 1980s and was one of the smallest 

populations of red knots known to occur throughout the world (Piersma and Davidson 1992). 

 5.1.2. Re-sighting banded red knots in the 1980s

Between 1980 and 1987, Harrington (2002*) and his colleagues marked red knots with color 

bands in North and South America. Between springs of 1981 and 1990, Delaware Bay knots 

were scanned for color bands. This information allowed for calculation of the frequency with 

which birds of each band cohort (a group of birds banded at the same location in the same year) 

were found. This number, in combination with an estimate of annual survivorship of knots and 

known band cohort sizes, was used to estimate the population size as: [(number checked for 

bands*estimated number alive) ) number of cohort birds found]. The estimated number alive is 

the [(cohort size*( monthly survival rate* number of months since banding)]. The re-sighting 

rate was calculated as: {[(number of cohort-marked birds found ) expected cohort number alive) 

) number of birds checked for bands]*1000}. The expected cohort number alive was the 

original number banded in the cohort reduced to adjust for an annual survivorship of 0.752 

(details on model selection are not provided). A population estimate of red knots (rufa) made for 

each year was based on band re-sighting ratios of knots banded in Massachusetts during fall and 

re-sighted in New Jersey in spring, and on knots banded in New Jersey in spring and re-sighted 

in New Jersey in spring. Before estimates were calculated, cohorts were removed if <5 banded 

birds from a cohort were observed per 1,000 birds checked . This removed re-sighted cohorts 

where the original banding cohort was small. In addition, 2 cohorts were removed (banded on 

Delaware Bay in 1980 and 1981) where color band loss was a problem. Mean re-sighting rates 

of knots banded in Massachusetts and re-sighted in New Jersey were compared to that of birds 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 30 

both banded and re-sighted in New Jersey. The 2 groups were not significantly different (F-test, 

P > 0.05) and were therefore combined. Separate population estimates were calculated for each 

band cohort during each re-sighting year. For example, estimates, adjusted for survivorship, 

were made for a cohort banded in Massachusetts in 1984 and re-sighted in New Jersey 10, 22, 

34, 46, 58, and 70 months later. 

Annual population size estimates during 9 years between 1981 and 1990 ranged from 59,215 "

16,085 (1990) to 212,885 " 49,575 (1981). Ranges of the annual standard deviations of these 

estimates was 20–40% of their corresponding annual population estimate (Table 5.2) The overall 

mean of 28 separate estimates was 143,680 " 13,579 (SE). There was no population trend 

evident among the yearly estimates (R2

 = 0.003, P = 0.74). Note, however, that little is known 

of the size and annual variation of the non-breeding (presumably sub-adult) population, which 

evidently remains in South America and the southeastern U. S. during the northern summer. 

Some unknown portion of sub-adults visit Delaware Bay each spring. Finally, little is known of 

how the size of the non-breeding population relates to the size of the breeding population or to 

annual variation of breeding production. The mean re-sighting estimate of population size of 

knots in eastern North America in the 1980s was similar to the coarse estimate (see Table 5.1) 

generated by Morrison et al. (2001). 

 5.1.3. Red knot band re-sighting in South America

González et al. (2001*) color-banded 107 red knots in Rio Grande, Tierra del Fuego, Argentina, 

in December 2000 and used re-sighting information from there and Bahia de San Antonio (1,450 

km to the north), in early 2001, to estimate the population size of red knots wintering in southern 

South America. Scans of Rio Grande-banded birds re-sighted at San Antonio gave an estimate 

of the entire population wintering south of San Antonio stopover (in Rio Grande and Bahía 

Lomas) as 31,800 (95% confidence interval = 26,850–37,850). Scans of San Antonio-banded 

birds re-sighted at either site gave an estimate of 37,600 individuals, which was likely an 

estimate of the southern South American wintering population. This estimate corresponds fairly 

well with estimates from aerial surveys made during the same period (see section 5.2.1). If the 

current population of knots wintering in southern South America is about 30,000 individuals, and 

the population wintering in northern South America is about 15,000 birds (A. J. Baker, personal 

communication), then the total population of rufa red knots (. 45,000 birds) is probably 

substantially lower than late 1980s levels. Maximum counts on spring aerial surveys in 

Delaware Bay (see section 5.2.2) from 2000–2002 were lower than this estimated value (Table 

5.4). 

5.2. Shorebird Population Trends

 5.2.1. Aerial surveys of red knots in South America

Aerial surveys, usually with fixed-winged aircraft, were conducted along the southern South 

America coastline during the boreal winter 1982–86 (Morrison and Ross 1989a,b). The 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 31 

Argentine coast was surveyed in 1982 and Tierra del Fuego was flown in 1985. Flights, at high 

tide when possible, were made at an altitude of 50–80 m and 160 km/hour. The flight line was 

selected to survey the most important marine-influenced habitats and was usually 50 m offshore. 

Shorebirds were identified to species (except for small Calidris sandpipers) unless conditions or 

size of flocks prevented a reasonable assessment. Along the Atlantic coast of South America, 

red knots (n = 76,392 birds) were distributed among Tierra del Fuego (69.7%), the Argentine 

Patagonian coast (18.7%), northern Brazil (10.9%), and western Venezuela (0.7%). In Tierra del 

Fuego, the most important site was Bahia Lomas where 41,700 knots were counted (54.6% of all 

observations). Aerial surveys of the same shorelines of Tierra del Fuego were repeated with the 

same methods and same observers in 2000–2002. Counts of red knots made in Bahia Lomas, 

and for the entirety of Tierra del Fuego, in 2000 tended to be similar to counts made in 1982/85 

(Table 5.3). However, substantial decreases in knot counts, relative to 2000, occurred in 2001 

and 2002 (Table 5.3). A complete survey of Tierra del Fuego and the Patagonia coast in 2002 

indicated that knots did not re-distribute themselves at sites north of Tierra del Fuego (Table 

5.3). Numbers from Tierra del Fuego in 2003, although analysis is incomplete, suggest a slight 

increase from 2002 levels (R. I. G. Morrison, personal communication). Lack of a longer time 

series precludes a thorough analysis of this dataset. Ground counts and re-sighting information 

suggests that knot numbers at San Antonio declined from >20,000 in 1996 to 15,000 in 1997–

1998 and further to 8,500 ("500) in 2001. Because of relative stability on wintering grounds, 

continued surveys of southern South America could provide important information on knot 

population change. 

 5.2.2. Spring aerial surveys in Delaware Bay 

To determine shorebird use in Delaware Bay, weekly aerial surveys of the entire shoreline of 

Delaware Bay have been conducted, since 1986, by 2 constant observers, and 1 recorder, in a 

Cessna 172 (see Clark et al. 1993). Flights, at a height of 30 m above the shoreline, started at 

Cape May 3 hours after high tide, headed north along the New Jersey coast to the mouth of the 

Delaware River, and then turned south along Delaware’s shoreline to end at Cape Henlopen. 

Because little information exists on species-specific turnover rates, the maximum counts 

obtained during a single flight are used to determine changes in numbers in Delaware Bay. 

Yearly maximum counts are provided in Table 5.4. Using this method, Niles et al. (2003*) 

found that the maximum annual counts of red knots differed among recent years (1998–2002; 

Kruskal-Wallis, P2

 = 19.26, df = 5, P = 0.002). A decrease in maximum red knot counts was 

marginally significant (P = 0.068) from 1997 to 2002 (Andres analysis; Kendall’s nonparametric 

concordance test; Hollander and Wolfe 1973:185–199). The mean of maximum knot counts, 

however, did not differ between 1986–1996 and 1997–2002 periods (Table 5.5). No other 

species showed consistent declines, but maximum counts of dunlins and dowitchers have 

increased significantly in recent years (Table 5.5). Because of their unknown relationship to real 

population size, maximum aerial survey counts are not be useful to determine population change. 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 32 

 5.2.3. International and Maritime Shorebird Surveys

Bart et al. (2003*) used data from the Maritime Shorebird Survey (MSS) and the complementary 

International Shorebird Survey (ISS) data to assess trends in migrant shorebird numbers along 

the north Atlantic coast (from Georgia to Newfoundland). The primary purpose of these surveys 

is to document abundance and distribution of migrant shorebirds. Volunteers visit sites every 

10–14 days, when shorebirds are present in the site’s region, and count all shorebirds. ISS 

guidelines ask that counts (or estimates) of all shorebird species be made once each third month 

(once between the 1st and 10th, once between the 11th and 20th, and once after the 20th) during 

spring (1 April–10 June) and fall (10 July–31 October) migration. Migration periods were 

defined for each species by determining the 20th and 80th percentiles of the cumulative 

distribution of spring and fall periods. A linear model was used to determine site-specific rates 

of change in shorebird numbers, for sites that had >3 visits, and were combined to determine an 

average rate of change. Only species that were observed at $8 sites were included in the 

analysis, and highly significant outliers (residual P < 0.005) were removed from the analysis. 

Morrison and Hicklin (2001*) independently used average counts at “paired” Canadian Maritime 

sites to make comparisons between decades (1970s, 1980s, and 1990s). They reported the sign 

of the difference (negative or positive) and the significance (P-value) of the difference. Bart et 

al. (2003*) found that knot counts declined, but not significantly (P > 0.1), at a rate of 

1.65%/year in eastern North America. Sanderling, semipalmated sandpiper, and least sandpiper 

all decreased at significant rates (.4–7%, P <0.05) in the ISS/MSS analysis (Table 5.6). Red 

knots and semipalmated sandpipers were the only species that showed consistent, negatives 

changes among time periods and analysis methods (Table 5.6). In a previous analysis of ISS 

data, sanderlings had decreased substantially (Howe et al. 1989). P. Hicklin (unpublished data) 

has found a shift in the distribution of bill lengths of semipalmated sandpipers captured while 

migrating through the Bay of Fundy, Canada. Proportionally fewer long-billed birds, those from 

the most eastern population that use Delaware Bay in the spring, have been captured in recent 

years. 

 5.2.4. Quebec migration checklists

Since 1950, opportunistic information has been collected from daily checklists of volunteer 

birders in Quebec. These records have been computerized and were used by Aubry and Cotter 

(2001*) to assess the population trends of fall-migrating shorebirds in the province. They used 

the frequency of occurrence of shorebird species occurrence on checklists, from 1976 to 1998, to 

determine if reporting rates changed through time. From this analysis, significant decreases were 

found in reporting frequencies for ruddy turnstones, red knots, and semipalmated sandpipers 

(Table 5.6). Decreases in the latter 2 species are consistent with ISS/MSS analyses. 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 33 

6.0. IMPORTANCE OF DELAWARE BAY TO SHOREBIRD POPULATIONS

Harrington (2002*) compared 8 years of population estimates of red knots in the in the 1980s 

(see section 5.1.2) to aerial surveys conducted during the same period (see section 5.2.2). A 

consistent relationship between the maximum count and the population size would only exist if a 

constant proportion of the spring migrating knot population uses Delaware Bay each year. No 

significant relationship (r = 0.27, P = 0.51) existed between annual estimates of population size 

determined from color-banding ratios and maximum counts from annual spring aerial surveys. 

On average, the maximum aerial survey count represented 38% of the adult population size 

estimates from the same 8 years and ranged from 14 to 77%. Therefore, Delaware Bay is likely 

not used by a consistent proportion of the knots each year, and use varies considerably among 

years. Note that the error for population estimates is relatively high (see Table 5.2). 

Harrington (2002*) also used counts made between 1974 and 2000 by ISS cooperators to 

compare numbers of shorebirds at Delaware Bay to other Atlantic coastal regions (see section 

5.2.3). From these counts, the maximum value of all counts of each species from Atlantic 

marine locations was determined for spring and fall migration periods. To compare Delaware 

Bay to other Atlantic locations, maximum counts made during 17 years of aerial surveys of 

Delaware Bay (see Clark et al. 1993) were divided by the sum of maximum counts made at sites 

surveyed by the International Shorebird Surveys (ISS). There were 483 Atlantic coast locations 

visited (13,987 surveys) during fall migration and 259 visited during spring (5,795 surveys); 19 

of the locations visited during fall were on Delaware Bay. Maximum counts from these 

Delaware Bay sites were summed to provide an overall index for the bay. Because of 

duplication with aerial surveys, ISS counts made during spring at sites on Delaware Bay were 

excluded from evaluation. Delaware Bay provides important habitat to some migrant shorebirds 

during fall migration, but is particularly important in spring (Table 6.1). Aggregations in 

Delaware Bay were greater during spring than fall across all species, and were dramatically so 

for all species except dowitchers (Table 6.1). The difference between proportional use in spring 

and fall might be attributable to the fact that there were data from aerial surveys of Delaware Bay 

during the spring but not during the fall. However, locations covered by the ISS in the fall 

included all of the well-known shorebird sites on Delaware Bay. The differing methodology 

does not seem to explain the large seasonal differences. Even if the method did confound 

interpretation of results, it could not explain the seasonal shifts of relative occurrence between 

species. For example, turnstones, knots and sanderlings were virtually absent from Delaware 

Bay during fall, whereas semipalmated sandpipers, dowitchers and dunlin were conspicuously 

present during both seasons. Clearly, Delaware Bay is critical spring stopover for many 

shorebirds, and >50% of the flyway populations of ruddy turnstones, red knots, and 

semipalmated sandpipers may use Delaware Bay beaches. Reliable estimates of turnover rates 

could show an increased importance of Delaware Bay to these species. The comparisons 

described above are probably the most reliable, minimal estimate of use of Delaware Bay by 

migrant shorebird populations. 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 34 

7.0. HABITAT USE BY SHOREBIRDS AND HORSESHOE CRABS

7.1. Shorebird Use of Marine and Non-marine Habitats

Harrington (2002*) used counts made between 1974 and 2000 by ISS cooperators to compare 

use of marine and non-marine sites along the Atlantic coast (see section 5.2.3). Survey sites 

were classified as primarily either marine or non-marine habitats and the average number of 

birds recorded during surveys was computed for northward and southward migration. Ruddy 

turnstones, red knots, sanderlings, dunlins, and short-billed dowitchers were all more abundant in 

marine than non-marine habitats during northward and southward migration (Table 7.1). 

Semipalmated sandpipers were more abundant in marine habitats in fall, but were equally 

abundant between marine and non-marine habitats during spring. Long-billed dowitchers and 

least sandpipers were equally abundant in both habitat types during both seasons (Table 7.1). 

7.2. Red Knot Habitat Use and Movements in Delaware Bay

Meyer et al. (ND*) radio-tagged red knots taken from cannon-net catches on New Jersey beaches 

15–19 May 1997 (5 birds) and on New Jersey (30 birds) and Delaware (20 birds) beaches 2–21 

May 1998. Telemetric searches for radio-tagged birds were conducted from the ground 16–30 

May in 1997 and from the ground and air 3 May–9 June 1998. Pre-determined ground locations 

were surveyed in New Jersey and Delaware; transmitter range averaged 1.6 km on the ground 

and 8 km in the air. Habitat, home range (kernels), and behavior was measured for each bird. 

Mean minimum duration of stay (calculated as the difference between initial capture day and day 

of last detection) in 1998 was 17 " 8 days (" SD, n = 47 birds) and ranged from 1 to 35 days. 

Birds may have been present in the bay for an unknown number of days before capture. Radiotagged birds preferentially used the lower, rather than upper, Delaware Bay region (P2

 = 317, df 

= 4, P = 0.001). The greatest number of radio-tagged birds were located in New Jersey on 16 

May, whereas the greatest number of birds was detected in Delaware in 23 May. Radio-tagged 

birds were not distributed evenly among all beaches and marshes and were concentrated on a few 

beaches throughout the bay (P2 $179, df $ 22, P = 0.001) and also within each state. Radiotagged red knots commonly crossed Delaware Bay; in 1998, 60% of radio-tagged knots made $1 

bay crossing. The number of bay crossings an individual knot would make was independent of 

initial weight, banding date, minimum duration stay, capture location, number of re-sightings, or 

any interactions. Frequency of bay crossings increased at the end of the May. Knots moved on 

average 27.4 km (SD = 16.8). Significantly more knots were located on beaches than in marshes 

(P2

 = 4,797, df = 1, P < 0.0001), and most knots were found on sandy beaches (79% of beach 

detections). 

7.3. Shorebird Habitat Use on Cape May Peninsula, New Jersey

Burger et al. (1997) chose representative (non-random) marshes and beaches along the Atlantic 

and Delaware Bay coasts of New Jersey to determine shorebird numerical and behavioral use; 

the magnitude of shorebird use was a consideration in selection. Scan samples of shorebirds (20 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 35 

minutes) were made from 22 May to 4 June, 1991–92, at 2 Atlantic Ocean marshes and 1 (each) 

marsh, mudflat, and beach along Delaware Bay. Surveys occurred during different tidal stages. 

Scans were considered independent (with no to few replicates in space) and multiple regression 

procedures (arc-sine transformations) were used to construct habitat models. Univariate tests 

(Kruskal-Wallis) were used to determine significance of individual variables. Burger et al. 

(1997) found that location, date, tide, time, species, and location-tide interaction were significant 

in explaining differences in the proportion of shorebirds that were alert, feeding, or resting. 

Shorebirds fed mainly on falling, low, and rising tides. More birds fed in marshes and on 

mudflats than on beaches, and a higher proportion of birds fed during the middle of migration 

than at the beginning or end. The mudflats had the highest number of birds and the greatest 

proportion of feeding shorebirds. Location was the most important factor that explained 

differences in feeding within species. Ruddy turnstones and red knots were found in greater than 

expected proportions in Atlantic marshes. The greatest number of semipalmated sandpipers, red 

knots, ruddy turnstones, and sanderlings foraged on a rising tide. They conclude that migrant 

shorebirds use a mosiac of habitats on the Cape May Peninsula, and that habitat switching likely 

occurs because of the need to feed. 

7.4. Shorebird Beach Use in Delaware

Carter (2002*) used information opportunistically collected during field work to generate a 

preliminary map of beaches that supported the greatest numbers of red knots and ruddy 

turnstones in Delaware. Beach use was grouped into 4 categories: 1) extremely high use—large 

flocks at all weather conditions, 2) high use—large flocks in mild weather conditions, 3) 

moderate use—occasional large flocks intermittently, and 4) occasional use—some individuals, 

not regular. These criteria were applied to a 77-km length of shoreline between Woodland 

Beach and Cape Henlopen. Extremely high or high use beaches constituted 14% of the shoreline 

for red knots and 19% of the shoreline for ruddy turnstones (Table 7.2). Knots may distribute 

themselves among Delaware beaches in response (negatively) to on-shore wind speed. Carter 

and Scarborough (2002*) found that when average winds were >6.4 km/hour (over a 24-hour 

period measured at 5-second intervals), resultant wave heights deterred crab spawning and 

shorebird feeding on Delaware beaches. Information from radio-tagged knots is consistent with 

shorebird beach use data from Delaware and suggest that large aggregations of shorebirds are 

concentrated on a relatively small amount of Delaware Bay shoreline. Delineation and 

maintenance of high quality beach habitats for spawning crabs and foraging shorebirds is needed 

to ensure their long-term conservation. 

7.5. Influence of Beach Characteristics on Horseshoe Crab Reproductive Activity 

Smith et al. (2002b) surveyed 8 beaches each in New Jersey and Delaware to enumerate numbers 

of spawning crabs and deposited eggs. Beaches were selected in a stratified, random design 

based on (Smith et al. 2002c). For eggs, 5-cm cores were taken within a 3-m strip centered on 

the mid-beach elevation located along a 100-m segment of beach. At 40 locations on each 

beach, 2 core samples were taken (0–5 cm and 5–20 cm). Eggs sampled 24–25 May and 14–15 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 36 

June, which corresponded to heaviest spawning in 1999, were used to calculate density. 

Spawning crab surveys follow a bay-wide procedure that uses a stratified randomization with 

beaches, times, and quadrats as sampling units. Temporal strata were 5-day periods around new 

and full moons in May and June. Beach lengths varied 200–1,000 m and were surveyed at night 

(the higher of the daily tides). Systematically placed quadrats, with random starts, of 1 m2 were 

used to count spawning female crabs. A sub-sample from each beach that overlapped with egg 

sampling was used to compare spawning crab density and egg density. Egg clusters were 

sampled across the entire beach where crabs were observed spawning to determine spatial 

distribution of eggs. Beaches were ploughed by a tractor in Delaware to determine distribution 

of eggs clusters. Beach slope was incorporated into regression tree models, and Spearman rank 

correlations were also used. 

Smith et al. (2002b) found that correlations between cumulative densities of spawning crabs and 

deposited eggs (total and surface) varied among time and beach. The interaction of wave action, 

beach morphology, and beach location has a large effect on the number of eggs that remain on a 

beach. Certain beaches could be critically important to shorebirds. Horseshoe crabs appear to 

prefer low-energy, sandy beaches. High, wide low-tide terraces dissipate wave energy and create 

narrow, steep beaches. Previously, Botton et al. (1988) had surveyed 80 km of New Jersey 

beaches in Delaware Bay and found that only a moderate percentage of the shoreline provided 

optimal (10.6%) or suitable (an additional 21.1%) spawning habitat for horseshoe crabs (31%, 26 

km). Changing beach morphology could explain crabs spawning in tidal creeks. Association 

between beach morphology and live eggs on the surface was strong especially in late May. 

Distribution of eggs across beach foreshore was wider than previously reported. Egg distribution 

widened and became more uniform as the season progressed. They suggest that egg availability 

is not a simple function of number of females (but would be a minimum). 

 7.6. Beach Nourishment and Habitat Restoration for Crabs and Shorebirds 

Because the value of beach nourishment may depend on beach geometry and type of sediment 

application, Smith et al. (2002a*) evaluated the response of spawning horseshoe crabs to 

nourishment treatments in Delaware. About 2.294 million m3 of sand have been placed on 

Delaware Bay beaches in Delaware over the last 40 years. Re-nourishment efforts in New Jersey 

are less intense than in Delaware. Two beaches selected for nourishment were compared to 2 

un-nourished beaches in a controlled before-after design in 2001–2002. Coarse-grained 

sediment, topped by a layer of pea gravel, were added to treatment beaches. Counts of spawning 

crabs and sediment cores were taken, following methods outlined by Smith et al. (2002b) above, 

at each treatment and control beach. Analysis of Variance was used to compare treatment and 

control groups. Topographic features of the beach were measured, and egg pouches were placed 

in beach sediments at 3 tidal elevations to determine moisture content. May crab spawning on 

nourished beaches increased between 2001 and 2002, whereas spawning decreased in control 

beaches. Spawning declined on all beaches in June but was most dramatic on control beaches. 

May total egg density on nourished beaches dramatically increased between 2001 and 2002, 

whereas increase on the control beach (egg counts were only made on 1 control beach) were less. 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 37 

Egg density was substantially lower in 2002, relative to 2001, on all beaches. Beach 

characteristics, which influenced sediment moisture levels, affected egg development and 

viability. As preliminary conclusions, the authors suggest that nourishment can have a positive 

effect on horseshoe crab spawning if: 1) small volumes of nourished sediments are added that do 

not sufficiently alter beach slope, and 2) the application reflects a coarse estuarine beach that 

includes fine-grained sediments, gravel, and sand grains 0.35–0.50 mm in diameter. More 

information is needed to assess optimum size of fill materials and timing of operations. 

7.7. Shorebird Habitat Use in Relation to Beach Characteristics and Abundance of 

Horseshoe Crabs and Their Eggs

Botton et al. (1994) selected (non-randomly) 7 beaches along the New Jersey coast of Delaware 

Bay to survey shorebirds, adult horseshoe crabs, and horseshoe crab eggs. Shoreline sites were 

selected to represent typical beach habitat types and varied in structure and amount of 

disturbance. Shorebirds were counted at sites, a variable number of times, at diurnal low, high, 

and mid-tide periods between mid-May and early June; small calidrids (virtually all 

semipalmated sandpipers) were combined as peeps to produce the metric of birds/observer/hour. 

Adult horseshoe crabs were counted in 3 ways: spawning crabs along transects parallel to the 

shoreline (high tide), nest bowl depressions created by spawning females (low tide), and stranded 

crabs (low tide). Sediments were sampled during 2 periods from late April to early May and 

from mid-May to early June, on 2 non-random transects perpendicular to the shoreline from 

mean low water to spring high tide, at 3-m interval stations on transects, and at 2 depths (0–5 cm 

and 15–20 cm). Numbers of all developmental stages of horseshoe crabs were counted and sand 

grain size was determined. Beach slope, beach width (mean low water to spring high tide), 

presence of sand dunes, proximity to salt marshes, and degree of human disturbance were also 

measured. 

Red knots, ruddy turnstones, sanderlings, and small Calidris sandpipers (virtually all 

semipalmated sandpipers) constituted $98% of Botton et al’s. (1994) observations. Abundance 

of shorebirds, adult crabs, and egg densities varied among beaches. No direct, statistical 

comparisons were made between shorebird density and beach characteristics or horseshoe crab 

adult/egg abundance. The authors concluded that grain size was not a good predictor of site 

selection in shorebirds, and that horseshoe crab egg density alone did not predict shorebird 

abundance. Confounding factors include competition with gulls and that the food resource may 

be super-abundant (i.e. not limiting). Few other invertebrate foods were found in sediment 

samples, and a previous study (Botton 1984) found that bird predation did not deplete 

populations of a small bivalve. They suggest that shorebirds might be choosing beaches near salt 

marshes for supplemental feeding and roosting, or beaches where artificial or natural structures 

trap the longshore drift of horseshoe crab eggs. 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 38 

8.0. ABUNDANCE AND TRENDS OF HORSESHOE CRAB EGGS

8.1. Bay-wide Egg Density in 1999

Pooler et al. (2003) collected sediment on 2 days in May and 2 days in June 1999 on 16 

beaches—8 in New Jersey and 8 in Delaware. Sediment was collected by 5-cm diameter cores 

within a 3-m wide strip along a 100-m segment of beach; the strip was centered on the midbeach. One core to 5 cm (shallow) and 1 core to 20 cm (deep) were collected at 40 randomly 

selected locations in each strip. Median densities were 3 (shallow) and 275 (deep) eggs/core; 

numbers per core are translated into densities (eggs/m2) in Table 8.1. May density in shallow 

sediments was highly variable among beaches and ranged from 0 to 14,000 eggs/m2. Total egg 

densities on Reed’s Beach were lower in 1999 than 1990, but surrounding beaches in 1999 had 

similar egg densities as Reed’s in 1990. 

8.2. Egg Density on Delaware Beaches

During May 2001, Weber (2001*) sampled 8 beaches in Delaware on the new and full moons to 

determine horseshoe crab egg density. Two transects, placed perpendicular to the beach from 

foot of the beach up to 83% of the distance to the nocturnal high-tide wrack line were placed at 

each site (previous work has indicated all eggs were laid in this zone). Twenty-five cores (5.7-

cm diameter by 20-cm length) were systematically sampled across these 2 transects at depths of 

0–5 cm and 5–20 cm. Eggs were separated and either directly counted or estimated by volume. 

The extent of horseshoe crab spawning areas were delineated on each beach. Mean density of 

eggs for each transect was used to determine total egg load on each beach. Although Weber had 

sampled other beaches in previous years, information was not comparable because: 1) methods 

were altered in the period (from horizontal transects to vertical transects), 2) egg data were 

pooled across the entire April–July period, and 3) several beaches were nourished between 

sampling periods (studies were designed to determine effects of nourishment, see section 7.6). 

Densities in shallow sediments in May 2001 ranged from 873 to 530,000 eggs/m2

, and 

percentage of total eggs in shallow sediments ranged from 4 to 50% (Table 8.2). Only 3 of 8 

beaches had densities that were >100,000 eggs/m2 on either May sampling date. Repeated 

surveys of shallow egg abundance across the entire season at Port Mahon (a beach that did not 

undergo nourishment treatments) were similar among years [473,000 eggs (1999); 403,000 eggs 

(2000); 501,000 (2001); Weber 2002*]. 

8.3. Changes in Egg Density on New Jersey Beaches

Botton et al. (1994) reported that surface egg density, in the mid-beach, reached 104

 to 105

eggs/m2

 in the early 1990s (see section 7.7 for details). Following their “pit” methods, Niles et 

al. (2003*) surveyed horseshoe crab eggs on 6 beaches in New Jersey (Moore’s, Reed’s, Cook’s, 

Kimble’s, Norbury’s Landing, and Villas). Six samples, spaced 3-m apart were taken weekly (2 

transects) across the tidal gradient on each beach. Nonparametric tests (Kruskal-Wallis) were 

used to determine differences among years. The number of horseshoe crab eggs in shallow 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 39 

sediments (0-5 cm) was not evenly distributed among years (P2 = 39.95, df = 2, P < 0.001). By 

2002, Niles et al. (2003*) reported densities of $10,000 eggs/m2

on fewer beaches (P2 = 15.32, df 

= 2, P < 0.0005) and for a shorter time (P2, P < 0.0001). However, detailed information was not 

presented on changes in beach habitats during this period, egg densities on individual beaches, or 

parametric variance calculations provided in tables. Because egg density is known to be highly 

variable within and among beaches, additional details on methods and analytical calculations are 

needed before these data can be interpreted. 

8.4. Egg Abundance Sampling Design Considerations

Pooler et al. (2003) addressed 3 specific questions needed to develop a statistical design to 

estimate the quantity of horseshoe crab eggs: 1) how many sediment samples are needed per 

beach segment, 2) is egg density in a segment representative of the entire beach, and 3) how 

many beaches are needed to estimate bay-wide density. Questions considered eggs in shallow 

(0–5 cm) and deep (0–20 cm) sediments (see section 8.2). Program TRENDS was used to 

determine power of detecting a decline at various coefficient of variation levels and a Type I 

error rate of 0.2. A sample size of 40 sediment cores was sufficient for estimating and 

monitoring density of eggs 0–20 cm deep within a 100-m beach segment. However, a larger 

sample size (60 sediment cores) would be needed for estimating and monitoring density of eggs 

0–5 cm deep within a segment of beach. At most beaches, observed egg densities within the 

100-m segment were not representative of egg densities throughout the larger beach. On only 2 

of 6 New Jersey beaches did observed egg density fall within the inter-quartile range of beachwide densities. Variability in egg densities among beaches tended to be higher in June for 

shallow (CV = 0.43) and deep (CV = 0.29) sediments than in May (CV = 0.33, 0.26). A twostage (segment, cores) approach to sampling egg density is suggested. At least 10 segments per 

state would be needed to achieve a CV of 0.3 in shallow sediments. 

9.0. SHOREBIRD DIET AND USE OF HORSESHOE CRAB EGGS

9.1. Shorebird Diet in Delaware Bay

Tsipoura and Burger (1999) collected gut samples from >100 shorebirds by stomach flushing 

during May 1996 and 1997. These samples were analyzed under a microscope to determine the 

type of prey that the birds ingested, and proportional composition was determined through 

volumetric measures. Horseshoe crab eggs were found in guts of all shorebird species captured 

on the mudflats and beaches of the Cape May Peninsula. For beaches on Delaware Bay, 

horseshoe crab eggs ranged about 95-100% for red knots (n = 21), 100% for ruddy turnstones (n

= 6), 95–100% for sanderling (n = 13), 80–90% for semipalmated sandpipers (n = 30), and 60–

100% for least sandpiper (n = 12) of invertebrate remains in the gut. Lower numbers of eggs 

were found in birds captured while foraging in the marsh (semipalmated sandpipers and least 

sandpipers) and along the Ocean shore (sanderlings). Worms, insects and detritus made up a 

higher percentage of gut contents in those habitats. Sand was ingested by all species in all 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 40 

habitats, indicating that it might be important in the digestion process. There were higher 

concentrations of horseshoe crab egg membranes in all gut samples collected in 1996 compared 

to 1997. Conversely, sanderling semipalmated sandpiper, and least sandpiper samples in 1997 

had higher percentages of worms than in 1996. 

9.2. Stable Isotope Analysis Confirms Shorebird Dependance on Horseshoe Crab 

Eggs in Delaware Bay

Haramis et al. (2002*) used stable isotope technology to establish the unique isotopic signature 

of horseshoe crab eggs and developed methods to determine the signature in shorebird tissue. 

Blood plasma was used because of rapid turnover that would yield a local diet-related stable 

isotope signature. Eggs and other invertebrate shorebird foods were sampled. Feeding trials of 

penned red knots and ruddy turnstones were also conducted to determine consumption rate, diettissue fractionation, and mass gains of birds fed only horseshoe crab eggs. The horseshoe crab 

egg signature was well-separated from other invertebrate foods (e.g., blue mussels, sand shrimp, 

amphipods) and would be traceable in shorebird tissue. Carbon and nitrogen plasma stable 

isotope signatures of red knots (n = 48) were centered around the horseshoe crab egg value. 

Variability in isotope values was likely due to some consumption of non-egg invertebrate foods. 

Regression of the plasma nitrogen with body mass converged on the crab egg value. Body mass 

was a strong correlate of feeding time on crab eggs (n = 42). Knots held in a pen (n = 10) 

initially lost weight (first 9 days in captivity) and then entered a 13-day period of rapid weight 

gain; birds gained an average of 33.5 g (29.4%) of body weight during this period. Birds fed 

horseshoe crab eggs ad libitum during daylight conditions consumed an average of 18,000 

eggs/day. On Delaware Bay beaches, this translates to about 1 egg/second for a 5-hour period. 

One bird, the lightest at capture, gained 50% of its body weight over 13 days. Mass gains of 

captive birds exceeded 6 g/day, a rate comparable to that measured in live-trapped birds in 

Delaware Bay. These findings clearly demonstrate the red knot dependence on horseshoe crab 

eggs by convergence of isotope signature to the egg value, weight gains correlated with time 

feeding on crab eggs, and weight gains of caged birds solely fed crab eggs matched rate of 

weight gain in free-living knots. Data is currently being analyzed for other species (ruddy 

turnstones, semipalmated sandpipers, and least sandpipers). 

9.3. Functional Responses of Shorebirds Feeding on Horseshoe Crab Eggs

Stillman et al. (2003*) measured the feeding rates of shorebirds in response to horseshoe crab 

egg density. Eggs were mixed with sand in a shallow tray (.0.3 m2

, 2-cm deep) and presented to 

shorebirds in situ on Delaware beaches. Egg density in treatments varied from 300/m2

 to 

25,000/m2. Foraging behavior of focal shorebirds was video-recorded for 5 minutes after the 

first bird entered the tray area. All interactions between birds were recorded. The numbers of 

shorebirds in the tray were counted at 15-second intervals. After 5 minutes, the tray was 

retrieved and the sand-egg mixture removed for later separation. Attack rate, assessed by each 

time a bird pecked the sand surface, was calculated, during the first 1 minute of the tape, for 

dunlins, semipalmated sandpipers, and red knots. Densities of birds feeding within and outside 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 41 

of trays were thought to be similar, and the average density of feeding shorebirds during the 5-

minute interval was positively, linearly correlated to egg substrate density (P < 0.001). After 5 

minutes, birds tended to deplete about 80% of the eggs, regardless of either species or egg 

density. Pecking rates were similar among species (1.7/second for semipalmated sandpipers; 

2.0/second for red knots and dunlins) and did not vary with egg density (linear regression; n = 

30, 28, 11; P > 0.05). Because direct consumption could not be measured, the probability of 

consuming an egg given a peck was calculated by determining the total number of pecks in each 

experiment (the number of bird seconds*species-specific pecking rate) and the number of eggs 

per peck (total number of eggs consumed/total number of pecks). The number of eggs per peck 

increased from near 0 to 1 when density was >10,000 eggs/m2 and was described as p = 

(pmax*E)/(E50+E), where p = number of eggs consumed per peck, E = initial egg density, E50 = 

egg density at which p is 50% of pmax. Values were estimated as 3,355 ( E50) and 1.3 (pmax) 

from non-linear regression (P < 0.05). The number of eggs consumed per peck was not 

influenced by species composition on the feeding tray. Feeding rate (F) of each species was 

calculated as: F = aE/(1+aEH), where a = area search rate (m2

/second) and H = handling time. 

Estimates of a and H from non-linear regression were: 0.00069 m2

/second and 0.45 second for 

semipalmated sandpipers; 0.00083 m2/second and 0.38 second for dunlins; and 0.00094 

m2

/second and 0.38 second for knots. Interference was not included in the model, and data 

supported the rarity of aggressive interactions among feeding shorebirds. Feeding rate for all 3 

shorebirds showed a similar positive, logarithmic relationship with egg density. At the highest 

egg densities (25,000 eggs/m2), shorebirds fed at a rate of 2 eggs/second. Despite vast body size 

differences of the 3 shorebird species, feeding rates were similar. Maintenance of a feeding rate 

of 1 egg/second for 5 hours would lead to a daily consumption similar to estimates from feeding 

trials of penned knots (18,000 eggs, see section 9.2). Because energy expenditures are related to 

body mass, then mass gain beyond maintenance in larger-bodied birds (e.g., red knot) might only 

be possible if horseshoe crab eggs are available in high densities. Knots should be the first 

species to exhibit reduced mass gains if horseshoe crab egg abundances are reduced. 

9.4. Competition Between Shorebirds and Gulls for Horseshoe Crab Eggs

Gulls foraging on the beaches of Delaware Bay may directly or indirectly compete with 

shorebirds for horseshoe crab eggs. Burger et al. (1979) found that intraspecific aggressive 

interactions of shorebirds were more common than interspecific interactions. Negative 

interactions between knots and laughing gulls that resulted in disruption of knot behavior were 

no more prevalent than interactions with ruddy turnstones, dowitchers, or black-bellied plovers 

(Pluvialis squatarola). However, larger bodied species tended to successfully defend areas 

against smaller species. Total aggressive interactions increased as density of birds increased in 

favored habitats, which indicated some competition for food resources. Sullivan (1986) found 

that aggression in ruddy turnstones increased as experimentally-manipulated food resources 

(horseshoe crab eggs) changed from an even distribution to a more patchy distribution. 

Decisions to defend food patches were likely driven by the cost of locating new patches. 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 42 

Following upon earlier results, Burger et al. (2003*) studied foraging behavior in shorebirds and 

gulls at Delaware Bay, New Jersey, during spring migration to determine if interference 

competition existed between shorebirds and gulls. They tested the hypothesis that vigilance and 

aggression rates (and thus foraging rates) were directly related to the size of the species of the 

nearest neighbor to foraging shorebirds. Thus, they make the prediction that vigilance and 

aggression rates will be greater when a shorebird's nearest neighbor is a gull, and that foraging 

rates are lower when the nearest neighbor to a shorebird is a gull. Interference competition 

occurs in foraging flocks if there is a change in feeding rate of a focal bird when it feeds in the 

presence of different numbers of competitors, or with different species. In general, shorebirds 

have conspecifics as their nearest neighbors and, thus, fed in conspecific groups. Similarly, 

laughing gulls usually fed among conspecifics. 

The species of nearest neighbor has a significant effect on time spent foraging and number of 

pecks (per 30 seconds) of ruddy turnstones and laughing gulls (Table 9.2). For knots and 

turnstones, however, the time devoted to foraging when gulls were present was significantly less 

than when a nearest neighbor was any shorebird (Table 9.2). In addition, the mean number of 

pecks/30 seconds was significantly less when turnstones and sanderlings had gulls as nearest 

neighbors (Table 9.2). Besides actually feeding, foraging shorebirds engage in aggressive and 

vigilant behaviors. Red knots, turnstones, and to some extent dowitchers, spent more time being 

vigilant when their nearest neighbors were gulls rather than other shorebirds (Table 9.2). 

Similarly, knots, turnstones and semipalmated sandpipers engaged in more aggression when 

gulls were nearest neighbors (although they usually lost). 

Reduction of available horseshoe crab eggs or consolidation of spawning crabs onto fewer 

beaches could increase interference competition among egg foragers. Botton et al. (1994) noted 

that flocks of shorebirds appeared to be deterred from landing on beaches when large flocks of 

gulls were present. Maximum counts of gulls foraging along the New Jersey shoreline of 

Delaware Bay, however, may not have increased over the last decade, whereas breeding counts 

of laughing gulls (Larus atricilla) in Atlantic coast marshes may have increased (Table 9.1; L. 

Niles unpublished data). Details on survey methods are not provided. 

9.5. Red Knots Use of Food Other than Horseshoe Crab Eggs

Away from Delaware Bay, red knots primarily feed on molluscs and bivalves. Harrington and 

Winn (2001*) noted that prey of Georgia coast red knots were likely dwarf surf clams (Mulinia 

lateralis), and knots in South Carolina fed mainly on coquina clams (Donax variabilis). Food 

resources available to knots on the Virginia coast, where knot densities were highest, were blue 

mussels (Mytilus edulis) and Melitid amphipods (Truitt et al. 2001*). Preliminary information 

presented by Escudero and Niles (2001*) suggests that invertebrates in many Atlantic coast 

habitats are not dense enough to support the energetic needs of red knots. In samples of 7 New 

Jersey beaches, Botton et al. (1994) found that density of surface macroinvertebrates was seldom 

>200/m2

 and there were no significant differences in invertebrate density among beaches. Night 

feeding, use of alternative foods, and foraging patch residence time have been suggested as the 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 43 

behavioral modifications that demonstrate the inability of knots to meet their energetic 

requirements solely through horseshoe crab egg consumption (Sitters 2001*). Preliminary 

evidence suggests these behaviors are being used by knots, but lack of a historical perspective 

questions their significance. More detailed studies of prey quality (i.e. energy density) and 

quantity in the Delaware Bay region are needed to assess the significance of alternative prey, 

including assessment of temporal and spatial variation in prey abundance. 

González et al. (1996) studied the foraging ecology of red knots feeding on restingas at San 

Antonio Oeste, Argentina. Behavior of birds was recorded and fecal samples were collected, 

weighed, and analyzed to determine sizes and biomass of mussels (Brachidontes rodriguezi) 

ingested by knots. Mussel density and biomass were measured for 3 areas where feces were 

collected. Ash and ash-free dry mass were determined from samples to predict biomass of 

equivalent of droppings. Ivlev’s electivity index was used to determine if knots were selecting 

certain size classes. Defecation rates (droppings/bird-minute) were determined for a small area 

of a restinga. Numbers of knots fluctuated between 0 and 12,000 individuals in the area, and 

flocks tended to spend about 6–8 days at the stopover. Knots made repeated jabs to capture 

appropriately sized mussels and handling times were short (1–2 seconds). Mussel density ranged 

from 1,800 to 6,000 individuals (per m2

) which included 60–80% of sizes appropriate for 

ingestion by knots (5–20 mm, mean = 10.3 mm). Mussel biomass followed patterns of mussel 

density. Knot droppings exclusively contained mussels. Mean defecation rate of knots was 0.42 

droppings/bird-minute. This translated into an intake rate of 0.433 mg ash-free dry mass/second. 

Brachidontes mussels are rather slender and therefore ingestable by knots. Breaking forces of 

larger Brachidontes were less than similar-sized Mytilus. Optimistic projections suggest that 

knots may gain 5 g/day feeding on mussels. This refueling rate would allow fat accumulation to 

reach the next stopover in Brazil. Sitters et al. (2001) studied nocturnal distributions and 

foraging in radio-tagged red knots at a migratory stopover site near San Antonio Oeste, 

Argentina, during northward migration in and March and April 1998, and found that knots fed in 

habitats at night that differed from diurnal feeding sites. Previously González et al. (1996) 

reported that red knots cannot meet their daily requirements solely by feeding during the day. 

Brayton and Schneider (2000) found that the magnitude of shorebird use of beaches on the 

Peninsula Valdez, Argentina, did not correspond with prey density. Tidal exposure time was the 

best predictor of shorebird use. Gizzard and fecal analysis of red knots conducted at Punta Rasa, 

Argentina, in 1995 and 2000 (Alemany et al. 2001*) indicated that mudsnails (Heleobia 

australis), in the range of 1–3.5 mm in length, were the main prey taken. 

10.0 ENERGETIC REQUIREMENTS OF MIGRANT SHOREBIRDS

10.1. An Energetics Framework for Migrant Shorebirds

An energy based conceptual framework presented by Piersma (1996), was an effort to integrate 

research on energy intake and energy expenditure of birds. A shorebird’s energy budget consists 

of energy intake on the one side and energy expenditures on the other. Higher energy 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 44 

expenditures require higher energy intake. The energy expenditures consist of: 1) the Basal 

Metabolic Rate (BMR)—the energy consumed by a bird at rest, 2) the cost of 

thermoregulation—the energy required to maintain body temperature in lower temperatures, 

which will be higher with decreasing ambient temperature, 3) the cost of activity, and 4) the heat 

increment of feeding—the energy used in the digestive and assimilation process. The energy 

intake depends on the food and rate at which food can be consumed. For a specific diet item, 

functional response curves can describe the relationship between food abundance and food intake 

rates. For a diet consisting mainly of one food item (e.g., red knots foraging solely on Macoma 

balthica in the Dutch Wadden Sea), it is relatively easy to estimate the required intake rates and 

prey biomass needed to counterbalance the energy demands. However, these relationships 

become more complicated when a variety of prey items are consumed. The balance of the intake 

versus output is not constant throughout the year but differs depending on the season. For 

example, the balance is positive (energy stored) during preparation for migration, whereas the 

balance is strongly negative for a few days during long-distance flights (energy consumed with 

no intake). 

10.2. Energetics of Sanderlings Migrating to Four Latitudes

Castro et al. (1992) studied sanderlings that spend the winter at 4 different latitudes to quantify 

the energetic costs incurred by wintering at different latitudes. The study included measurements 

of daily energy expenditure, fat levels, and time budgets of sanderlings in New Jersey, Texas, 

Panama, and Peru. Daily energy expenditure was measured by injecting doubly labeled water 

into captured birds, releasing them in the wild, and finally calculating energy used from blood 

samples from these birds 24 hours later. No information is provided on the effects of handling. 

The collected birds were then analyzed to determine body composition and fat levels. Finally, 

time budgets were calculated by observing the activities of flocks of birds at all 4 locations, but 

behavior of the group may not necessarily be representative of the sampled individuals. Thermal 

environment explained 70% of the variance in sanderlings daily energy expenditure, with energy 

cost being twice as high in New Jersey as in Panama, and somewhere in between in Texas and 

Peru. Similarly, body mass and fat reserves of sanderlings were inversely correlated with air 

temperatures across sites. Sanderlings at all locations spent most of their time feeding or 

roosting. Time budgets between sites, with the exception of Texas, were similar and suggests 

that shorebirds manage to fulfill their living costs despite the high daily energy cost of the cold 

New Jersey winter. 

10.3. Predicting Flight Ranges

Castro and Myers (1988) developed equations to determine the cost of flight of shorebirds that 

were based on body mass and morphometric variables related to flight. These equations were 

statistically derived by regression of measured energy costs of flight, for a variety of species of 

birds, against body mass, wing length, wing span, and wing area. The model with the best fit 

included only 2 parameters—body mass and wing length. Compared to the models developed by 

Raveling and Lefebvre (1967) and Kendeigh (1977), the equations of Castro and Myers (1988) 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 45 

predict increasing costs of flight with increasing body mass. This discrepancy occurred because 

the other 2 models used allometric equations to predict cost flight as a simple function of body 

mass without taking aerodynamic design into consideration. Based on these equations, and 

allowing for loss in body mass during flight, Castro and Myers (1989) estimated the flight ranges 

of 6 species of shorebirds. The model can be expressed in the following equation: 

R = 26.88*S*L1.614*(M1

-0.464 - M2-0.464), where R = flight range (km), M1 = body mass at end of 

flight (g), M2 = body mass at the start (g), S = flight speed (km/h) and L = wing length (cm). 

Flight range estimates were determined based on the assumption of a 75 km/hour flight speed. 

Castro and Myers (1989) predict that although larger shorebirds can store more fat reserves, the 

flight distance is similar for large and small shorebird species. Using the Castro and Myers 

(1989) model, red knots would have depart Delaware Bay at a weight of 197 g to fly 2,400 km to 

arctic Canada and have 5 days worth of energy stores upon arrival. Mizrahi (1999) found that 

some Delaware Bay semipalmated sandpipers did not have enough fat reserves to reach breeding 

areas in James Bay and Labrador, Canada, and others were predicted to arrive with few (<1.0 g) 

reserves. Semipalmated sandpipers were very selective about wind conditions during departure, a 

behavior used to maximize flight energy efficiency. 

10.4. Fat-loading in islandica Red Knots

According to flight mechanics theory, flight costs increase with increasing body mass, and 

migrants should therefore avoid carrying large fat reserves. However, if migrants are under time 

constraints, such as the need to reach the breeding grounds as early as possible, they may need to 

carry heavier fat loads than those predicted based on energetic costs. Gudmundsson et al. (1991) 

present a theoretical framework to predict whether the birds are adapted to minimize energy or 

time spent on migration. During spring migration, when the birds are moving north, they are 

moving from staging sites with better and more predictable resources, which allow for fast fat 

deposition, to areas that are lesser quality feeding habitats. Under this scenario it is preferable to 

overload on fat reserves at sites that are richer in prey and by-pass the poorer ones. The authors 

present specific information for knots, turnstones and sanderlings captured in Iceland during 

northbound migration. At this site: knots depart at an mean body mass of 205.1 " 1.9 (SE) g (n

= 30; corresponding to 53.1% fat load), sanderlings depart at 82.6 " 1.2 (SE) g (n = 36; a 53% fat 

load), and ruddy turnstones depart at 161.6 " 2.4 (SE) g (n = 47 a 53.9% fat load). Based on 

these fat energy stores, flight ranges were estimated, and most shorebirds had greater fat loads 

than those required to complete their migration. These overloads may represent a time 

minimization strategy or a risk insurance against unfavorable conditions in other staging areas or 

the breeding grounds. Kvist et al. (2001), however, found that flight is not as metabolic 

expensive as originally thought (see next section). 

10.5. Effects of Weight on Metabolic Power Needed for Flight 

Kvist et al. (2001) experimentally investigated whether the predicted mechanical output required 

by increasing weight is reflected in increases in the metabolic energy input of birds in flight. 

They measured metabolic power input of 4 red knots during 28 flights in a wind tunnel using 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 46 

doubly labeled water. Metabolic power input during flight was calculated from CO2 production 

after correcting for energy that would be spent if the bird was not flying (1.5*basal metabolic 

rate). The metabolic power input increased allometrically with increasing body weight, with an 

exponent of 0.35. The flight muscle efficiency estimated from the measured power input and the 

predicted mechanical output also increased with increasing fuel load. This research indicates 

that red knots may maintain flight muscles at optimal size to decrease the energy requirements of 

migration. Therefore, the cost of carrying an additional unit of fuel may be lower than assumed 

in current models of bird migration. Muscle efficiency changes for migration may be 

incompatible with muscles structure changes needed for short transient flights, such as those 

needed to avoid predation. These results indicate a dynamic body mass model is needed to 

predict flight energy needs. 

10.6. Flight Energy Needs of rufa Red Knots Staging in Delaware Bay

 

Baker et al. (2003) determined if energetic stress during refueling was negatively affecting adult 

red knots in Delaware Bay. They assumed a 180 g average mass over the duration of a minimal 

flight of 2,400 km to Southampton Island and that energy can be predicted as log10 power (W) = 

0.39 + 0.35 log10 body mass (g), which is based on wind tunnel experiments of Kvist et al. 

(2001). Solving this equation yields a flight cost of 15W which translates into 54 kJ/hour. If the 

energy density of fat is 40 kJ/g, migrating birds will consume 1.35 g fat/hour. At a flight speed 

of 70 km/hour (Piersma et al. 1997), a flight of 2,400 km would require 47 g of fat. Maintenance 

on arrival would require 6.5 g/day (Piersma 2000). Based on lean mass of 130 g, departure 

weights of 180 g are minimal to cover migration to the arctic. 

10.7. Assimilation Efficiency of Sanderlings Consuming Horseshoe Crab Eggs

Castro et al (1989) experimented with captive sanderlings to determine the assimilation 

efficiency of captive birds fed a horseshoe crab egg diet. Eight sanderlings were captured in 

Delaware Bay in early May. These birds were kept in individual cages with a wire mesh floor 

and fed ad libitum an exclusive diet of horseshoe crab eggs. Horseshoe crab eggs for the feeding 

experiments were collected in the field, washed to remove debris and sand, and kept frozen. 

Mealworms were obtained commercially. Three experimental feeding trials were conducted 

during which the birds were fed horseshoe crab eggs, and 1 feeding trial during which the birds 

were fed mealworms. During those experiments the food consumed and excreta were collected 

and weighed. Collected samples were dried and analyzed to determine lipid, nitrogen, carbon, 

and energy content. On average, each sanderling ingested 30.9 g of eggs or 8,300 eggs/day. The 

eggs passed through the gastrointestinal tract in 63 minutes. The birds did not gain any weight 

during the 4 weeks of the experiment and their metabolic efficiencies were exceedingly low 

(39%). When the birds were switched to a diet of mealworms, the assimilation efficiency 

improved significantly (75%) and became more typical of the assimilation efficiency of birds 

eating foods of animal origin. While on the mealworm diet, the birds gained weight. However, 

large numbers of horseshoe crab eggs passed through the sanderlings’ digestive tract undigested. 

Metabolic efficiency corrected for unbroken eggs that are not assimilated was actually 69%, 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 47 

much closer to what would normally be expected. The sanderlings also consumed significantly 

higher amounts of food, as measured by dry mass influx, on the crab egg diet compared to the 

mealworm diet. Based on these results the authors suggest that the birds are taking advantage of 

the sheer abundance of eggs to maximize the rate of metabolizable energy intake. One of the 

issues raised in this research was the fact that a high proportion of eggs (71.9%) passed thought 

the digestive tract of sanderlings undigested. However, the eggs that the birds were fed had been 

washed, eliminating the presence of sand that grinds the egg membranes and enables fuller 

digestion of hard items. In actual field conditions, one might expect that the assimilation 

efficiency will be higher than 39% and might approach the 69% estimate of metabolic efficiency 

corrected for unbroken eggs. Both Tsipoura and Burger (1999) and Piersma (2000) found sand 

and gravel in the guts of red knots, which suggests assimilation efficiency could be as high as 

70%. 

10.8. Energy budget of Delaware Bay Shorebirds

Castro and Myers (1993) calculated the total energy consumption of shorebirds during spring 

stopover in Delaware Bay by estimating total energy requirements and correcting for 

assimilation efficiency of ingested food. To determine energy expenditure, basal metabolic rates 

(BMRs) were calculated based on the equations for shorebirds of Kersten and Piersma (1987). 

Daily energy expenditure was assumed to be 2.5*BMR based on doubly labeled water 

measurements on sanderlings (Castro and Myers 1988). Total energy expenditure was obtained 

by multiplying the daily energy expenditure by 21, assuming that the mean number of days 

shorebirds stay in Delaware Bay is about 3 weeks. Energy stored as fat was calculated assuming 

that shorebirds depart Delaware Bay at body fat levels of 40%. The populations of 6 species of 

shorebirds (ruddy turnstones, red knots, sanderlings, semipalmated sandpipers, dunlin, and 

dowitchers) using Delaware Bay during spring migration were included in this calculation. The 

authors estimated that total energy requirement for all species using Delaware Bay is 2,133 x 106

kJ. Total energy consumption for all species, assuming an assimilation efficiency of 38.6% [(the 

assimilation efficiency measured by Castro et al. (1989) for sanderlings feeding on horseshoe 

crabs; see below], is 5,526 x 106

 kJ. This is equivalent to 539 metric tons of horseshoe crab 

eggs. 

10.9. Horseshoe Crab Egg Requirement of Delaware Bay Shorebirds

If calculations by Castro and Myers (1993) are updated with information gathered since their 

publication [fat gains adjusted from the uniform 40% to 45% for red knots, 50% for ruddy 

turnstones, and 70% for sanderling (see sections in 9.0); assimilation efficiency is increased to 

70% (see section 10.7); and mean length of stay is reduced to 17 days (see section 7.2)], then 

total energy consumption by the 6 main species of shorebirds that use Delaware Bay beaches 

(ruddy turnstones, red knots, sanderlings, semipalmated sandpipers, dunlin, and dowitchers) 

would be 303 metric tons of horseshoe crab eggs (see Table 10.1). This does not account for any 

consumption by other shorebird species or other egg predators. Using Castro et al.’s (1989) 

energetic analysis, Botton et. al. (1994) suggested that egg densities were sufficient to support 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 48 

the entire Delaware Bay shorebird population (44,000 eggs/m2), and that beaches had the ability 

to support the numbers of shorebirds observed there. However, they assumed that all 160 km of 

Delaware Bay’s shoreline would provide foraging habitat for shorebirds and egg densities 

applied to a 20.8 m width of beach. Information on distribution of shorebirds and horseshoe 

crabs indicates that beaches of the upper bay are generally not used. If a minimum of 303 metric 

tons of eggs were required and suitable shoreline was reduced by a third to 120 km, a mid-beach 

surface density of 32,688 eggs/m2

 (20.8-m beach width) to 67,991 eggs/m2 (10-m beach width) 

would be needed to support the spring flight of shorebirds (423,000 birds). If the average daily 

consumption rate of eggs is 18,000 per day, the egg requirement is: 423,000 total shorebirds in 

Delaware Bay*14-day stay in the bay (the period of maximum egg consumption)*18,000 eggs 

consumed per day = 1.07 x1011 eggs (42,707 eggs/m2

, 20.8-m width). If red knots consumed 

18,000 eggs/day (see section 9.2), for 17 days, they would meet the energetic requirements of 

daily maintenance and adding an average of 5.23 g/day of fat during their stay in Delaware Bay 

(see Piersma 2000). Total red knot egg requirement would be 1.54*1010 eggs, which is within 

the same magnitude as the estimate Castro and Myers (1993) generated (1.75*1010 eggs), and 

suggests that the egg requirement derived above (1.07 x1011 eggs) could be realistic. 

Clearly, reliable data on egg availability is one of the most important information needs in 

Delaware Bay with regards to the status of shorebirds. No beaches surveyed 25–26 May 1999 in 

either New Jersey or Delaware had shallow sediment (0–5 cm) densities that were >33,000 

eggs/m2 and only 4 of 16 beaches had densities >10,000 eggs/m2 (see Table 8.1). Total sediment 

(0–20 cm) densities, however, were >33,000 eggs/m2 on 11 of 16 beaches surveyed. On 25 May 

2001, 2 of 7 beaches in Delaware had shallow sediment densities of >33,000 eggs/m2

 and 5 of 7 

beaches ha densities of >10,000 eggs/m2 (see Table 8.2). Sediment cores were collected during 

peaks of crab spawning in both years. More information on the temporal and spatial distribution 

of surface eggs is needed to determine if enough eggs are available to meet the energetic needs 

of foraging shorebirds. The wide variability in existing data on surface egg availability and the 

uncertainties surrounding beach dynamics and egg movement precludes drawing firm 

conclusions about whether or not shorebirds can satisfy their seasonal energetic requirements 

from horseshoe crab eggs. 

11.0. SHOREBIRD WEIGHTS AND WEIGHT GAIN

11.1. General Capture Methods

For studies of weight gain and survival, shorebirds are captured by either mist, cannon, or woosh 

nets during May and, occasionally, early June. Captured birds are placed in opaque holding 

cages (to reduce stress) where they await processing. Red knots lost about 3 g/hour during 

repeated measurements of held birds (Gillings 2002*). All birds are banded (ringed) with a 

metal band, and some receive a complement of color bands and flags. Birds are weighed, either 

by electronic balance or Pesola spring scale (mainly 1997), and some are measured for wing 

length, culmen length, fat score, and other characters. Plumage (% breeding), molt, and age are 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 49 

sometimes recorded. All birds are usually processed within 4 hour of capture. No random 

selection of capture sites is used or is there any systematic attempt to distribute catches sites 

along a north-south beach gradient. No information exists on how individual capture probability 

changes within season or across seasons. Catches vary in their composition relative to behavior, 

roosting or feeding, of captured birds. In Delaware Bay, 95 catches were made between 1997 

and 2002, and 52 catches yielded $50 red knots. From these catches, 9,692 red knots, 7,755 

sanderlings, and 10,106 ruddy turnstones were weighed. Samples varied in both time and space, 

which could lead to interpretation problems with the data. Most of the catches (73%) from 1997 

to 2002 were made on 2 beaches in Delaware (Mispillion Harbor and Slaughter Beach) and 2 

beaches in New Jersey (Cook’s and Reed’s Beaches; Table 11.1). Among years, the contribution 

of these sites to the overall capture varied between 36 and 100%, and the total number captured 

ranged from 893 to 2,431 knots (Table 11.1–2). Temporal distribution of catches also varies 

among years (Table 11.2), and netting did not begin until 22 May in 1997. 

11.2. Organ Atrophy and Weight Change during Migration

Changes in body mass and physiology during migration are not simply the result of changes in 

fat reserves. Muscle tissue and organs also undergo considerable fluctuations in mass 

(Lindström and Piersma 1993). To elucidate the changes in organ size during migratory 

stopover, Piersma (2000) randomly collected 6 Delaware Bay red knots on 4 dates in May 1998. 

Baker et al. (2003) compared birds captured on 28 May 1998 (6 females) to knots captured on 29 

May 1999 (2 males, 6 females) and on 25 May 2000 (1 male, 6 females). Previous work 

demonstrated no body size differences between males and females (Piersma et al. 1999). 

Carcasses were frozen and at a later date, body composition and morphological measures were 

made. Tissues were excised, dried, weighed, and fat-free mass was determined. Between 6 and 

14 May 1998, knots gained weight at 1.165 g/day, when virtually no fat was added. During the 

next 9 days, weight was gained at a rate of 6.391 g/day, and fat was added at 4.157 g/day. In the 

last 5 days, weight increased at 5.577 g/day and fat accumulated at 4.47 g/day. Most muscles 

slowly increased weight over the first 8 days and increased rapidly over the next 9 days. During 

the period of rapid weight gain, pectoral muscles increased by 50%, the heart increased by 40%, 

and leg muscles increased by 45%. The heart decreased slightly during the last 5 days before 

departure. Organs (Stomach, intestine, kidneys, liver) also increased dramatically (>50%) and 

stabilized during the last 5 days before departure. The lungs and spleen did not change mass 

during the period, but the salt glands mass increased steadily. Stomach contents indicated 

consumption of small stones, which would aid digestion of horseshoe crab eggs. Gradual 

changes in organs suggests that there was not a large pulse of recent arrivals in late May. These 

results were similar to studies of islandica knots at an Iceland spring staging site except that 

exercise organs increased in weight during the mid-period of migration (rather than at the end as 

in Iceland) and heart size declined prior to departure (Piersma et al. 1999). The vast changes in 

muscles and organs illustrate the importance of a high quality stopover, beyond fat deposition, 

for meeting energetic demands of migrating red knots. Information on other species in Delaware 

Bay is not currently available. Comparisons among years showed no significant differences in 

body size, body mass, total fat mass, or most organs and muscles (Baker et al. 2003). The only 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 50 

significant differences (P < 0.02) were that fat-free mass of pectoral muscles and the intestine 

was lower in 1999 (compared to 1998 and 2000) and that liver size was reduced in 1999 and 

2000 (compared to 1998). Reductions in these muscles and organs could compromise short- and 

long-term health of knots. In Delaware Bay, lean semipalmated sandpipers exhibited modulation 

of circulating corticosterone levels when exposed to stress (Mizrahi et al. 2000). Chronic levels 

of corticosterone can have a catabolic effect on striated muscle tissue, and this modulation may 

protect flight muscle structure during long-distance flights. 

11.3. Red Knot Weights through the Annual Cycle

As is characteristic of most migratory shorebirds, weights of red knots vary substantially 

throughout life history stages (Harrington 2001). Mass of red knots wintering in Tierra del 

Fuego ranges from about 120 to 135 g (Baker et al. 1998). Knots visiting one of the first known 

stopover sites during northward migration, Peninsula Valdez, Argentina, did not increase mass 

between 11 and 20 April. In Rio Negro Province, Argentina, Gonzáles et al. (1996) showed that 

knots during March were consuming mussels (Brachidontes spp.) at a rate that would enable a 

mean mass increase of <1 g/day. During early April, knots with partial or complete alternate 

plumage at Punta Rasa, in Buenos Aires Province, Argentina, had a mean mass of 139 g (138.9 +

16.9, n = 30) that was significantly heavier than basic-plumaged individuals (mean = 110.0 + 7.9 

g, n = 7). Body mass of adult and juvenile knots (n = 678) caught in Argentina during February 

and March 1997 was 120 g, and few birds weighed >140 g (Baker et al. 1998). During early 

May 1984, mean mass in southern Brazil was 202.2 g, the heaviest ever recorded for a sample of

rufa red knots. Basic-plumaged birds weighed significantly less than alternate-plumaged birds 

(155.0 g; Harrington et al. 1986). Nascimento (2001*) found that average weight of knots in 

May at Lagoa do Peixe was 192 g (n = 309, SD = 27). Knots generally gained weight from early 

to late April at Lagoa do Peixe (Baker et al. 1998). Further north on the Maranhão coast, the 

mean weight of knots captured in May was 153.6 g (range = 115–210 g, SD = 29.7), which 

suggests individuals may need to either gain weight or remain there for the boreal summer 

(Nascimento 2001). In the São Luís, Brazil, area, flocks were a mix of basic-plumaged, lightweight (assumed) sub-adults (mean = 140.1 g, SD = 10.1, n = 18) and heavier, alternativeplumaged adults (observed birds; Wilson et al. 1998). At Delaware Bay in the U. S., there was 

little change in mass before the third week of May (e.g., mean = 153.1 + 20.8, n = 129 on 19 

May), but a rapid increase during the last 10 days of the month (e.g., mean = 175.9 + 17.5 g, n = 

265 on 24 May; Harrington 2002). Knot weight needed for a successful flight to the arctic is 

thought to be at least 180 g (Piersma 2000). Threshold weights are suggested as 150 g for ruddy 

turnstones and 80 g for sanderlings (Gudmonsson et al. 1991). The mean weight of red knots 

measured 10 days after arrival on Southampton Island breeding grounds was 131.9 g (n = 18 

knots captured at nests). Four of the 18 knots weighed were below the lean mass value (120 g; 

Niles et al. 2001*). 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 51 

11.4. Red Knot Weight Gains in Delaware Bay

 11.4.1. Analytical approaches

Robinson et al. (2003*) used complementary analyses of mean weights of captured birds and of 

birds which were captured more than once during a season to determine patterns of weight gain. 

Although weight was correlated to body size, no systematic patterns of differential sizes in 

catches on different dates were evident. Wing lengths were not available for all samples, and 

weights were therefore generally not corrected for body size. Individual red knot cohorts (which 

were groups of birds characterized by different arrival dates) were identified with techniques for 

decomposing multiple Gaussian curves (with the FAO-ICLARM Fish Stock Assessment Tools 

package). The general notion is that weights are normally distributed after the arrival of a single 

flock and become multi-modal as other groups of birds arrive. This approach accounts for yearly 

differences in timing of arrival and departure. If samples are large, analysis of same-year 

individually re-captured birds is the ideal way to determine weight changes. Because capture 

effects can depress weight change over a short period of time, a minimum recapture period of 7 

days was used. 

Niles et al. (2003*) estimated arrival and departure mass by taking the mean mass of the lowestand highest-mass catches at the beginning and end of the season. The earliest catch was always 

used to determine arrival mass (generally >30 birds), but the mean departure mass may not have 

always been the latest catch. Multiple regression models were used to examine the influence of 

year, day, body size (bill, head, and flattened wing length), holding time, and time of capture on 

bird mass. Weight data were log10-transformed to meet assumptions of variance homogeneity. 

Because catch effort at the beginning and end of the season varied the most among years, 

analyses were restricted to 14–28 May. Daily rate of mass gain was derived from the regression 

coefficient of “day” in the regression model. Mass change was not computed for individual 

birds, but was considered a crude rate of mass gain of all birds across the season. Body size 

variables were only used in models of mass gain in knots, and time of capture was insignificant 

in models of sanderling mass gain. Regression results were compared to mean mass of catches 

at 3-day intervals for full and reduced (day only) for each year. Comparisons were also made to 

predicted rates of mass change from the full model. The proportion of the maximum number of 

shorebirds present on weekly aerial surveys was included as a covariate in regression analyses of 

crude rate of mass gain. Separate comparisons were made for New Jersey and Delaware sides of 

the bay. 

 11.4.2. Red knot arrival weights and weight gains

Mean arrival weight (" SE) was 114.9 " 1.6 g and was 12% below lean weight (Robinson et al. 

2003*). Mean arrival weight, across comparable years, ranged from 105.0 " 8.8 g (2000) to 

120.0 " 11.1 g (2001); the lowest arrival weight recorded was 85.9 g (30% below lean mass; 

Niles et al. 2003*). The highest weight recorded was 248.0 g (Niles et al. 2003*). Robinson et 

al. (2003*) suggested that arrival of knots appears to occur in 2 distinct periods: between 6 and 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 52 

10 May and between 20 and 24 May. Most of the red knots captured over the entire period were 

adults (Robinson et al. 2003*). Although weight was correlated to body size, no systematic 

patterns of differential sizes in catches on different dates were evident (Robinson et al. 2003*). 

However, significant (P < 0.0001), but slight, differences in wing lengths were found between 

sides of the bay, years, date within years. When size and date were included, sub-adult knot 

weights did not differ from adult weights (Robinson et al. 2003*). 

Robinson et al. (2003*) reported that weights of knots were relatively static until 11 May, after 

which average weight increased by 70.3 " 3.6 g. In general, weight gain followed a logistic 

growth pattern, and knots that initially arrived in the first period had gained weight when they 

were re-captured during the second period (Robinson et al. 2003*). Niles et al. (2003*) found 

that year, day, and a year-day interaction were significant predictors of crude rate of mass gain in 

knots (reduced model, R2 = 0.24), and that body size, holding time, and time of day were also 

significant (P < 0.02) predictors (full model, R2 = 0.29). Crude rate of mass gain was 5.22 g/day 

over all years, and a significant year*day interaction was caused by a decline from 8.5 g/day in 

1997 to 2.3 g/day in 2002. Netting operations in 1997, however, began late on 22 May. 

Significant year effects (P = 0.0375) on knot crude rate of mass gain remained after accounting 

for proportion of the peak aerial survey count, and the regression of year and residuals from the 

previous regression (crude rate of mass - newly arrived birds) was negative and significant (P

<0.0037). Weekly counts from aerial surveys are provided in Table 11.3. Mean mass of all 

species varied between states (P < 0.0001) and was generally higher in New Jersey. Although 

crude rate of mass gain declined in both states, the slope was somewhat steeper in Delaware, due 

to captures in 1997 (P = 0.044, year*state interaction; Niles et al. 2003*). Decreases in weight 

gain through the years were not monotonic (Table 11.4). 

Using the initial weight distribution and the mean of weight change, Robinson et al. (2003*) 

derived an expected distribution of weights for any given day (assuming growth is deterministic 

and constant among years). Following this method, there was no evidence that growth rates 

varied among years (Robinson et al. 2003*). Comparison of these predicted distributions with 

actual catch data indicates the presence of several cohorts in the catch. The relative number of 

knots weighing less than would be expected after 11 May has increased over time, and suggests 

more birds are arriving later (Robinson et al. 2003*). Knots arriving late can gain weight at a 

faster rate (#10 g/day; Robinson et al. 2003*). For 125 knots re-trapped within the same season, 

change in weight did not differ among years. Knots appear to be arriving later in Delaware Bay, 

and, in 2001 and 2002, second-arriving cohorts were 10 g lighter than earlier-arriving cohorts. 

Birds arriving by 16 May are predicted to reach target weight of 180 g by 28 May; those arriving 

after this date do not appear to do so (Robinson et al. 2003*). 

Differences in the results of these analyses have generated 2 possible hypotheses: 1) horseshoe 

crab eggs do not exist in sufficient amounts to enable knots to reach migration threshold weights, 

or 2) knots are arriving later in May and do not reach threshold weights. The late arrival 

hypothesis (2) is supported by the change in distribution of weights through the season among 

years, the lack of a year effect on weight gain in same-season re-trapped birds, and weight gains 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 53 

of knots are similar among different capture sites in Delaware Bay. Hypothesis 2 is countered by 

no shift in timing of knot counts on aerial surveys, no general change in the timing of color-band 

re-sightings, and that predicted distributions consistently overestimate actual numbers of highweight birds and under-estimate actual numbers of low-weight birds. Specific information on 

arrival of individually marked birds is needed to support or refute the arrival hypothesis, and 

much more information is needed on the condition of birds when they leave South America 

bound for Delaware Bay. 

 11.4.3. Red knot departure weights in Delaware Bay

Niles et al. (2003*) found that mean knot departure weights ranged from 26% to 51% above lean 

body mass. Baker et al. (2003) used logistic regression (0,1 if birds were in weight category by 

date) to determine the predicted percentage of knots in 4 mass categories ($160g, $180g, $190g, 

$200g) on 28 May from 1997 to 2002. The percentage of knots reaching 200 g on 28 May 

declined from 33.0% (1997) and 30.9% (1998) to 11.9% (2000) and 7.2% (2002). The same 

trend was detected in the most poorly-conditioned half of the population on 26 May (-20.5 g, ttest, P < 0.001), and a similar decreasing pattern existed for all weight categories (Baker et al. 

2003). For all birds combined, percentages of individuals reaching departure mass (180 g) 

decreased significantly for knots from 1997 to 2002 (34.5% to 7.1%, logistic regression, Wald P2

= 206, P < 0.0001; Niles et al. 2003*). Weight gains in knots banded in previous years, during 

the last 5 days before departure (23–28 May), were variable among years (1997 - 2001): 10.4 

g/day, 5.8 g/day, 2.6 g/day, 4.6 g/day, and 6.4 g/day. Despite a faster weight gain in late-arriving 

birds, Robinson et al. (2003*) found that only 42% of birds arriving on 20 May 2002 achieved 

target departure weight (180 g) by 28 May 2002 and only 84% of the more earlier arriving cohort 

reached target weight (vs. 95% in 1998). That fewer red knots are reaching migration threshold 

weights by the end of May in Delaware Bay is consistent among all analytical approaches. 

11.5. Weights and Weight Gain in Ruddy Turnstones and Sanderlings

Niles et al. (2003*) found that ruddy turnstone arrival mass varied between 94.6 " 8.6 and 98.6 "

15.5 g, which was 6.1–9.9% below lean body mass (105 g). Arrival mass of sanderlings (49.6 " 

4.6), however, was closer their lean body mass (52 g) than either red knots or turnstones. 

Virtually all turnstones and sanderlings captured (>98%) were adults (Robinson et al. 2003*). 

Ruddy turnstones and sanderlings followed a similar weight gain schedule as knots (Robinson et 

al. 2003*). Relative to their arrival weights, turnstones increase their weight by 55%, at a rate of 

7.2 " 1.1 g/day and sanderlings by 70% (4.5 " 1.3 g/day). Mean departure weight increases over 

lean body mass ranged from 46% to 52% for turnstones, and 48% to 80% for sanderlings 

(Robinson et al. 2003*). Year, day, and a year*day interaction, along with holding time and time 

of day, were significant predictors (P < 0.001) of crude rate of mass gain in turnstones (full 

model, R2

 = 0.42; Niles et al. 2003*). The crude rate of mass gain in ruddy turnstones only 

slightly declined over the period (0.5 g/day difference among years), and arriving birds did not 

significantly influence the crude rate of mass gain (Niles et al. 2003*). Analysis of individually 

re-trapped turnstones indicated a significant difference in weight gain among years (P2

 = 10.82, 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 54 

P = 0.029), but there was no consistent trend across years and differences between years were 

<10% (Robertson et al. 2003*). Proportions of ruddy turnstones reaching departure mass (150 g) 

declined slightly for turnstones between 1997 and 2002 (logistic regression, Wald P2

 = 206, P < 

0.025; Niles et al. 2003*). No trends were apparent in sanderlings for crude rate of mass gain, 

mass gain of re-trapped birds, or proportion of individuals reaching departure mass. Differences 

between states were minor for ruddy turnstones and absent for sanderlings. Because ruddy 

turnstones can dig for horseshoe crab eggs and sanderlings feed on a variety of invertebrates, 

they should be less sensitive than red knots to changes in surface egg density. 

11.6. Weights and Weight Gain in Semipalmated and Least Sandpipers

Mizrahi (2002*) captured and weighed semipalmated and least sandpipers in Delaware Bay, 

between 1996 and 2002, to determine daily rates of fat or mass gain, the energetic condition of 

sandpipers, and whether these indices have changed since 1996. Least sandpipers migrate earlier 

in May through Delaware Bay and are primarily found in marshes, whereas semipalmated 

sandpipers are more dependent on horseshoe crab eggs for feeding and migration phenology. 

Sandpipers were captured at Thompson’s Beach (1996, 1997, 2000, 2001, 2002) and Raybins 

Beach (1996, 2000, 2002). Between 1997 and 2001, $90,000 horseshoe crabs were annually 

harvested at Thompson’s Beach; harvest was minimal before 1996 and the beach was closed to 

harvest in 2002. However, harvest did occur at nearby areas. Thompson’s Beach is mainly used 

by species that forage on mudflats. Energetic condition of semipalmated sandpipers (fat mass) 

was estimated using a published regression model, and of least sandpipers by a published index 

that adjusted body mass for individual size. Linear regression was used to determine the 

relationship between date (starting 17 May for semipalmated and 8 May for least) and energetic 

condition; only days with > 6 captures were included in the analysis. Analyses were conducted 

in 2 spatial groups (Thompson’s Beach and Thompson’s/Raybins combined) and in 2 time 

periods (all days and maximum mass gain period). Visual examination of residuals was made to 

ensure linear, parametric model assumptions were met. Effects of year were tested using an 

analysis of covariance. Significance of among-year comparisons was calculated with the 

Bonferroni adjustment. 

Analysis of covariance showed highly significant year and date effects (P # 0.001) in 

semipalmated sandpipers for all days and for the period of maximum weight gains. Additionally, 

the interaction of date*year was highly significant (P # 0.0001), suggesting among year 

differences in daily fat mass gain. Fat mass gain in 1996 for combined Thompson’s/Raybins 

cohorts (0.93–1.18 g/day, depending on analysis) was significantly greater compared to other 

years (0.41–0.45 g/day, averaged across years), which generally showed no among-year 

differences. Similarly, mean cohort fat mass was significantly greater in 1996 (8.77–9.97 g, 

depending on analysis) compared to other years (6.84–7.04 g depending on analysis, averaged 

across years) which showed no among-year differences. However, data from Thompson Beach 

alone showed more variability among years. In 1996, fat mass gain rate was 1.14–1.18 g/day (all 

days analysis and maximum mass gain period). By 2000, fat mass gain rates had declined to 

0.18 g/day, and in 2002, the rate decreased to 0.08 g/day. No significant year effect or year-date 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 55 

interactions were found in least sandpipers, suggesting that rates of energy accumulation did not 

change significantly among years. Thus, semipalmated sandpipers showed a marked (.50%) 

and significant decrease in rates of energy accumulation from 1997–2002 relative to 1996, and, 

depending on year or analysis category, annual mean fat mass declined 8–41% compared to 

1996. However, no significant change in rates of energy accumulation in least sandpipers was 

evident between 1996 and 2002, and mean energy condition varied only 4–10% among years. 

Differences between these congenerics may be attributable to differences in migration phenology 

and foraging ecology during spring stopovers in Delaware Bay. 

12.0. RED KNOT SURVIVAL AND PRODUCTIVITY

12.1. Re-sighting Rates of Knots Banded in Florida and Argentina

Harrington et al. (1988) compared re-sighting rates of red knots wintering in Patagonia and 

Florida. Between 1980 and 1986, they banded 3,316 knots in Massachusetts, New Jersey, 

Florida, and Argentina. Of 309,013 knots scanned over a 5-year period, 1,730 flagged birds 

were re-sighted. After each site-year visit, re-sighting rate for each band class was calculated as: 

[(number re-sighted)number banded))number scanned]. The log2 of re-sighting rate was 

regressed against time since banding, and site-specific regression slopes were compared to 

determine location effect. Regression slopes ($) were used to determine annual re-sighting rate 

(sensu Caughley 1977) as: ps = e12$. Relative to Florida (3.04%, n = 263 marked), a significantly 

higher percentage (P2 = 16.7, P < 0.01) of red knots banded in Argentina (13.8%, n = 181 

marked) were re-sighting in New Jersey or Massachusetts. No birds banded in either Argentina 

or Florida were found at the opposite site. Although these wintering populations appear discrete, 

wing and bill lengths of birds captured at each site did not differ (ANOVA, P > 0.05). Slopes of 

regression of log2 re-sighting rate vs. time since banding were significantly different (ANOVA, 

P = 0.014). The difference was due to Florida; slopes for Massachusetts and New Jersey did not 

differ (P = 0.865). Re-sighting rate of birds wintering in Florida (ps = 0.758, $ = -0.023, R2

 = 

0.692, P = 0.020) was twice that of birds wintering in Argentina (New Jersey: ps = 0.340, $ = -

0.089, R2

 = 0.691, P = 0.011; Massachusetts: ps = 0.358, $ = -0.0855, R2 = 0.810, P = 0.0001). 

Because of similar re-sighting rates between New Jersey and Massachusetts, evidence suggests 

that knots are site faithful during migration. Age structure should not influence differences in 

Florida birds after the first re-sighting year. Low re-sighting rates could be due to some band 

loss in the population. 

12.2. Survival Rate

To determine effects of reduced departure mass on return rate, Baker at al. (2003) analyzed 

return rates of adults relative to capture mass and mark-recapture data from catches. Red knots 

known to survive $1 year after capture had a heavier initial capture weight than birds that were 

not re-sighted (ANOVA, F = 13.8, P < 0.001), which suggests that knots arriving earlier in May 

should have more time to gain weight and enhance survival. However, known survivors 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 56 

captured during the peak of migration 15–30 May (n = 383, mass of birds set on 23 May) 

showed a decline in predicted departure mass on 28 May in recent years. Observed mass on 23 

May was calculated by fitting a log-link General Linearized Model of known survivor weights 

with date and year as covariates. Median dates of capture of known survivors did not change 

among years (Kruskal-Wallis, H = 4.163, P = 0.329). Mark-recapture analysis was restricted to 

re-sighting of knots flagged in either Tierra del Fuego or southern Brazil. The program U-care 

confirmed that Cormack-Jolly-Seber assumptions estimators were met, and program MARK 

(2.1) was used to estimate survival rates (for 3-year periods). Although annual survival tended to 

decline from 86.7% (1994/95–1997/98) to 53.9% (1998/99–2000/01), 95% confidence limits 

(determined from profile likelihood; 0.54–1.00, 0.45–0.633) overlapped among these periods. 

An estimate for 2001/02 was highly variable (0.49–1.00, 95% confidence limit; Baker et al. 

2003). During a population decline of islandica knots in Britain, annual adult survival was only 

76%, whereas annual adult survival was 80% when the population was stable (Boyd and Piersma 

2001). Confidence limits during 1998/99–2000/01 were well below the mean adult survival 

Britain-wintering knots. Greater effort to re-sight and recapture marked birds would improve the 

ability to estimate and interpret survival rate data. Inscribed color flags have been suggested as a 

way to increase accuracy and ease of identifying individuals scanned from flocks (Atkinson et al. 

2003). 

12.3. Population Projections

Baker et al. (2003) constructed a matrix model to evaluate demographic effects of current vital 

rates. No information exists for juvenile survival of rufa red knots, but is about 25% of adult 

survival in islandica knots (Boyd and Piersma 2001). Similarly, no information exists on knot 

fecundity. If juvenile survival is 50% of adult survival in the best years (87.6%), and fecundity 

is uniformly distributed with a mean of 0.29 (maximum = 0.58, minimum = 0.0), then the Tierra 

del Fuego population is estimated to be stable at about 70,000 birds. If adult survival continues 

at the lower level (53.9%), the population is predicted to be extinct or nearly so by 2010. No 

probabilities of extinction at different adult survival rates, however, were provided in the 

analysis. Aerial counts made in Tierra del Fuego in 2003 were slightly higher than counts made 

in 2002 (R. I. G. Morrison, personal communication) and suggest that probability of extinction 

by 2010 is likely low. 

12.4. Juvenile Age Ratios 

Based on observations of wintering and early spring flocks of red knots, Baker et al. (2003) 

reported that the percentage of juveniles in captures made in Tierra del Fuego has gradually 

declined from 19% in 1995 (Rio Grande, n .500 knots) to 16% in 2000 (Rio Grande, n .500) to 

10% in 2001 (Rio Grande, n .500), 6% in 2002 (Bahía Lomas, n = 231), and 5% in 2003 (Bahía 

Lomas, n = 200). In 1995, the percentage of immature knots was much lower in catches 

northward of Tierra del Fuego in Rio Grande at Punta Rasa, Argentina (8%, n = 66), and Lagoa 

do Peixe, Brazil (4.6%, n = 394). The mean percentage of juvenile islandica knots wintering in 

Britain ranged from 29% in years of increasing numbers to 14% in stable years to 12% in years 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 57 

of decreasing numbers (Boyd and Piersma 2001). Recent estimates from Tierra del Fuego are 

well below even the mean of the worst years in Britain. For 21 years when >50 knots were 

captured at Ottenby, Sweden, the proportion of juveniles was 37.4% and ranged from 0 to 95%. 

The percentages of juveniles in catches of red knots in Australia, the southern migration terminus 

of C. c. rogersi, varied 3–14% (northwest) and 3–69% (southeast; Minton et al. 2002*). Neither 

site had sequential years at low levels. Successive years of poor recruitment would certainly 

contribute to population declines. 

13.0. LITERATURE CITED 

(* indicate unpublished reports, submitted manuscripts, or abstracts) 

Andres, B. A. 1999. Effects of persistent shoreline oil on breeding success and chick growth in 

black oystercatchers. Auk 116:640–650. 

*Alemany, D., E. Ieno, D. Blanco, and R. Bastida. 2001. Red knot diet and prey size selection 

during northward migration at Punta Rasa, Buenos Aires, Argentina. Wader Study 

Group Bulletin 95:17–18 (abstract). 

*Atkinson, P. W., N. A. Clark, and R. A. Robinson. 2003. Survival Rates and Body Condition 

of red Knots in Delaware Bay—Influence of Body Condition at Departure on Survival, 

Chapter 1. British Trust for Ornithology Research Report No. 308, Thetford, Norfolk, 

United Kingdom. 41 pp. 

*Atlantic States Marine Fisheries Commission. 1998a. Interstate fishery management plan for 

the horseshoe crab. Fishery Management Report No. 32, Washington, D. C. 50 pp. 

*Atlantic States Marine Fisheries Commission. 1998b. Terms of reference and advisory report 

for the horseshoe crab stock assessment peer review. Stock Assessment Report No. 98-

01, Washington, D. C. 13 pp. 

*Atlantic States Marine Fisheries Commission. 1998c. Horseshoe crab stock assessment report 

for peer review. Stock Assessment Report No. 98-01 (Supplement), Washington, D. C. 

43 pp. 

*Atlantic States Marine Fisheries Commission. 2000. Addendum I to the Fishery Management 

Plan for Horseshoe Crab. Fishery Management Report No. 32a, Washington, D. C. 9 pp. 

*Atlantic States Marine Fisheries Commission. 2001. Addendum II to the Fishery Management 

Plan for Horseshoe Crab. Fishery Management Report No. 32a, Washington, D. C. 5 pp. 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 58 

*Aubry, Y., and R. Cotter. 2001. Using trend information to develop the Quebec shorebird 

conservation plan. Canadian Wildlife Service Bird Trends 8:21–25. 

Baker, A. J., P. M. Gonzalez, L. J. Niles, T. Piersma, I. L. S. Nascimento, P. W. Atkinson, N. A. 

Clark, C. D. T. Minton, M. Peck, H. Sitters, and G. Aarts. 2003. Rapid population 

decline in red knots Calidris canutus rufa since 2000: fitness consequences of late arrival 

and decreased refueling rates in Delaware Bay. Science 299: in press. 

Baker, A. J., P. M. Gonzalez, T. Piersma, C. D. T. Minton, J. R. Wilson, H. Sitters, D. Graham, 

R. Jessop, P. Collins, P. de Goeji, M. K. Peck, R. Lini, L. Bala, G. Pagnoni, A. Vila, E. 

Bremer, R. Bastida, E. Ieno, D. Blanco, S. de Lima, I. Do Nascimento, S. S. Scherer, M. 

P. Schneider, A. Silva, and A. A. F. Rodrigues. 1998. Northbound migration of red 

knots Calidris canutus rufa in Argentina and Brazil: report on results obtained by an 

international expedition in March and April 1997. Wader Study Group Bulletin 88:64–

75. 

*Bart, J. R., S. Brown, R. I. G. Morrison, and B. A. Harrington. 2003. Population trends of 

North American shorebirds. Auk 119: submitted

*Below, T. H. 2001. Red knot monitoring in southwest Florida. Wader Study Bulletin 95: 11–

12 (abstract). 

Berkson, J., and C. N. Shuster, Jr. 1999. The horseshoe crab: the battle for a true multiple-use 

resource. Fisheries 24:6–10 

Blomqvist, S., N. Holmgren, S. Åkesson, A. Hedenström, and J. Pettersson. 2002. Indirect 

effects of lemming cycles on sandpiper dynamics: 50 years of counts from southern 

Sweden. Oecologia 133:146-158. 

Botton, M. L. 1984. Effects of laughing gull and shorebird predation on the intertidal fauna at 

Cape May, New Jersey. Estuarine, Coastal and Shelf Science 18:209–220. 

Botton, M. L. 1993. Predation by herring gulls and great black-backed gulls on horseshoe crabs. 

Wilson Bulletin 105:518–521. 

Botton, M. L. 2000. Toxicity of cadmium and mercury to horseshoe crab (Limulus polyphemus) 

embryos and larvae. Bulletin of Environmental Contaminants and Toxicology 64:137–

143. 

Botton, M. L., K. Johnson, and L. Helleby. 1998. Effects of copper and zinc on embryos and 

larvae of the horseshoe crab, Limulus polyphemus. Archives of Environmental 

Contamination and Toxicology 64:25–32. 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 59 

Botton, M.L., R.E. Loveland, and T.R. Jacobsen. 1988. Beach erosion and geochemical factors: 

influence on spawning success of horseshoe crabs (Limulus polyphemus) in Delaware 

Bay. Marine Biology 99:325–332. 

Botton, M. L., R. E. Loveland, and T. R. Jacobsen. 1994. Site selection by migratory shorebirds 

in Delaware Bay, and its relationship to beach characteristics and abundance of horseshoe 

crab (Limulus polyphemus) eggs. Auk 111:605–616. 

Botton, M. L., and J. W. Ropes. 1987. Populations of horseshoe crabs, Limulus polyphemus, on 

the northwestern Atlantic continental shelf. Fisheries Bulletin 85:805–812. 

Boyd, H. 1992. Arctic summer conditions and British knot numbers: an exploratory analysis. 

Wader Study Group Bulletin 64 (supplement):144–152. 

Boyd, H., and T. Piersma. 2001. Changing balance between survival and recruitment explains 

population trends in red knots Calidris canutus islandica wintering in Britain, 1969–1995. 

Ardea 89:301–317. 

Brayton, A. F., and D. C. Schneider. 2000. Shorebird abundance and invertebrate density 

during the boreal winter and spring at Peninsula Valdez, Argentina. Waterbirds 23:277–

282. 

*Brousseau, L .J., M. Sclafani, D. R. Smith and D. B. Carter. 2002. Acoustic and radio tracking 

of horseshoe crabs (Limulus polyphemus) to assess foreshore and subtidal habitat use in 

Delaware Bay. Annual Meeting of the American Fisheries Society, Baltimore, Maryland 

(poster). 

*Brown, S., C. Hickey, B. Harrington, and R. Gill (editors). 2001. The U. S. shorebird 

conservation plan, second edition. Manomet Center for Conservation Sciences. 

Manomet, Massachusetts. 60 pp. 

Buckel, J. A., and K. A. McKown. 2002. Competition between juvenile striped bass and 

bluefush: resource partitioning and growth rate. Marine Ecology Progress Series 

234:191–204 

Buhl-Mortensen, L., and S. Welin. 1998. The ethics of doing relevant science: the 

precautionary principle and the significance of non-significant results. Science and 

Engineering Ethics 4:401–412. 

Burger, J. 1981. The effect of human activity on birds at a coastal bay. Biological Conservation 

21:231–241. 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 60 

Burger, J. 1997. Heavy metals in the eggs and muscle of horseshoe crabs (Limulus polyphemus) 

from Delaware Bay. Environmental Monitoring and Assessment 46:279–287. 

Burger, J., D. Caldwell Hahn, and J. Chase. 1979. Aggressive interactions in mixed-species 

flocks of migrating shorebirds. Animal Behaviour 27:459–469. 

Burger, J., C. Dixon, T. Shukla, N. Tsipoura, and M. Gochfeld. 2002a. Metal Levels in 

Horseshoe Crabs (Limulus polyphemus) from Maine to Florida. Environmental Research 

90:227–236. 

Burger, J., C. Dixon, T. Shukla, N. Tsipoura, H. Jensen, M. Fitzgerald, R. Ramos and M. 

Gochfeld. 2002b. Metals in Horseshoe Crabs from Delaware Bay. Archives of 

Environmental Contaminants and Toxicology 44:36–42. 

Burger, J., and M. Gochfeld. 1991. Human activity influence and diurnal and nocturnal 

foraging of sanderlings (Calidris alba). Condor 93:259–265. 

*Burger J., C. Jeitner, and S. Carlucci. 2003. Foraging behavior of shorebirds and gulls at a 

migratory stopover in Delaware Bay. Unpublished report, Nelson Biology Laboratory, 

Rutgers University, Piscataway, New Jersey. 

Burger, J., L. Niles, and K. E. Clark. 1997. Importance of beach, mudflat, and marsh habitats to 

migrant shorebirds on Delaware Bay. Biological Conservation 79:283–292. 

Burger, J., S. Seyboldt, N. Morganstein, and K. Clark. 1993. Heavy metals and selenium in 

feathers of three shorebird species from Delaware Bay. Environmental Monitoring and 

Assessment 28:189–198. 

*Carter, D. 2002. Preliminary analysis of red knot and turnstone concentration areas in 

Delaware 1997–2000. Unpublished report, Delaware Coastal Management Programs, 

Dover, Delaware. 

*Carter, D. B., N. A. Clark, and J. D. Hewes (editors). 2002. Delaware Bay – 2000/2001 the 

Delaware shorebird monitoring team bi-annual report. Unpublished report, Delaware 

Coastal Management Programs, Dover, Delaware. 

*Carter, D., and R. R. Scarborough. 2002. Local wind direction and intensity as a major factor 

for habitat preference and utilization by red knot on Delaware Bay during spring 

migration. Unpublished report, Delaware Coastal Management Programs, Dover, 

Delaware. 

Castro, G., and J. P. Myers. 1988. A statistical method to estimate the cost of flight in birds. 

Journal Field Ornithology 59:369–38 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 61 

Castro, G., and J. P. Myers. 1989. Flight range estimates for shorebirds. Auk 106:474–476. 

Castro, G., J. P. Myers, and A. R. Place. 1989. Assimilation efficiency of sanderlings (Calidris 

alba) feeding on horseshoe crab (Limulus polyphemus) eggs. Physiological Zoology 

62:716–731. 

Castro, G., J. P. Myers, and R. E. Ricklefs. 1992. Ecology and energetics of sanderlings 

migrating to four latitudes. Ecology 73:833–844. 

Castro, G., and J. P. Myers. 1993. Shorebird predation on eggs of horseshoe crabs during spring 

stopover on Delaware Bay. Auk 110:927–930. 

Caughley, G. 1977. Analysis of vertebrate populations. John Wiley & Sons, New York, New 

York. 244 pp. 

Clark, K. E., L. J. Niles, and J. Burger. 1993. Abundance and distribution of migrant shorebirds 

in Delaware Bay. Condor 95:694–705. 

*Clark, K. E. and L. J. Niles (editors). 2000. Northern Atlantic regional shorebird plan, version 

1.0. Unpublished report, New Jersey Endangered and Nongame Species Program, 

Division of Wildlife, Trenton, New Jersey (available at <http://shorebirdplan.fws.gov>). 

Cooper, J. M. 1994. Least sandpiper (Calidris minutila). Pages 1–28 in A. Poole and F. Gill, 

editors. The birds of North America, No. 115. Academy of Natural Sciences, 

Philadelphia, and The American Ornithologists' Union, Washington D. C. 

Davidson, N. C., and P. I. Rothwell. 1993. Disturbance to waterfowl on estuaries: the 

conservation and coastal management implications of current knowledge. Wader Study 

Group Bulletin 68:97–105. 

*Escudero, G., and L. J. Niles. 2001. Are there alternative food resources for knots in Delaware 

Bay? Wader Study Group Bulletin 95:13 (abstract). 

*Eubanks, T. L., J. R. Stoll, and P. Kerlinger. 2000. The economic impact of tourism based on 

horseshoe crab-shorebird migration in New Jersey. Unpublished Report, Fermata, Inc., 

Austin, Texas. 91 pp. 

*Eyler S., and M. Millard. 2002. Spawning frequency and beach fidelity of horseshoe crabs in 

Delaware Bay. Annual Meeting of the American Fisheries Society, Baltimore, Maryland 

(poster). 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 62 

*Falkingham, J. C., R. Chagnon, and S. McCourt. 2001. Sea ice in the Canadian arctic in the 

21st century, chapter II:12. The state of the arctic cryosphere during the extreme warm 

summer of 1998: documenting cryospheric variability in the Canadian arctic. Final 

report, CCAF summer 1998 project team, Environment Canada (available at 

<http://www.socc.ca>). 

Figuerola, J. 1999. Effects of salinity on rates of infestation of waterbirds by haematozoa. 

Ecography 22: 681-685. 

Galbraith, H., R. Jones, R. Park, J. Clough, S. Herrod-Julius, B. Harrington, and G. Page. 2002. 

Global climate change and sea level rise: potential losses of intertidal habitat for 

shorebirds. Waterbirds 25: 173–183. 

Gill, J. A., K. Norris, and W. J. Sutherland. 2001. Why behavioural responses may not reflect 

the population consequences of human disturbance. Biological Conservation 97:265–268. 

Gill, R. E., Jr., P. Canevari, and E. H. Iversen. 1998. Eskimo curlew (Numenius borealis). 

Pages 1–28 in A. Poole and F. Gill, editors. The birds of North America, No. 347. 

Academy of Natural Sciences, Philadelphia, and The American Ornithologists' Union, 

Washington D. C. 

*Gillings, S. 2002. What is the rate of weight loss between capture and weighing for red knots 

processed in Delaware and New Jersey in May 1998, 1999, and 2000 and how do weights 

change through migration. Unpublished report, Delaware Coastal Management 

Programs, Dover, Delaware. 

*Galofre, J. 2002. Beach nourishment analysis of Delaware Bay beaches in Delaware state and 

applications to coastal management. Unpublished report, Delaware Department of 

Natural Resources and Environmental Control. Dover, Delaware. 

González, P. M., T. Piersma, and Y. Verkuil. 1996. Food, feeding, and refueling of red knots 

during northward migration at San Antonio Oeste, Rio Negro, Argentina. Journal of 

Field Ornithology 67:575–591. 

*González, P. M., D. Price, and G. Morrison. 2001. Migration of knots through Bahía de San 

Antonio, Río Negro, Argentina. Wader Study Group Bulletin 95:11 (abstract). 

Goss-Custard, J. D. and N. Verboven. 1993. Disturbance and feeding shorebirds on the Exe 

estuary. Wader Study Group Bulletin 68:59–66. 

Gratto-Trevor, C. L. 1992. Semipalmated sandpiper (Calidris pusilla). Pages 1–20 in A. Poole 

and F. Gill, editors. The birds of North America, No. 6. Academy of Natural Sciences, 

Philadelphia, and The American Ornithologists' Union, Washington D. C. 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 63 

Gretton, A. 1991. Conservation of the Slender-billed Curlew. International Council for Bird 

Preservation Monograph No. 6, Cambridge, England. 159 pp. 

Gudmundsson, G. A., Å. Lindström, and T. Alerstam. 1991. Optimal fat loads and longdistance flights by migrating knots (Calidris canutus), sanderlings (C. alba), and 

turnstones (Arenaria interpres). Ibis 133:140–152. 

*Haramis, G. M., M. A. Teece, and D. B. Carter. 2002. Use of stable isotopes to determine the 

relative importance of horseshoe crab eggs in the diet of long-distance migrant shorebirds 

in Delaware Bay. Unpublished report, Delaware Coastal Management Programs, Dover, 

Delaware. 

Harrington, B. A. 2001. Red knot (Calidris canutus). Pages 1–32 in A. Poole and F. Gill, 

editors. The birds of North America, No. 563. Academy of Natural Sciences, 

Philadelphia, and The American Ornithologists' Union, Washington D. C. 

*Harrington, B. A. 2002. Shorebird migration on Delaware Bay – Pondering the numbers. 

Unpublished report, Manomet Center for Conservation Sciences, Manomet, 

Massachusetts. 

Harrington, B. A., P. de T. Z. Antas, and F. Silva. 1986. Northward shorebird migration on the 

Atlantic coast of southern Brazil. Vida Silvestre Neotropical 1:45–54. 

*Harrington, B., and N. Drilling. 1996. Investigations of effects of disturbance to migratory 

shorebirds at migration stopover sites on the U. S. Atlantic coast. Unpublished report, 

Manomet Center for Conservation Sciences, Manomet, Massachusetts. 

Harrington, B. A., J. A. Hagan, and L. E. Leddy. 1988. Site fidelity and survival differences 

between two groups of New World red knots (Calidris canutus). Auk 88:439–445. 

Harrington, B. A., and R. I. G. Morrison. 1979. Semipalmated sandpiper migration in North 

America. Studies in Avian Biology 2:83-100. 

*Harrington, B. A., and B. Winn. 2001. Red knots of southeastern United States: A preliminary 

report of recent investigations into the insular qualities of the population. Wader Study 

Group Bulletin 95:12 (abstract). 

Helmers, D. L. 1992. Shorebird Management Manual. Western Hemisphere Shorebird Reserve 

Network, Manomet Center for Conservation Sciences, Manomet, Massachusetts. 58 pp. 

Hicklin, P. W. 1987. The migration of shorebirds in the Bay of Fundy. Wilson Bulletin 

99:540–570. 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 64 

Hitchcock, C. L., and C. Gratto-Trevor. 1997. Diagnosing a shorebird local population decline 

with a stage-structured population model. Ecology 78:522–534. 

Hockin, D., M. Ounsted, M. Gorman, D. Hill, V. Keller, and M. A. Barker. 1992. Examination 

of the effects of disturbance on birds with reference to its importance in ecological 

assessments. Journal of Environmental Management 36:253–286. 

Hollander M., and D. A. Wolfe. 1973. Non-parametric statistical methods. John Wiley & Sons, 

Inc. New York, New York. 503 pp. 

Howe, M. A., P. H. Geissler, and B. A. Harrington. 1989. Population trends of North American 

shorebirds based on the International Shorebird Survey. Biological Conservation 

49:185–199. 

Itow, T., T. Igarashi, R. E. Loveland, and M. L. Botton. 1998a. Heavy metals inhibit limb 

regeneration in horseshoe crab larvae. Archives of Environmental Contamination and 

Toxicology 35:457–463. 

Itow, T., R. E. Loveland, and M. L. Botton. 1998b. Developmental abnormalities in horseshoe 

crab embryos caused by exposure to heavy metals. Archives of Environmental 

Contamination and Toxicology 35:33–40. 

Jehl, J. R. Jr., J. Klima, and R. E. Harris. 2001. Short-billed dowitcher (Limnodromus griseus). 

Pages 1–28 in A. Poole and F. Gill, editors. The birds of North America, No. 564. 

Academy of Natural Sciences, Philadelphia, and The American Ornithologists' Union, 

Washington D. C. 

Kendeigh, S. C., V. R. Dolnick, and V. M. Gavrilov. 1977. Avian energetics. Pages 127–204 in

J. Pinowski and S. C. Kendeigh, editors. Granivorous birds in ecosystems. Cambridge 

University Press, New York, New York. 431 pp. 

Kersten, M., and T. Piersma. 1987. High levels of energy expenditure in shorebirds: metabolic 

adaptations to an energetically expensive way of life. Ardea 75:175–187 

Koolhaas, A., A. Dekinga, and T. Piersma. 1993. Disturbance of foraging Knots by aircraft in 

the Dutch Wadden Sea in August-October 1992. Wader Study Group Bulletin 68:20–22. 

Kraeuter, J. N., and S. R. Fegley. 1994. Vertical disturbance of sediments by horseshoe crabs 

(Limulus polyphemus) during their spawning season. Estuaries 17:288–294. 

Kvist, A., Å. Lindström, M. Green, T. Piersma, G. H. Visser. 2001. Carrying large fuel loads 

during sustained flight is cheaper than expected. Nature 413:730–732. 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 65 

Lafferty, K. D. 2001. Birds at a Southern California beach: seasonality, habitat use and 

disturbance by human activity. Biodiversity and Conservation 10:1949–1962. 

Lindström, Å, and T. Piersma. 1993. Mass changes in migrating birds: the evidence for fat and 

protein storage re-examined. Ibis 135:70-78. 

Lutcavage, M. 1981. The status of marine turtles in Chesapeake Bay and Virginia coastal 

waters. M. S. Thesis, College of William and Mary, Williamstown, Virginia. 126 pp. 

Lutcavage, M., and J. A. Musick. 1985. Aspects of the biology of sea turtles in Virginia. 

Copeia 1985:449–456. 

MacWhirter, B., P. Austin-Smith, Jr., and D. Kroodsma. 2002. Sanderling (Calidris alba). 

Pages 1–28 in A. Poole and F. Gill, editors. The birds of North America, No. 653. 

Academy of Natural Sciences, Philadelphia, and The American Ornithologists' Union, 

Washington D. C. 

Madsen, J. 1998. Experimental refuges for migratory waterfowl in Danish wetlands: I. Baseline 

assessment of the disturbance effects of recreational activities. Journal of Applied 

Ecology 35:386–397. 

*Maghini, M. K. R. 1996. Availability of contaminants to migratory shorebirds consuming 

horseshoe crab eggs on Delaware Bay beaches. Unpublished report, No. CBFO-C96-02, 

U. S. Fish and Wildlife Service, Chesapeake Bay Field Office, Annapolis, Maryland. 

*Manion, M. M., R. A. West, and R. E. Unsworth. 2000. Economic assessment of the Atlantic 

coast horseshoe crab fishery. Unpublished report, U. S. Fish and Wildlife Service, 

Division of Economics, Arlington, Virginia. 

*Meyer, S. R., J. Burger, and L. J. Niles. ND. Habitat use, spatial dynamics, and stopover 

ecology of red knots on Delaware Bay. Unpublished report, New Jersey Endangered and 

Nongame Species Program, Division of Wildlife, Trenton, New Jersey. 31 pp. 

*Millard, M. J., D. R. Smith, S. Michels, J. Brust, and J. Berkson. 2000. Stock assessment of 

Atlantic coast horseshoe crabs: a proposed framework. Unpublished report, Atlantic 

States Marine Fisheries Commission, Washington, D. C. 

*Minton, C., R. Jessop, P. Collins, and C. Hassell. 2002. Year 2001 Arctic breeding success, as 

measured by the percentages of first year birds in wader populations in Australia in the 

2001/02 Austral summer. Arctic Birds, Newsletter of the International Breeding 

Conditions Survey, International Wader Study Group. 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 66 

Mizrahi, D. S. 1999. Migratory behavior and ecophysiology of Semipalmated Sandpipers 

during spring migration stopover. Ph. D. dissertation. Clemson University, Clemson, 

South Carolina. 

*Mizrahi, D. S. 2002. Mass gain and stopover length in semipalmated and least sandpipers 

staging in Delaware Bay during spring migration. Unpublished report, New Jersey 

Audubon Society, Cape May Court House, New Jersey. 

Mizrahi, D. S., R. L. Holberton, and S. A. Gauthreaux, Jr. 2000. Patterns of corticosterone 

secretion in Semipalmated Sandpipers at a major stopover site during spring migration. 

The Auk 118:79-91. 

Morrison, R. I. G., R. E. Gill, Jr., B. A. Harrington, S. Skagen, G. W. Page, C. L. Gratto-Trevor, 

and S. M. Haig. 2001. Estimates of shorebird populations in North America. Occasional 

paper No. 104, Canadian Wildlife Service, Ottawa, Ontario. 64 pp. 

Morrison, R. I. G., and B. A. Harrington. 1992. The migration system of the red knot Calidris 

canutus rufa in the New World. Wader Study Group Bulletin 64 (supplement):71–84. 

*Morrison, R. I. G., and P. Hicklin. 2001. Recent trends in shorebird populations in the Atlantic 

provinces. Canadian Wildlife Service Bird Trends 8:16–19. 

Morrison, R. I. G., and R. K. Ross. 1989a. Atlas of nearctic shorebirds on the coast of South 

America, Volume 1. Canadian Wildlife Service, Ottawa, Ontario. 128 pp. 

Morrison, R. I. G., and R. K. Ross. 1989b. Atlas of nearctic shorebirds on the coast of South 

America, Volume 2. Canadian Wildlife Service, Ottawa, Ontario. 325 pp. 

Myers, J. P. 1983. Conservation of migrating shorebirds: staging areas, geographical 

bottlenecks, and regional movements. American Birds 37:23–25. 

Myers, J. P. 1986. Sex and gluttony on Delaware Bay. Natural History 95:68–77. 

*Nascimento, I. 2001. Migration and other biological data of Calidris canutus rufa from Brazil. 

Wader Study Group Bulletin 95:11 (abstract). 

*National Marine Fisheries Service. 2002. National Oceanic and Atmospheric Administration 

Fisheries 2001 Report. U.S. Department of Commerce, National Oceanic and 

Atmospheric Administration, National Marine Fisheries Service, Silver Spring, 

Maryland. 48 pp. 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 67 

Nettleship, D. N. 2000. Ruddy Turnstone (Arenaria interpres). Pages 1–32 in A. Poole and F. 

Gill, editors. The birds of North America, No. 537. Academy of Natural Sciences, 

Philadelphia, and The American Ornithologists' Union, Washington, D. C. 

*Niles, L. J., K. Clark, H. Sitters, C. Minton, A. Baker, A. Dey, N. Clark, D. Veitch, J. Burger. 

2003. Trends in mass gain and abundance of Red Knot (Calidris canutus rufa), Ruddy 

Turnstone (Arenaria interpres), and Sanderling (Calidris alba) on Delaware Bay, USA. 

Condor 105: submitted. 

*Niles, L. W., M. Peck, and R. Lathrop. 2001. Breeding habitat of the red knot in Nunavut, 

Canada. Wader Study Group Bulletin 95:14 (abstract). 

*Oring, L., B. Harrington, S. Brown, and C. Hickey (editors). 2000. National shorebird research 

needs: A proposal for a national research program and example high priority research 

topics. Unpublished report (see http://shorebirdplan.fws.gov). 

Peterman, R. M., and M. M’Gonigle. 1992. Statistical power analysis and the precautionary 

principle. Marine Pollution Bulletin 24:231-234. 

Pfister, C., B. A. Harrington, and M. Lavine. 1992. The impact of human disturbance on 

shorebirds at a migration staging area. Biological Conservation 60:115–126. 

Pfister, C., M. J. Kasprzyk, and B. A. Harrington. 1998. Body-fat levels and annual return in 

migrating semipalmated sandpipers. Auk 115:904–915. 

Piersma, T. 1996. Energetic constraints on the non-breeding distribution of coastal shorebirds. 

International Wader Studies 8:122–135. 

Piersma, T. 1997. Do global patterns of habitat use and migration strategies co-evolve with 

relative investments in immunocompetence due to spatial variation in parasite pressure? 

Oikos 80: 623-631. 

*Piersma, T. 2000. Energetics of body mass changes in red knots staging in Delaware Bay in 

May 1998. Unpublished report, Netherlands Institute for Sea Research, Trexel, The 

Netherlands. 

Piersma, T., and A. J. Baker. 2000. Life history characteristics and the conservation of 

migratory shorebirds. Pages 105-124 in L. M. Gosling and W. J. Sutherland, editors. 

Behaviour and Conservation. Cambridge University Press, London, England. 438 pp. 

Piersma, T., and N. Davidson (editors.). 1992. The migration of knots. Wader Study Group 

Bulletin 64 (supplement). 209 pp. 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 68 

Piersma, T., A. Hedenstroem, J. H. Bruggemann. 1997. Climb and flight speeds of shorebirds 

embarking on an intercontinental flight; do they achieve the predicted optimal behaviour? 

Ibis 139:299-304. 

Piersma T, G. A. Gudmunsson, and K. Lilliendahl. 1999. Rapid changes in the size of different 

functional organ and muscle groups during refueling in a long-distance migrating 

shorebird. Physiological Biochemical Zoology 72: 405–415. 

Pooler, P. S., D. R. Smith, R. E. Loveland, M. L. Botton, and S. F. Michels. 2003. Assessment 

of sampling methods to estimate horseshoe crab (Limulus polyphemus) egg density in 

Delaware Bay. Fisheries Bulletin 101: in press. 

Raveling, D. G., and E. A. Lefebvre. 1967. Energy metabolism and theoretical flight range of 

birds. Bird Banding 38:97–113. 

*Robinson, R. A., P. W. Atkinson, and N. A. Clark. 2003. Arrival and weight gain of Red 

Knots, Ruddy Turnstones, and Sanderlings staging in Delaware Bay in spring. British 

Trust for Ornithology Research Report No. 307, Thetford, Norfolk, United Kingdom. 55 

pp. 

Rodgers Jr, J. A., and S. T. Schwikert. 2002. Buffer-zone distances to protect foraging and 

loafing waterbirds from disturbance by personal watercraft and outboard-powered boats. 

Conservation Biology 16:216–224. 

Rodgers Jr, J. A., and H. T. Smith. 1997. Buffer zone distances to protect foraging and loafing 

waterbirds from human disturbance in Florida. Wildlife Society Bulletin 25:139–145. 

Shuster, C. N., Jr. 1982. A pictorial review of the natural history and ecology of the horseshoe 

crab, Limulus polyphemus, with reference to other Limulidae. Pages 1-52 in J. 

Bonaventura, C. Bonaventura, and S. Tesh (editors). Physiology and biology of 

horseshoe crabs: studies on normal and environmentally stressed animals. Alan R. Liss, 

Inc., New York, New York. 

*Shuster, C.N., Jr. 1996. The Delaware Bay area—an ideal habitat for horseshoe crabs. 

Unpublished report, Public Service Electric and Gas Company, Hancocks Bridge, New 

Jersey. 26 pp. 

Shuster, C. N., Jr., and M. L. Botton. 1985. A contribution to the population biology of 

horseshoe crabs, Limulus polyphemus (L.), in Delaware Bay. Estuaries 8:363–372. 

*Sitters, H. 2001. Behavioral evidence that shorebirds may suffer shortages of available 

horseshoe crabs’ eggs in Delaware Bay. Wader Study Group Bulletin 95:14 (abstract). 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 69 

Sitters, H. P., P. M. Gonzalez, T. Piersma, A. J. Baker, and D. J. Price. 2001. Day and night 

feeding habitat of red knots in Patagonia: Profitability versus safety. Journal of Field 

Ornithology 72:86–95. 

Smit, C. J., and G. J. M. Visser. 1993. Effects of disturbance on shorebirds: a summary of 

existing knowledge from the Dutch Wadden Sea and Delta Area. Wader Study Group 

Bulletin 68:6–19. 

*Smith, D. R., and S. Bennett. 2003. Horseshoe carb spawning activity in Delaware Bay: a 

preliminary report on 2002 and a comparison from 1999 to 2002. Unpublished report, 

 U. S. Geological Survey, Kearnysville, West Virginia. 

*Smith, D. R., N. Jackson, S. Love, K. Nordstrom, R. Weber, and D. Carter. 2002a. Beach 

nourishment on Delaware Bay beaches to restore habitat for horseshoe crab spawning and 

shorebird foraging. Unpublished report, The Nature Conservancy, Delaware Bayshores 

Office, Wilmington, Delaware. 51 pp. 

Smith, D. R., P. S. Pooler, R. E. Loveland, M. L. Botton, S. F. Michels, R. G. Webber, and D. B. 

Carter. 2002b. Horseshoe crab (Limulus polyphemus) reproductive activity on Delaware 

Bay beaches: interactions with beach characteristics. Journal of Coastal Research 18: in 

press. 

Smith, D. R., P. S. Pooler, B. L. Swan, S. Michels, W. R. Hall, P. Himachak, and M. J. Millard. 

2002c. Spatial and temporal distribution of horseshoe crab (Limulus polyphemus) 

spawning in Delaware Bay: implications for monitoring. Estuaries 25:115–125. 

Snedecor, G. W., and W. G. Cochran. 1980. Statistical methods, seventh edition. Iowa State 

University Press, Ames, Iowa. 507 pp. 

*Southeastern Cooperative Wildlife Disease Study. 2002. Influenza viruses in gulls, terns, and 

shorebirds of the United States Atlantic and Gulf coasts. Unpublished report, University 

of Georgia, Athens, Georgia. 

*Stillman, R. A., P. W. Atkinson, N. A. Clark, S. Gillings, I. G. Henderson, S. E. Love, R. A. 

Robinson, R. G. Weber, and S. L. Bardsley. 2003. Functional Responses of Shorebirds 

Feeding on Horseshoe Crab Eggs, Chapter 2. British Trust for Ornithology Research 

Report No. 308, Norfolk, United Kingdom. 41 pp. 

Sullivan, K. A. 1986. Influence of prey distribution on aggression on ruddy turnstones. Condor 

88:376–378. 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 70 

Takekawa, J. Y., and N. Warnock. 2000. Long-billed dowitcher (Limnodromus scolopaceus). 

Pages 1–20 in A. Poole and F. Gill, editors. The birds of North America, No. 493. 

Academy of Natural Sciences, Philadelphia, and The American Ornithologists' Union, 

Washington D. C. 

Thomas, K., R. G. Kvitek, and C. Bretz. 2003. Effects of human activity on the foraging 

behavior of sanderlings Calidris alba. Biological Conservation 109:67-71. 

*Truitt, B. R., B. D. Watts, B. L. Brown, and W. Dunstan. 2001. Red knot densities and 

invertebrate prey availability on the Virginia barrier islands. Wader Study Group 

Bulletin 95:12 (abstract). 

Tsipoura, N., and J. Burger. 1999. Shorebird diet during spring migration stopover on Delaware 

Bay. Condor 101:635-644. 

Underhill, L. G., R. P. Prís-Jones, E. E. Syroechkovski, Jr., N. M. Groen, V. Karpov, H. G. 

Lappo, M. W. J. Van Roomen, A. Rybkin, H. Schekkerman, H. Spiekman, and R. W. 

Summers. 1993. Breeding of waders (Charadrii) and Brent Geese Branta bernicla 

bernicla at Pronchishcheva Lake, northeastern Taimyr, Russia, in a peak and a decreasing 

lemming year. Ibis 135:277–292. 

*U. S. Army Corps of Engineers. 1991. Delaware Bay coastline, New Jersey and Delaware — 

reconnaissance report. Unpublished report, Philadelphia, Pennsylvania. 

*U. S. Army Corps of Engineers. 1997. Villas and vicinity, NJ — interim feasibility study, 

draft feasibility report and environmental assessment. Unpublished report, Philadelphia, 

Pennsylvania. 

*U. S. Fish and Wildlife Service. 2002. Birds of conservation concern 2002. Unpublished 

report, U. S. Fish and Wildlife Service, Division of Migratory Bird Management, 

Arlington, Virginia. 99 pp. 

Walls, E. A., J. Berkson, and S. A. Smith. 2002. The horseshoe crab, Limulus polyphemus: 200 

million years of existence, 100 years of study. Reviews in Fisheries Science 10:39-73. 

Warnock, N., and R. E. Gill, Jr. 1996. Dunlin (Calidris alpina). Pages 1–24 in A. Poole and F. 

Gill, editors. The birds of North America, No. 203. Academy of Natural Sciences, 

Philadelphia, and The American Ornithologists' Union, Washington D. C. 

*Weber, R. G. 2001. Horseshoe crab egg densities observed on six Delaware beaches in 2001. 

Unpublished report, Delaware National Estuarine Research Reserve, Dover, Delaware. 

24 pp. 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 71 

*Weber, R. G. 2002. Preconstruction horseshoe crab egg density monitoring and habitat 

availability at Kelly Island, Port Mahon, and Broadkill Beach study areas, Delaware. 

Unpublished report, Delaware National Estuarine Research Reserve, Dover, Delaware. 

23 pp. 

West, A. D., J. D. Goss-Custard, R. A. Stillman, R. W. G. Caldow, S. E. A. le V. dit Durell, and 

S. McGrorty. 2002. Predicting the impacts of disturbance on shorebird mortality using a 

behavior-based model. Biological Conservation 106:319–328. 

Wilson, J. R., A. A. F. Rodrigues, and D. M. Graham. 1998. Red knots (Calidris canutus rufa) 

and other shorebirds on the north central coast of Brazil in April and May 1997. Wader 

Study Group Bulletin 85:41–45. 

Woodard, J. C., D. J. Forrester, F. H. White, J. M. Gaskin, and N. P. Thompson 1977. An 

epizootic among knots (Calidris canutus) in Florida. I. Disease syndrome, histology and 

transmission studies. Veterinary Pathology 14:338-350. 

Zöckler, C., and I. Lysenko. 2000. Water birds on the edge. World Conservation Monitoring 

Center, World Conservation Press, Cambridge, U. K. 20 pp. 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 72 

14.0. TABLES

Table 4.1. Reference period landings, quotas, and annual harvest of horseshoe crabs in Atlantic coast states 

(Atlantic States Marine Fisheries Commission, Horseshoe Crab Technical Committee, unpublished data).

 1995–97 

reference 

Quota1

(-25%) 1998 1999 2000 2001 20022

Maine 13,500 13,500 13,500 1,500 1,391 100 0

New Hampshire 350 350 200 350 180 0 120

Massachusetts 440,503 330,377 400,000 545,715 272,930 134,143 138,613

Rhode Island 26,053 26,053 0 26,053 13,809 3,490 3,886

Connecticut 64,919 48,689 34,583 45,050 15,921 11,508 32,080

New York 488,362 366,272 352,462 394,026 628,442 126,336 177,052

New Jersey 604,049 453,037 241,456 297,680 398,629 261,239 281,134

Pennsylvania 0 - 75,000 - 0 0 0

Delaware 482,401 361,801 479,634 402,913 248,938 243,489 298,318

Maryland 613,225 459,919 114,458 134,068 152,275 170,653 278,211

Potomac River Fisheries 

Commission 0 - - - 0 0 0

District of Columbia 0 - - - 0 0 0

Virginia 203,326 152,495 1,015,700 650,640 145,465 48,880 36,525

North Carolina 24,036 24,036 24,036 25,602 14,973 9,130 11,115

South Carolina 0 - - - 0 0 0

Georgia 29,312 29,312 - 29,312 0 0 0

Florida 9,455 9,455 5,920 11,505 10,462 0 200

Total landings 2,756,949 2,564,414 1,903,415 1,008,968 1,257,254

% reduction total 8 15 37 66 58

% reduction New Jersey 60 51 34 57 53

% reduction Delaware 1 16 48 49 38

% reduction Maryland 81 78 75 72 55

1

 States that qualify for de minimis status are not required to reduce landings by 25%. 2

 2002 harvest information in incomplete for a number of states. 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 73 

Table 4.2. Changes in mean captures of horseshoe crabs (geometric means of catch per unit 

effort) on trawl surveys in Delaware Bay and along the Atlantic coast (National Marine Fisheries 

Service fall trawl survey). Periods were selected to correspond to initiation of intensive work on 

shorebirds in Delaware Bay (Andres analysis; see Figure 1–3 ). Standard errors only include 

among-year variance. 

Survey Period mean " SE n t df1 P

30-foot trawl (all crabs) 1990–1996 3.57 " 0.80 7 -2.99 8 <0.025

 1997–2002 1.09 " 0.24 6 

16-foot trawl (<160 mm) 1992–1996 0.48 " 0.09 5 -1.95 10 <0.09

 1997–2002 0.25 " 0.07 6 

16-foot trawl 1992–1996 0.41 " 0.15 5 -1.80 5 <0.14

(young-of-the-year) 1997–2002 0.13 " 0.04 6 

NMFS fall trawl 1990–1996 0.29 " 0.04 7 -1.55 10 <0.16

 1997–2000 0.20 " 0.04 4 

1

 degrees of freedom calculated from Sattherwaite’s method (Snedecor and Cochran 1980:97) 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 74 

Table 5.1. Coarse population estimates of North American-breeding shorebirds from the late 

1980s/early 1990s (Morrison et al. 2001). Five levels of confidence (low, low-moderate, 

moderate, moderate-high, high) in the data used to generate population estimates was scored for 

each species.

Species subspecies North America Eastern NA Confidence 

Ruddy Turnstone A. i. morinella 180,000 138,600 moderate 

Red Knot C. c. rufa 170,000? 150,000 moderate 

Sanderling – 300,000 116,000 low-moderate 

Semipalmated Sandpiper – 3,500,000 994,600 low-moderate 

Least Sandpiper – 600,000 101,900 low 

Dunlin C. a. hudsonia 225,000 138,300 low-moderate 

Short-billed Dowitcher L. g. griseus 110,000 110,000 low-moderate 

Long-billed Dowitcher – 500,000 11,300 low 

Table 5.2. Annual population size and variability of red knots in the western Atlantic flyway. Estimates derived 

from mark re-sighting data (Harrington 2002*).

 1981 1982 1983 1985 1986 1987 1988 1989 1990 

Mean 212,885 163,563 125,992 157,884 181,778 148,195 167,523 142,983 59,215 

Std. dev. 49,576 35,755 30,777 47,804 37,738 53,739 47,364 50,305 16,085 
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 75 

Table 5.3. Aerial survey counts of red knots from southern South America 

(Morrison and Ross 1989a, Morrison et al. unpublished data). 

Year Bahia Lomas, 

Chile 

Tierra del Fuego, 

Argentina/Chile 

Tierra del 

Fuego/Patagonia 

1982/85 42,762 53,232 67,496

2000 45,705 51,255 –

2001 29,745 – –

2002 22,172 27,242 29,271
Delaware Bay Shorebird Assessment Report and Peer Review - June 2003 76 

Table 5.4. Maximum counts of shorebirds made on spring aerial surveys of Delaware Bay 

beaches, 1986-2002 (Niles and Clark, unpublished data). 

Ruddy 

turnstone 

Red knot Sanderling Semipalmated

Sandpiper 

Dunlin Dowitcher 

spp. 

1986 88,234 58,156 16,193 285,802 8,054 166

1987 68,958 38,790 28,625 93,600 8,630 1,748

1988 58,390 34,750 41,055 177,110 2,030 2,980

1989 108,120 95,490 6,252 86,712 2,300 265

1990 32,301 45,860 5,378 48,185 2,875 1,130

1991 42,020 27,280 5,305 68,300 3,480 1,136

1992 53,930 25,595 7,330 42,630 11,245 6,335

1993 64,985 44,000 10,390 91,080 4,875 2,875

1994 80,795 52,055 9,955 95,180 12,165 5,045

1995 70,370 38,600 10,130 81,235 6,385 3,675

1996 47,115 19,445 8,355 41,190 8,740 8,330

1997 69,340 41,855 15,455 74,825 4,880 3,955

1998 101,660 50,360 23,520 67,745 16,305 6,830

1999 87,605 49,805 10,005 83,695 31,345 11,415

2000 69,000 43,145 20,815 100,635 39,935 10,185

2001 86,365 36,125 21,830 188,925 45,080 13,375

2002 64,690 31,695 13,835 51,320 32,305 13,000
Table 5.5. Difference in mean maximum counts of shorebirds made on spring aerial surveys of Delaware Bay be

1997-2002 (Niles and Clark unpublished data; Andres analysis). 

 Delaware Bay peak counts between periods 

 1986-1996 1997-2002 

mean " SE mean " SE t-value P df1 cor

Red Knot 43,638 " 6,239 42,164 " 3,015 -0.21 >0.20 15 Ruddy Turnstone 65,020 " 6,590 79,777 " 5,877 1.67 >0.40 16 Sanderling 13,543 " 3,410 17,577 " 2,158 0.10 >0.40 16 Semipalmated Sandpiper 101,002 " 21,652 94,524 " 20,032 -0.22 >0.40 16 Dunlin 6,434 " 1,083 28,308 " 6,150 3.50 <0.025 6 Dowitcher spp. 3,062 " 787 9,793 " 1,514 3.95 >0.40 9 

1 degrees of freedom calculated from Satterthwaite’s method (Snedecor and Cochran 1980:97). 
Table 5.6. Trends of selected shorebirds from analysis of International Shorebird Survey (ISS) data collected in eastern North America 

Maritime Shorebird Survey (MSS) data (Morrison and Hicklin 2001*), and Quebec checklist data collected during fall migration (Aubr

 Eastern North America Canadian MSS (adults) 

 ISS (1976–2000) 1970s – 1990s 1980s – 1990s Que % change 

P trend1 P trend1 P occu

Red Knot -1.65 >0.10 neg <0.01 neg <0.01 uncoRuddy Turnstone +1.05 >0.10 +/- >0.10 +/- >0.10 comSanderling -4.76 <0.01 +/- >0.10 +/- >0.10 comSemipalmated Sandpiper -3.88 <0.05 neg <0.01 neg <0.10 comLeast Sandpiper -6.90 <0.05 neg <0.001 +/- >0.10 comDunlin +0.21 >0.10 neg <0.05 neg <0.05 comShort-billed Dowitcher +1.26 >0.10 neg <0.001 neg <0.001 uncoLong-billed Dowitcher +0.47 >0.10 

–

–

–

– r

1 trends are indicated as negative (neg), positive (pos), or stable (+/-).
Table 6.1 Percentage of total numbers of birds observed on aerial surveys 

of Delaware Bay beaches relative to all International Shorebird Surveys 

(ISS) observations on the U. S. Atlantic coast (Harrington 2002*) and to 

coarse population estimates for the Atlantic flyway (see Table 5.1). 

Season % in Delaware Bay relative to 

 Species 

ISS data 

coarse population 

estimates 

Southward migration 

 Ruddy Turnstone 2.3 0.2

 Red Knot <0.1 <0.1

 Sanderling 0.4 0.4

 Semipalmated Sandpiper 8.71 2.5

 Least Sandpiper 

 Dunlin 5.6 3.8

 Short-billed Dowitcher 10.92 8.1

 Long-billed Dowitcher 

Northward migration 

 Ruddy Turnstone 47.5 78.0

 Red Knot 40.2 63.7

 Sanderling 34.4 35.4

 Semipalmated Sandpiper 50.01 28.72

 Least Sandpiper 

 Dunlin 39.7 32.6

 Short-billed Dowitcher 23.23 12.2

 Long-billed Dowitcher 

1

 includes all small Calidris sandpipers but is mainly semipalmated sandpipers. 

2

 53.2% if just the Bay of Fundy of Fundy population is included (Hicklin 1997). 

3

 includes both dowitcher species but is mainly short-billed dowitchers. 
Table 7.1. Average number of shorebirds observed in marine and non-marine 

habitats on International Shorebird Surveys (ISS) along the Atlantic coast, United 

States (Harrington 2002*). 

Season Average count Prominent 

 Species marine non-marine habitat P - value 

Southward migration n = 278 sites n = 323 sites 

 Ruddy Turnstone 7.29 0.22 marine <0.001

 Red Knot 22.33 0.05 marine <0.001

 Sanderling 84.63 0.99 marine <0.001

 Semipalmated Sandpiper 100.55 19.55 marine <0.001

 Least Sandpiper 16.17 25.08 >0.05

 Dunlin 24.70 2.76 marine <0.001

 Short-billed Dowitcher 22.70 6.74 marine <0.01

 Long-billed Dowitcher 1.25 19.19 >0.05

Northward migration n = 199 sites n = 322 sites 

 Ruddy Turnstone 31.90 1.55 marine <0.01

 Red Knot 24.45 2.04 marine <0.001

 Sanderling 52.92 3.37 marine <0.001

 Semipalmated Sandpiper 71.28 40.32 >0.05

 Least Sandpiper 19.89 17.51 >0.05

 Dunlin 119.01 33.42 marine <0.001

 Short-billed Dowitcher 24.68 4.70 marine <0.01

 Long-billed Dowitcher 5.56 4.47 >0.05
Table 7.2. Qualitative assessment of use of Delaware beaches by 

ruddy turnstones and red knots during spring migration (Carter 2002*). 

Delaware beach 

Ruddy 

turnstone Red knot 

Port Mahon EH1 R2

Pickering Beach H3 R 

Kitts Hummock EH H 

St. Jones River EH EH 

Bowers Beach EH H 

South Bowers EH EH 

Greco Canal Breach M4 H 

Mispillion Harbor EH EH 

Slaughter Beach H H 

1

 extremely high use - large flocks at all weather conditions. 

2

 occasional use - some individuals, not regular. 

3

 high use - large flocks in mild weather conditions. 

4

 moderate use - occasional large flocks intermittently. 
Table 8.1. Density of horseshoe crab eggs (eggs/m2

) on Delaware and New Jersey beaches in 1999 (Pooler et al. 

2003). 

 25–26 May 14–15 June 

State shallow (0-5 cm) deep (0-20 cm) shallow (0-5 cm) deep (0-20 cm) 

 Beach mean SE mean SE mean SE mean SE 

Delaware 

 Broadkill 0 0 764 749 611 183 51,795 30,772

 Prime Hook 102 41 41,711 38,793 3,769 1,049 114,031 57,112

 Fowler 51 25 917 331 1,375 621 107,614 59,364

 Slaughter 5,959 1,370 414,975 94,749 21,238 2,725 338,427 49,814

 Big Stone 51 25 5,755 2,592 357 270 12,325 7,268

North Bowers 11,714 3,305 486,984 119,267 53,527 11,989 203,922 36,063

 Kitts Hummock 13,445 4,192 165,572 40,046 7,741 2,796 63,560 22,378

 Woodland 255 87 51 31 3,565 1,874 31,016 15,152

New Jersey 

North Cape May 153 127 0 0 255 168 357 188

 South Cape Shore Lab 12,987 438 552,790 71,449 2,292 413 712,607 73,354

 Highs 1,070 362 574,792 49,397 2,241 479 741,943 88,516

 Kimbles 4,940 2,445 795,164 145,822 866 280 513,371 53,797

 Reeds 1,171 265 275,224 40,693 9,269 1,283 238,351 31,918

 Raybins 1,783 973 33,512 22,348 51 31 3,412 2,327

 Fortescue 1,019 219 328,954 55,366 10,492 1,961 237,179 98,620

 Sea Breeze 14,006 4,049 176,879 48,230 102 46 1,579 1,024
Table 8.2. Horseshoe crab egg densities (eggs/m2

) and 

percentage of eggs found in shallow (0–5 cm) sediments on 

Delaware beaches in 2001 (Weber 2001*). 

 9–11 May 25 May 

Beach eggs/m2 % shallow eggs/m2

Mispillion 502,000 23 530,000

St. Jones 121,000 12 –

Port Mahon 114,000 24 133,000

Old Pickering 60,000 8 21,000

Kitts Hummock 45,000 9 24,000

New Pickering 18,000 6 9,000

North Bowers 6,000 4 1,000

Kelly Island 873 50 13,000
Table 9.1. Numbers of gulls observed during aerial surveys of Delaware Bay beaches of New 

Jersey (Niles, unpublished data). 

 31 May 1990 29 May 1991 19 May 1992 26 May 2002 

Laughing gull 6,640 23,150 29,780 10,125

Herring/Black-backed gull 11,209 14,279 11,412 2,579

All gull species 17,849 37,429 43,644 12,704
Table 9.2. Time shorebirds were engaged in behaviors associated with foraging when the nearest 

neighbor was a gull or another shorebird in Delaware Bay 2002 (Burger et al. 2003*). 

 Focal species 

 red knot ruddy turnstone sanderling 

Pecks 

 sample size 177 808 145 

 overall mean 18.53 " 0.98 26.79 " 0.47 24.43 " 1.21 

 shorebird nearest neighbor 19.71 " 1.20 28.97 " 0.58 25.30 " 1.29 

 gull nearest neighbor 14.74 " 1.29 22.36 " 0.72 15.69 " 1.46 

Kruskal-Wallis P2

 (P) 2.61 (>0.05) 45.0 (0.0001) 5.45 (0.02) 

Foraging 

 sample size 297 1,259 246 

 overall mean 19.85 " 0.52 22.95 " 0.22 21.59 " 0.54 
 shorebird nearest neighbor 20.25 " 0.57 24.03 " 0.24 21.81 " 0.56 

 gull nearest neighbor 17.63 " 1.28 19.91 " 0.45 18.50 " 2.35 

Kruskal-Wallis P2

 (P) 3.82 (0.05) 78.3 (0.0001) 2.23 (>0.05) 

Vigilant 

 sample size 297 1,259 245 

 overall mean 3.62 " 0.35 2.55 " 0.14 1.47 " 0.24 

 shorebird nearest neighbor 3.12 " 0.36 1.88 " 0.14 1.50 " 0.25 

 gull nearest neighbor 6.33 " 1.02 4.44 " 0.34 1.07 " 0.70 

Kruskal-Wallis P2

 (P) 12.0 (0.0005) 80.5 (0.0001) 0.03 (>0.05) 

Aggressive interactions 

 sample size 290 1,232 245 

 overall mean 0.18 " 0.03 0.47 " 0.03 0.34 " 0.05 
 shorebird nearest neighbor 0.12 " 0.03 0.45 " 0.03 0.33 " 0.05 

 gull nearest neighbor 0.48 " 0.14 0.53 " 0.05 0.47 " 0.29 

Kruskal-Wallis P2

 (P) 9.73 (0.002) 9.81 (0.002) 0.001 (>0.05)
Table 10.1. Energetic requirements of shorebirds during spring migration in Delaware Bay (Casto and Myers 1993; Andres adjustment

 Lean 

mass 

(g) 

BMR 

(kJ/hr) 

Total energy 

expenditure1

(kJ) 

Energy

in fat 

(kJ)2 % fat

cost of 

 fat 

(kJ)3

Total energy need 

of an individual 

(expend.*fat cost) 

Population 

size4

Total energy need 

for the population

(kJ*108) 

c

Ruddy Turnstone 101 3.42 3,488 3,979 50 4,522 8,010 101,700 8.15 Red Knot 134 4.23 4,314 4,320 45 4,909 9,223 50,400 4.65 Semipalmated Sandpiper 25 1.23 1,254 657 40 746 2,001 188,900 3.78 Sanderling 50 2.05 2,091 4,597 70 5,223 7,314 23,500 1.72 Dowitcher spp. 100 3.39 3,458 2,627 40 2,985 6,443 45,100 2.91 Dunlin 55 2.19 2,234 1,447 40 1,642 3,875 13,400 0.52 1 2.5*BMR*(24 hours)*(17 days). 2 39.5 kJ/g of fat. 3 88% efficiency in depositing fat.4 highest maximum count 1997–2002. 5 70% assimilation efficiency. 6 10.25 kJ/g caloric equivalent of eggs. 
Table 11.1. Proportion of red knot catches (those >50 birds) at Mispillion Harbor, Slaughter 

Beach, Cook’s Beach and Reed’s Beach in Delaware Bay from 1997 to 2002 (Robinson et Al. 

2003*). 

 1997 1998 1999 2000 2001 2002 

Total number caught 893 1,086 2,431 1,145 2,234 1,349 

% at Mispillion, Slaughter, 

Cook’s, and Reed’s 1.00 0.73 0.68 0.36 0.74 0.95 

Table 11.2. Proportion of of red knot captures among time periods in Delaware Bay, 1997–2002 

(Robinson et al. 2003*). 

 10–14 May 15–19 May 20–24 May 25–30 May Total caught 

1997 0.00 0.00 0.79 0.21 893

1998 0.27 0.21 0.26 0.26 1,086

1999 0.18 0.13 0.24 0.45 2,431

2000 0.24 0.25 0.12 0.38 1,145

2001 0.09 0.13 0.47 0.31 2,234

2002 0.32 0.11 0.33 0.24 1,349
 

Table 11.3. Weekly counts of red knots, ruddy turnstones, and sanderlings made on aerial 

surveys (May–June) of Delaware Bay between 1997 and 2002 (Niles et al., unpublished data). 

week 1997 1998 1999 2000 2001 2002

Red Knot 

1 1721 787 0 0 3740 660

2 6445 16615 6670 765 23415 10170

3 21475 48945 18660 22960 36125 27330

4 41855 50360 49805 43145 32350 31695

5 9510 2920 10550 7160 7540 2323

Ruddy Turnstone 

1 3170 1100 170 185 935 4380

2 8690 11050 7960 6580 37705 31445

3 34465 47535 52610 43240 86365 56625

4 69340 101660 87640 69000 79310 64690

5 29537 16850 42685 36595 58840 6563

Sanderling 

1 2985 2880 3950 2526 3185 2779

2 3495 8950 6405 4640 8555 4540

3 8550 17715 7970 13510 21830 13765

4 15455 23520 9995 20815 8110 7872

5 3365 5400 10005 10050 12465 1980
Table 11.4 . The daily crude rate of mass gain of shorebirds (sample size) caught May 14 to May 28, 

1997–2002 in Delaware and New Jersey (Niles et al. 2003*). 

 Red knot Ruddy turnstone Sanderling 

 Delaware New Jersey Delaware New Jersey Delaware New Jersey 

1997 10.31 (876) – – 1.14 (659) – 1.93 (305) 

1998 7.32 (433) 5.62 (305) 5.89 (530) 3.53 (771) 1.21 (108) 1.04 (348) 

1999 2.94 (996) 3.02 (830) 1.02 (411) 3.72 (794) 0.25 (53) 1.23 (1,267) 

2000 2.19 (669) 4.38 (344) 3.32 (393) 3.59 (811) 0.13 (60) 1.09 (423) 

2001 4.22 (1,241) 4.76 (518) 3.35 (414) 3.23 (1,713) 1.66 (38) 1.29 (899) 

2002 2.33 (745) 2.62 (83) 3.32 (671) 3.20 (463) 1.35 (92) 2.09 (491) 
Table 11.5 Regression coefficients (b1) of best fit lines describing relationships between Julian date and mean fat 

mass of semipalmated sandpiper cohorts captured during spring migration stopovers along New Jersey's Delaware 

Bay coast. For each year, linear regression analyses were conducted for cohorts captured at Thompsons Beach only, 

and for Thompsons and Raybins Beaches combined. Data sets were truncated to include only cohorts captured on or 

after 17-18 May (Julian day 138). Analyses either assessed mean fat mass gain through the day of last capture, 

typically during the first week of June, or were truncated to describe the period of maximum fat mass gain. Analysis 

of covariance detected significant differences among regression coefficients within each analysis category. Students 

t-tests were used to determine pairwise differences between $1 coefficients within each category and controlled for 

experimentwise error related to multiple comparisons by using Bonferroni corrections for a. Overall, ten 

comparisons were made, resulting in an adjusted a of 0.005. Within analysis categories, values in "$1" columns 

with the same letter are not statistically different. 

All capture days $day 138 Period of maximum gain 

 period end period end

 Year β1 SE R2 (Julian day) b1 SE R2 (Julian day)

Thompson’s Beach 

 1996 1.14a 0.10 0.95 150 1.18a 0.12 0.91 149

 1997 0.49b 0.05 0.87 156 0.58b 0.06 0.89 151

 2000 0.18c 0.05 0.46 154 0.18c 0.05 0.46 152

 2001 0.53bd 0.08 0.85 151 0.53bd 0.08 0.85 151

 2002 0.08*bcd 0.19 0.08 147 0.60abcd 0.06 0.97 144

Thompson’s/Raybins Beaches 

 1996 0.9294a 0.0986 0.86 153 1.1829a 0.1194 0.91 149

 1997 0.4891b 0.0502 0.87 156 0.5785b 0.0575 0.89 151

 2000 0.3239b 0.0651 0.58 157 0.3239b 0.0651 0.58 157

 2001 0.5323ab 0.0792 0.85 151 0.5323b 0.0792 0.85 151

 2002 0.2874b 0.0755 0.49 156 0.3846b 0.1021 0.54 152

1 $1 not statistically significant 
15.0. FIGURES

Figure 1. Geometric mean, and 95% confidence intervals, of catch of all horseshoe crabs in the 

Delaware 30-foot trawl survey, 1990–2002 (S. Michels, unpublished data). 
Figure 2. Geometric mean, and 95% confidence intervals, of catch of juvenile (<160mm) 

horseshoe crabs in the Delaware 16-foot trawl survey, 1992–2002 (S. Michels, unpublished 

data). 
Figure 3. Geometric mean, and 95% confidence intervals, of catch of young-of-the-year 

horseshoe crabs in the Delaware 16-foot trawl survey, 1992–2002 (S. Michels, unpublished 

data). 
C. Shorebird Technical Committee Terms of Reference – 2002 

1.0. CHARGE AND IMMEDIATE ACTIONS

The purpose of the Shorebird Technical Committee (SBTC) is to provide technical advice to the 

Horseshoe Crab Fishery Management Board of the Atlantic States Marine Fisheries Commission 

on how horseshoe crab management actions might affect shorebird populations. The long-term 

tenure of the SBTC will be determined by the need to provide technical support to the 

Management Board. Therefore, these Terms of Reference will be reviewed annually and revised 

as needed. 

The immediate task of the SBTC is to oversee the production of a peer-reviewed report that 

synthesizes current literature and data on the status of shorebirds in Delaware Bay and to 

determine their energetic dependency on horseshoe crab eggs. The SBTC will review the report 

and draft a summary and recommendations from the results. The SBTC will also identify and 

prioritize research and monitoring needed for the conservation of Delaware Bay’s shorebirds. 

2.0. MEMBERSHIP

2.1. Members 

Karen Bennett Shorebird biologist, Delaware Division of Fish and Wildlife 

Gregory Breese Shorebird biologist, U. S. Fish and Wildlife Service 

Joanna Burger Shorebird biologist, Rutgers University 

David Carter Shorebird biologist, Delaware Coastal Management Program 

Robert Gorrell Fisheries biologist, National Marine Fisheries Service 

Brian Harrington Shorebird biologist, Manomet Center for Conservation Sciences 

Marshall Howe Shorebird biologist, U. S. Geological Survey 

Stewart Michels Fisheries biologist, Horseshoe Crab Technical Committee 

Mike Millard Fisheries biologist, U. S. Fish and Wildlife Service 

David Mizrahi Shorebird biologist, New Jersey Audubon Society 

Lawrence Niles Shorebird biologist, New Jersey Division of Fish and Wildlife 

Nellie Tsipoura Shorebird biologist, National Resource Defense Council (formerly) 

 

2.2. Official Observers

Alan Baker Shorebird biologist, Royal Ontario Museum 

Carrie Selberg/Brad Spear ASMFC Horseshoe Crab Fishery Management Plan Coordinator 

2.3. Coordinator/Facilitator 

Brad Andres Shorebird biologist, U. S. Fish and Wildlife Service 
3.0. Operations

The U. S. Fish and Wildlife Service will coordinate and facilitate operation of the SBTC and will 

be responsible for setting meeting agendas, distributing information, and ensuring actions 

identified by the SBTC are implemented. Immediate responsibility of coordination and 

facilitation of the SBTC lies with the National Shorebird Coordinator within the Division of 

Migratory Bird Management. Administration of the SBTC may be transferred to the regional U. 

S. Fish and Wildlife Service office in the future. 

Agreement on actions taken by the SBTC will be reached by consensus. If a consensus opinion 

can not be reached, majority and minority opinions will be drafted. Weight of the support of 

each opinion will be noted (e.g., 9 of 11 members present). Official observers, who are agreed 

on by members, can participate in discussions, but will not draft committee opinions or be 

included in enumeration of opinion support. A quorum of 8 of 11 members is needed to conduct 

official SBTC business. Alternates can be chosen to represent members at meetings. Changes to 

the Terms of Reference will be accepted by members as above. 

SBTC members are expected to attend 1-3 meetings annually and to provide a thorough review 

of the synthesis report. Meetings are open, but discussion can be limited to SBTC members and 

official observers. State and federal management agencies are expected to cover staff and travel 

costs to attend meetings. Non-governmental and university participants will be compensated for 

travel expenses. A representative of the State of Maryland may be added to the SBTC in the 

future. 

4.0. Budgets

4.1. FY2002 (1 Oct 2001 - 30 Sep 2002)

Travel to committee meetings (2) $4,000 (NJ DFW) 

Peer Review contracts $6,000 (DE DNREC) 

Contracts to report authors $25,000 (US FWS) 

4.2. FY2003

Travel to committee meetings (2) $6,000 (US FWS) 

Peer Review travel $12,000 (4K-DE DNREC; 6K-NJ DFW; 2K-US FWS) 

4.3. FY2004 and annually thereafter

Travel to committee meetings (2) $6,000 (US FWS) 
5.0. Addresses, Phone Numbers, and E-mails of SBTC Members and Observers

Brad A. Andres 

National Shorebird Coordinator 

U.S. Fish and Wildlife Service 

Division of Migratory Bird Management 

4401 North Fairfax Drive, MBSP 4107 

Arlington, VA 22203 

Phone: 703-358-1828; fax: 2217 

E-mail: Brad_Andres@fws.gov 

Allan Baker 

Head 

Centre for Biodiversity and Conservation Biology 

Royal Ontario Museum 

100 Queen’s Park 

Toronto, Ontario, Canada M5S 2C6 

Phone: 416-586-5520; fax: 

E-mail: allanb@rom.on.ca 

Karen Bennett 

Program Manager 

Delaware Division of Fish and Wildlife 

Natural Heritage Program/Nongame and Endangered Species Program 

4876 Hay Point Landing Rd. 

Smyrna, DE 19977 

Phone: 302-653-2880; fax: 302-653-3431 

E-mail: karen.bennett@state.de.us 

Gregory Breese 

Senior Staff Biologist 

Delaware Bay Estuary Project 

U. S. Fish and Wildlife Service 

2610 Whitehall Neck Road 

Smyrna, DE 19977 

Phone: 302-653-9152; fax: 9421 

E-mail: Gregory_Breese@fws.gov 
Joanna Burger 

Professor 

Nelson Biology Lab 

Rutgers University 

604 Allison Road 

Piscataway, NJ 08854-8082 

Phone: 732-445-4318; fax: 

E-mail: burger@biology.rutgers.edu 

David Carter 

Environmental Program Manager II 

Division of Soil and Water Conservation 

Delaware Department of Natural Resources and Environmental Control 

89 Kings Highway 

Dover, DE 19901 

Phone: 302-739-3451; fax: 2048 

E-mail: dcarter@dnrec.state.de.us 

Robert Gorrell 

Fishery Biologist 

Office of Sustainable Fisheries 

National Marine Fisheries Service 

1315 East West Highway, #13463 

Silver Spring, MD 20910 

Phone: 301-713-2341 ext. 150; fax: 9113 

E-mail: Robert.Gorrell@noaa.gov 

Brian Harrington 

Senior Scientist 

Manomet Center for Conservation Sciences 

PO Box 1770 

Manomet, Massachusetts 02345 

Phone: 508-224-6521; fax: 9220 

E-mail: bharr@manomet.org 
Marshall Howe 

Chief, Monitoring Program 

Patuxent Wildlife Research Center 

U. S. Geological Survey 

12100 Beech Forest Road, 

Laurel, MD 20708-4038 

Phone: 301-497-5858; fax: 5784 

E-mail: Marshall_Howe@usgs.gov 

Stewart Michels 

Chair, Horseshoe Crab Technical Committee 

Fisheries Section 

Delaware Division of Fish and Wildlife 

89 Kings Highway 

Dover, DE 19901 

Phone: 302-739-4782; fax: 6780 

E-mail: Stewart.Michels@state.de.us 

Mike Millard 

Fishery Ecologist 

Northeast Fishery Center 

U. S. Fish and Wildlife Service 

308 Washington Ave. 

Lamar, PA 16848 

Phone: 570-726-4247; fax: 2416 

E-mail: Mike_Millard@fws.gov 

David Mizrahi 

Vice President for Research 

Cape May Bird Observatory 

New Jersey Audubon Society 

600 Route 47 North 

Cape May Court House, NJ 08210 

Phone: 609-861-0700; fax: 1651 

E-mail: dmizrahi@njaudubon.org 
Lawrence Niles 

Chief 

Endangered and Nongame Species Program 

New Jersey Division of Fish and Wildlife 

P. O. Box 400 

Trenton, NJ 08625-0400 

Phone: 609-292-9400; fax: 1414 

E-mail: lniles@dep.state.nj.us 

Carrie Selberg/Braddock Spear 

Horseshoe Crab Fishery Management Plan Coordinator 

Atlantic States Marine Fisheries Commission 

1444 “I” Street, 6th Floor 

Washington, DC 20005 

Phone: 202-289-6400; fax: 6051 

E-mail: cselberg@asmfc.org/bspear@asmfc.org 

Nellie Tsipoura 

Biologist 

Water and Coastal Programs 

National Resource Defense Council 

40 West 20 Street 

New York, NY 10011 

Phone: 212-727-4539; fax: 1773 

E-mail: ntsipoura@nrdc.org