1 

REPRODUCTIVE SUCCESS OF OSPREY 

(PANDION HALIAETUS) NESTING IN THE 

VICINITY OF THE CHALK POINT OIL SPILL 

Final Report 

November, 2001

Introduction 

On April 7, 2000, approximately 126,000 gallons of a mixture of #2 and #6 fuel oil were 

released from a break in a pipeline providing fuel to the Chalk Point Generating Station. The 

pipeline was owned by the Potomac Electric Power Company (PEPCO) and operated by Support 

Terminal Services Operating Partnership, LP (ST Services). The spill initially leaked into a 

Spartina spp. dominated brackish wetland located in Swanson Creek, a tidal tributary of the 

Patuxent River. The marsh covers approximately 45 acres adjacent to the PEPCO Chalk Point 

facility. Extensive oiling of the wetlands within Swanson Creek took place during the first two 

days of the spill. On April 8, high winds, rain, and tides resulted in the oil being blown over 

containment booms and into the Patuxent River and its tributaries. The spill spread 

approximately 17 linear miles downstream in the Patuxent River and into several downstream 

tributaries, including Indian Creek, Trent Hall Creek, Washington Creek, and Cremona Creek, 

oiling approximately 40 miles of shoreline (Figure 1). In addition, water quality surveys 

indicated concentrations of petroleum products remained elevated above background levels in 

the Patuxent River for approximately 2-3 weeks following the spill (unpublished data). 

Shoreline clean-up activities, particularly in the most heavily impacted areas (e.g., Swanson 

Creek), continued through the summer and fall. 

Primary habitats impacted during the spill were wetlands, sandy beaches and associated open 

water areas. Several avian species that are dependent on aquatic habitats were nesting in the area 

at the time of the spill, including ospreys (Pandion haliaetus), federally threatened bald eagles 

(Haliaeetus leucocephalus), and great blue herons (Ardea herodias). The foraging strategies of 

these species and willingness to enter water and wetlands make them susceptible to oiling. 

Several oiled ospreys and great blue herons were observed by wildlife survey teams during the 

response effort. One of the concerns of the Natural Resource Trustees for the Chalk Point Oil 

was the potential effects of the oil spill on the reproductive success of these avian species. To 

this end, the objective of the present study was to evaluate the potential effects of the oil spill on 

the nesting success of ospreys. Other reports describe results of monitoring the nesting success 

of bald eagles and great blue herons. 

Study Organism and Susceptibility to Oiling 
2 

The osprey is one of the largest raptor species found within the Patuxent River region and at 

least 127 nesting pairs were documented along the river and its tributaries in 2000 (Steve 

Cardano, unpublished data). Ospreys are the only North American hawk species to feed almost 

exclusively on fish (Robbins and Blom 1996, Henny 1986, Reese, 1992). Demersal fish species 

inhabiting shallow waters, or deep water species frequenting surface waters, are most often taken 

by ospreys (Vana-Miller 1987). The foraging strategy of ospreys is to plunge feet first into the 

water and capture fish with their talons. In addition, Henny (in Palmer 1988) reports that 

ospreys bathe by plunge diving into the water. These behaviors make ospreys highly susceptible 

to oiling. During the first week of the Chalk Point spill, an osprey survey team composed of 

personnel from PEPCO and the Nanjemoy Creek Environmental Education Center observed ten 

oiled adult ospreys nesting within the spill zone. In addition, nesting materials in three nests 

associated with oiled adults were also observed to be oiled. 

Oil spills can have direct or indirect impacts on nesting birds. Adults that become oiled may 

transfer the oil from their plumage to their eggs during incubation. Refined oil may be highly 

toxic to avian embryos depending on the species; stage of embryonic development; and type, 

weathering, and dose of oil. Small quantities of oil on eggs can lead to embryo mortality, or 

cause deformities, especially during the early incubation phase (Albers 1991, 1995, Hoopes et al. 

1994). Studies have shown that as little as 1-20 uL of some types of oil can have lethal effects on 

developing embryos (Parnell et al. 1984, Hoffman 1990). Louisiana heron (Hydranassa tricolor) 

eggs treated with 10 uL of weathered crude oil had a reduced hatchability of 17% (Macko and 

King 1980). 

Habitat changes resulting from the extensive oiling of the tidal wetlands of Swanson Creek and 

other similar tributaries within the spill zone, may have reduced or contaminated prey species. 

Several studies have reported reproductive effects on avian species due to dietary exposure to 

petroleum-derived products (Coon and Dieter 1981, Ainley, et al. 1981). In addition, because 

ospreys require relatively clear, unobstructed water for successful foraging, any disturbance, 

natural (e.g., sedimentation and ripples caused by wind) or anthropogenic (e.g., oil sheens), that 

impacts the water’s surface may contribute to reduced prey visibility, and therefore reduced 

foraging success (Vana-Miller 1987, Poole 1989). During the Chalk Point spill, extensive 

sheening was observed throughout the middle Patuxent River region. 

Finally, human disturbances may also affect the reproductive success of ospreys. Nests exposed 

to human disturbances during the early phase of the nesting season have a higher likelihood of 

failure than non-disturbed nests (Vana-Miller 1987, Henny 1986). In addition, Swenson (1979) 

found that nests located in areas with minimal human disturbance have an increased likelihood 

of failure if disturbed suddenly during the later part of the nesting season. Increased boating and 

shoreline cleanup crew activities associated with the Chalk Point spill are examples of human 

disturbances that could have adversely affected osprey nesting success and productivity. 

Historical Population Surveys 

Data collection for determining osprey nesting success on the Patuxent River has been ongoing 
3 

since William Montgomery and Calvert Posey started surveying the population in 1973. The 

survey was initiated as a result of published reports from around the Chesapeake Bay and 

Mid-Atlantic region stating that ospreys were reproducing below normal levels, a result of 

exposure to DDT (Hoffman et al. 1995). In 1976, the Patuxent survey was taken over by the 

lead author of this report. Through the 1970s, osprey nests were examined at one to two week 

intervals. Each active nest was recorded using Postupalsky’s (1977) definition of an active nest, 

that is, the presence of eggs. Eggs were assumed to be in a nest if the female was low in the nest 

in the incubation position. From 1981 to1999 the nests were surveyed only once, at the end of 

June, when the chicks were approximately one to two weeks away from fledging. 

In the late 1970s and 1980s, it was apparent that ospreys were enjoying a considerable recovery 

from the effects of DDT. The Patuxent osprey population grew from 22 active nests in 1973 to 

over 100 nests in 1994. The focus of the survey had evolved from examining the effects of 

pesticides on the population to brood size reduction due to shortage of forage species. Food 

habits range considerably throughout this area. Menhaden (Brevoortia tyrannus) are the 

dominant food source in the more saline regions of the river while gizzard shad (Alosa 

sapidissima), catfish (Ictalurus spp.) American eel (Anguilla rostrata), and others make up the 

diet in the fresher zones of the river. In order to examine the effects, if any, of food supply on the 

nesting ospreys, the Patuxent River population was divided into three regions: an upper, middle 

and lower section. These sections are based on salinity regimes, and therefore, fish populations. 

 The upper section is considered tidal fresh (>0.5 ppt), and extends from Cocktown Creek/ Kings 

Landing to Western Branch (Figure 2a). The middle section is oligohaline (0.5 to 5.0 ppt) to low 

mesohaline (5.0 to 10ppt) and extends from Deep Landing to Broomes Island (Figure 2b), an 

area encompassing the majority of the spill zone (Figure1). The lower section is high mesohaline 

(10 to 15 ppt) and extends from Broomes Island, south to Drum Point (Figure 2c). These 

historical population surveys provided an excellent baseline for comparing the results of the 

present study. 

Methods 

The methodology for this assessment was developed cooperatively by the Wildlife Injury 

Workgroup for the Chalk Point Oil Spill Natural Resource Damage Assessment consisting of 

personnel from PEPCO, U.S. Fish and Wildlife Service (USFWS), the Maryland Department of 

Natural Resources, the U.S. Geological Survey’s Patuxent Wildlife Research Center and the 

Nanjemoy Creek Environmental Education Center (NCEEC) and is described in the Wildlife 

Injury Assessment Workplan for the Chalk Point Oil Spill (October 2000). The National 

Oceanic and Atmospheric Administration and the Maryland Department of the Environment also 

provided input to the assessment plan. In general, the approach was to monitor nests in the spill 

zone on a regular basis until fledging. To be consistent with the earlier surveys, the population 

was divided into the upper, middle and lower regions of the Patuxent River as described above. 

For comparative purposes, we assumed that ospreys nesting in the upper region of the river were 

not affected by the oil spill. This assumption is based on the distance of the spill site from the 

upper section and the expected foraging range of ospreys. The demarcation of the upper section 

is approximately 6 kilometers (4 miles) upstream of Swanson Creek. According to Clark (1995) 
4 

osprey foraging distances range from 2-5 kilometers (1.2 - 3.1 miles), but they will travel farther 

when food sources are scarce. Considering the abundance of fish within the Patuxent River 

system, the foraging range of Patuxent River ospreys is probably at the low to moderate end of 

that range. Based on this assumption, ospreys nesting in the upstream region were probably not 

foraging in areas impacted by the spill. 

Nest Surveys 

Osprey nests in the middle section were examined weekly or biweekly, beginning on April 11, 

2000 by personnel from PEPCO, NCEEC, and the Maryland National Capitol Parks and 

Planning Commission (MNCPPC). Regular monitoring of nests in the upper section was 

initiated in mid-May and nests in the lower section of the river were visited only once. During 

each visit, the number of eggs and/or young per nest were noted and recorded. Counts were 

accomplished by visual examination from a boat or using a mirror attached to a pole using 

methods similar to those used by Reese (1977) and Woodford et al. (1998). Monitoring was 

conducted through the end of June when the young began to fledge from the nest. In addition to 

the reproductive parameters that were recorded during each site visit, nests, adults and nestlings 

were also inspected for oiling. Active, but inaccessible nests, that is those nests that could not be 

reached for close inspection and banding, were recorded as "IA". Nest surveys were conducted 

on days when weather conditions, most notably winds, were favorable. The locations of all nests 

were recorded on navigational charts. 

 

Addled eggs were collected during the survey and archived in the event that petroleum 

hydrocarbon analysis was deemed necessary. Eggs were determined to be addled based on two 

criteria. First, the eggs had failed to hatch and the other nestlings in the same nest were two 

weeks of age or older. Second, when the failed egg was shaken gently, the contents felt 

liquefied. The egg was collected, wrapped in aluminum foil and sealed in a glass jar. The date 

and location of each egg was recorded on the aluminum foil. The jar was placed in a cooler and 

then placed in a freezer when the survey team returned to the PEPCO laboratory. All addled egg 

samples are presently in the custody of the USFWS Chesapeake Bay Field Office. 

Trapping Oiled Adults 

Ospreys that were determined to be moderately oiled were trapped, cleaned and returned to the 

nest. Ospreys were deemed moderately oiled when their entire underside, from legs to neck, 

were darkened by contact with oil. Typically, the feathers of adult males and females are white 

on the undersides. The females usually have a brown mottling or "necklace" across the chest 

that varies in intensity with individuals. The males may have some to no brown mottling across 

the chest. Since there is variation in the appearance of the brown necklace, careful observations 

were made to determine the extent, if any, of oil discoloration in these birds, especially females. 

Sexing ospreys also involves noting size (when comparable) and coloration on the dorsal side. 

The dorsal or backside of males is blackish and darker than a female’s. 
5 

Osprey were trapped using a modified "noose carpet". The trap was made of 1⁄2 inch square 

hardware cloth fashioned into a very shallow cone shape about 0.75 m in diameter. The cone 

shape provides strength and prevents contact with the eggs. Two fishing corks were attached to 

one edge to keep the trap from sinking if it became detached from the osprey. Approximately 

200 nooses made from monofilament fishing line were attached to the cone. After flushing the 

adult off the nest, the trap was placed in an inverted position over the eggs. When the adult 

returned to the nest, its feet became entangled in the monofilament nooses. When the bird 

attempts to fly from the nest, the weight of the noose carpet carries it into the water and prevents 

it from escaping. The trapped osprey was then retrieved from the water by the survey team. 

After being captured, the osprey (Figure 3) were transferred to waiting wildlife rehabilitation 

personnel for cleanup and release. If a female was captured, the male would return to the nest to 

assume incubating duties. In the case that both ospreys needed to be caught, the male was 

caught in the same manner as the female. The eggs from nests in which both adults were 

captured were either placed in foster nests or given to wildlife rehabilitation personnel and 

placed in incubators. Collected eggs were replaced on the nest just prior to the release of the 

adults. In an effort to minimize stress to oiled adult ospreys, all trapping occurred when the 

wind was calm and clear skies and mild temperatures prevented the chilling of exposed eggs. 

Where possible, oiled sticks and vegetation found in nests were removed. 

Data Analyses 

The data were summarized as follows: the number of active nests (total, accessible, with known 

outcomes); total eggs laid; percentage hatching; total young fledged; mean number of young 

fledged per active nest; total number of successful nests (those that fledged at least one nestling); 

and the mean number of young per successful nest. 

Nest success, defined in this study as at least one nestling successfully fledging per nest, of 

ospreys in the middle section of the river (spill impacted area) was compared to that in the upper 

section (unimpacted) in 2000 using the Mayfield method (Mayfield 1961, Mayfield 1975, Bart 

and Robson 1982). This analysis estimates a daily survival rate for nests in each section and 

controls the bias which may exist due to nests which failed before the collection of data began. 

Nests in the lower section of the river were not visited more than once and therefore daily 

survival rate could not be estimated for this section of the river. Program Mayfield, written by 

J.E. Hines (http://www.mbr. pwrc.usgs.gov:80/software.html) was used to perform the analysis 

specified in Bart and Robson (1982) to calculate the daily nest survival rates. Program Contrast 

(Hines and Sauer 1989) was used to compare the daily nest survival rates between the two river 

sections. Daily survival rates were estimated for both the egg and nestling stages. 

Loglinear models (Stokes et al. 1997) were used to compare the number of active nests and 

number of young per active nest (productivity) among years and among the three sections of the 

river. In essence, this analysis is similar to an analysis of variance, but is more appropriate for 

evaluating “count” data (Jeff Hatfield, personal communication). This analysis was performed 

for the complete set of data (1973-2000, excluding 1993 and 1998 because the lower river was 
6 

not surveyed then) and also just for 1999-2000. A value of 0.01 was substituted for cell 

combinations in which a zero count of nests was obtained. Nests with 3 or 4 chicks were 

combined into one category of 3 or more chicks, because of the small number of nests with 4 

chicks. 

Results 

 

During the nest survey, a total 127 active nests were identified, 103 of which had a known 

outcome, that is the fate of the nestlings through fledging was known (Table 1). In a few 

instances, nestlings had not yet fledged at the time monitoring was terminated; for these nests the 

outcome was unknown. 

A summary of the nesting data from the lower, middle (spill area) and upper river sections are 

presented in Table 1 (Details in Appendices A and B). The lower section recorded 41 active 

nests, 31 were accessible with a known outcome. Fifty-eight active nests were located in the 

middle section where the oil spill occurred, 44 were accessible with a known outcome. Five of 

the inaccessible nests (with no known outcome) were located on the PEPCO property. An 

independent survey conducted in August 2000 indicated that all the nests located on PEPCO 

property had been abandoned (Ann Wearmouth, personal communication). Survey of upper 

section nests located 28 active nests, two nests were inaccessible, but the fate of all nestlings was 

able to be determined (i.e., 28 nests with a known outcome). The upper region of the Patuxent 

osprey population was not directly affected by oil from the spill. 

In the lower section, 22 (71%) of the 31 active nests with a known outcome successfully fledged 

at least one young, with an average of 1.55 young per active nest (Table 1). The average number 

of young per successful nest was 2.18. In the middle section, 33 (75%) of the 44 active nests 

with a known outcome successfully fledged at least one young, with an average of 1.50 young 

per active nest. The average number of young per successful nest was 2.00. In the upper section, 

24 (86%) of the 28 active nests with known outcomes successfully fledged at least one young, 

with an average of 1.79 young per active nest. The average number of young per successful nest 

was 2.08. 

Affected Nests 

Eleven nests located within the middle section of the river were determined to be directly 

affected by the oil spill as evidenced by discoloration or oiling of adults or eggs, the presence of 

oiled nesting materials or proximity to high shoreline activity (Table 2). Seven (64%) of the 11 

nests successfully fledged at least one young, for an average of 0.91 young per nest. The 

average number of young per successful affected nest was 1.43 (Table 2). 

Ten adult osprey were observed to be oiled, four of these were successfully trapped. The four 

captured birds (two pairs) were given to wildlife rehabilitation experts for heath evaluations, 

appropriate cleanup, and rehabilitation. One pair and their eggs were successfully returned to the 

nest and subsequently raised two young. The other pair was displaced at the nest site by new 
7 

osprey and driven away. Several days later, the female of that pair was found dead near 

Persimmon Creek. The cause of death is unknown. A total of 6 addled eggs were collected and 

archived. 

Nest Success 

The daily survival rates for the egg stage were 0.9708 and 0.9891, respectively for upper and 

middle sections of the river, and 0.9963 and 0.9968, respectively for the upper and middle 

section nests in the nestling stage. There was no significant difference in nest success between 

the upper and middle sections of the river for either the egg stage (P=0.5192) or the nestling 

stage (P=0.8498) (Table 3). 

Nest Productivity 

For purposes of evaluating potential impacts of the oil spill on osprey production, what is of 

interest in the loglinear analysis are the interaction terms. Statistically significant interactions 

would indicate differences in the number of chicks (i.e., productivity) among years (chick*year), 

river sections (chick*section) or both (chick*year*section). Results indicated no statistically 

significant relationships (p> 0.05) between the number of chicks and the other variables, for the 

entire period 1973-2000 or for 1999-2000 (Table 4). The significance of the “chick” term in the 

1999-2000 interval indicates there are statistical differences in the number of young per nest 

when averaged across both year and river section. There was a significant effect of time (“year”, 

p=0.0025) in the data from 1973 - 2000, implying a trend over time in the number of active 

osprey nests during this period (Figure 4). The lack of significance (p=0.7466) of this term in 

1999-2000 implies no difference in the number of active osprey nests between these two years 

(Table 4). There were highly significant effects of river section over both time periods 

(p<0.0001 for 1973-2000, p=0.0096 for 1999-2000) indicating differences in the number of 

active osprey nests among the three sections of the river (Table 4). Finally, there was no 

significant interaction between time (“year”) and section (p= 0.8279 for 1973-2000, p=0.3543 

for 1999-2000) , suggesting that trends over time in the three sections of the river were similar 

over the period of the analysis (Table 4). 

Discussion 

Results of the monitoring study suggested that there were no detectable population-level impacts 

on the reproductive success of the ospreys nesting in the Patuxent River as a result of the April 7, 

2000 Chalk Point oil spill. The mean of 1.50 young fledged per active nest in the middle section 

was similar to the 25 year average of 1.51 for the river (Cardano, unpublished data) and 

exceeded values determined to maintain a stable population. Henny and Wight (1969) 

determined that 0.95-1.30 young were required to fledge per nest in order to maintain a stable 

breeding population. In 2000, and most other years of the Patuxent study (except 1976, 1978, 

and 1989), ospreys have met or exceeded this average (Figure 5). 
8 

Comparison of nesting success between the middle and upper sections of the river in 2000 via 

the Mayfield method indicated no significant statistical differences in daily survival rates in the 

egg stage or nestling stage. In addition, results of log-linear analysis indicated that there were no 

significant differences in the productivity between the years 1999-2000 and in the previous years 

(1973-1999) of the study. 

There is evidence that individual nests may have been adversely affected by the oil spill and 

associated clean-up activities. Of the ten ospreys that were observed to be discolored due to oil 

contact, two pairs of adults were trapped, cleaned, and released. One of those pair and their eggs 

were successfully returned to the nest and subsequently raised two young. The other pair was 

displaced at the nest site by new osprey and driven away. The female of this pair was later found 

dead, with the cause of death unknown. The new pair continued to incubate one of the three 

original eggs, which failed to hatch. The six other ospreys that were observed to be discolored 

by oil were not trapped for cleaning because of weather conditions, lack of eggs, or degree of 

discoloration. Three of those ospreys had preened the oil from their feathers and were noticeably 

cleaner by the end of the nesting season. 

A total of 10 young fledged from the 11 monitored nests directly affected by the oil or clean-up 

activities for an average of 0.91 young per nest (Table 2). The average number of young per 

successful oiled nests was 1.43. These values are lower than the averages calculated for the 

population in the middle section of the river, which were 1.50 young per active nest and 2.0 

young per successful nest, respectively. It was suspected that nest failure in one of the oiled 

nests could be due to its proximity to the oil spill cleanup efforts. The activity of workers near 

the nest may have kept the female away for long enough periods to cause the eggs to become 

cooled. Human disturbances near an active nest site in the early stages of incubation have been 

implicated in nest failure (Vana-Miller, 1987; Henny 1986). In addition, there were five active 

nests observed on PEPCO property that were inaccessible and not included in this study 

(Appendix A). An in-house survey conducted by PEPCO in the third week of August 2000 

indicated all nests on PEPCO property had been abandoned (Ann Wearmouth, formerly of 

PEPCO, personal communication). Although osprey in Chesapeake Bay may naturally abandon 

the nest by the second week of August (Chuck Henny, U.S. Geological Survey, Biological 

Resources Division, personal communication), in the absence of monitoring or anecdotal 

information pertaining to these nests, we assumed these nests were abandoned before producing 

young. Abandonment of the nests was probably due to the high incidence of human activity that 

took place near those nests. 

Because of the evidence suggesting localized effects of the oil spill on individual nests, we 

estimated the number of young lost from these nests in the following way. The number of 

affected nests was estimated to be 16 (11 that were monitored plus 5 nests on PEPCO property 

that were abandoned). The average number of young produced by unaffected nests was 1.70 (56 

young/ 33 unaffected active nests in the middle section). This estimate is different than the 

average young produced in the middle section of the river (1.50) because the data from the 11 

affected nests were deleted from the calculation. The expected number of young produced by 

affected nests was 27.2 (i.e., 16 nests * 1.70 young/nest). The observed number of young 
9 

produced in affected nests (10) was then subtracted, for a loss of approximately 17 osprey young. 

 

Acknowledgments 

This report was prepared by Steve Cardano of the Nanjemoy Environmental Education Center 

and edited by Ann Wearmouth (formerly of PEPCO), Peter McGowan and Beth McGee 

(USFWS Chesapeake Bay Field Office). The document was reviewed by the Wildlife Injury 

Workgroup for the Chalk Point NRDA Council. We thank Jeff Hatfield of the Patuxent Wildlife 

Research Center (USGS/Biological Resources Division) for statistical analysis of the data and 

Chuck Henny of the Forest and Rangeland Ecosystem Science Center (USGS/BRD) for 

conducting the peer review of the report. Osprey nests were monitored by Steve Cardano, Ann 

Wearmouth and Greg Kearns of the Maryland National Capitol Parks and Planning Commission. 

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Figure 1. Extent of shoreline oiling resulting from the Chalk Point Oil spill. 
Figure 2a. Map of upper Patuxent River region in which active osprey nests (n=28) were 

monitored for reproductive success during the PEPCO-Chalk Point oil spill in April, 

2000. 
Figure 2b. Map of middle Patuxent River region in which active osprey nests (n=58) 

were monitored for reproductive success during the PEPCO-Chalk Point oil spill in April, 

2000. 
Figure 2c. Map of lower Patuxent River region in which active osprey nests (n=41) were 

monitored for reproductive success during the PEPCO-Chalk Point oil spill in April, 

2000. 
Figure 3. Moderately oiled male adult osprey captured for cleaning and rehabilitation 

during the PEPCO, Chalk Point oil spill in April 2000. 
Table 1. Summary of reproductive measurements used to calculate nesting success for Patuxent River ospreys in 

Reproductive Measurement Lower

Section

Middle Section Upper Section All Sections

Total active nests 41 58 28 127Total accessible nests 33 44 26 103Total active nests w/ known outcome 31 44 28 103Total eggs laid nd 118 nd nd% Hatching nd 70 (83) nd ndTotal young fledged 48 66 50 164Ave. young fledged per active nest w/known outcome

1.55 1.50 1.79 1.59

Total number successful nests 22 (71%) 33 (75%) 24 (86%) 79 (77%)Ave. young per successful nest 2.18 2.00 2.08 2.08

 nd = no data. Regular monitoring in the upper and lower sections did not begin until the majority of eggs had h
Table 2. Number of young osprey fledged in nests that were: oiled and /or had adults that were oiled; eggs that a

were located in areas with high shoreline activity.

Nest

#

Location Comments Outcome

4 ONP Chalk Point adults oiled/cleaned and released fledged 2

5 Pylon "A" Chalk Point oiled vegetation/male oiled legs to head fledged 26 Pylon "B" Chalk Point oiled veg./oiled adults trapped&cleaned/pair replaced/female found dead fledged 0

7 Pylon "C" Chalk Point eggs found to be darker than normal fledged 1

10 ONP s Hunting Creek female oiled on chest and neck fledged 223 ONP Buena Vista two eggs discolored a muddy gray fledged 127 ONP Indian Creek oiled veg. in nest/ high clean-up activity/ one egg muddy-gray fledged 1

29 Chan. Mrk. #25 Teague Pt. female with oil on legs/ one egg discolored muddy-gray fledged 030 Chan. Mrk. #23 Long Pt. adults lightly oiled/ eggs darker brown than normal fledged 032 ONP Persimmon Creek high clean-up activity along shoreline fledged 052 old pilings at Sandy Point female oiled/ collected two addled eggs fledged 1

Note: ONP = On Nesting Platform
Table 3. Mayfield estimates of nest success for the upper and middle regions of the Patuxent

River in 2000 and results of statistical comparisons of survival rates.

Region

of

River

Daily survival

rate during egg

stage 

Survival rate

to hatchinga

(A)

Daily survival

rate during

nestling stage

Survival rate to

fledgingb

 (B)

Nest Success

(AxB)C

Upper 0.9708 0.3148 0.9963 0.8216 0.2586

Middle 0.9891 0.6522 0.9968 0.8438 0.5503

P-value - 0.5192 - 0.8498 -

a

 Calculated as daily survival rate to the 39th power accounting for a 3-day laying period and a

36-day incubation period.

b Calculated as daily survival rate to the 53rd power accounting for a 53 day fledging period.

C Defined as probability of an egg surviving to the fledging stage.
Table 4. Chi-square statistics, degrees of freedom (df), and p-values for terms in the loglinear

models (significant terms are in bold).

TERM

SURVEY YEARS

1973-2000 1999-2000

χ2 df P-value χ2 df P-value

Chick 1.78 3 0.6193 19.90 3 0.0002

Year 49.42 25 0.0025 0.10 1 0.7466

Chick*Year 38.82 75 0.9998 0.42 3 0.9357

Section 28.22 2 <0.0001 9.29 2 0.0096

Chick*Section 0.89 6 0.9894 1.95 6 0.9240

Year*Section 40.54 50 0.8279 2.07 2 0.3543

Chick*Year*

Section

128.02 150 0.9029 7.80 6 0.2531
Figure 4. Number of active osprey nests in the three sections of the Patuxent River, 1973 

- 2000. 

Year

1975 1980 1985 1990 1995 2000

Number of Active Nests

0

10

20

30

40

50

60

Lower Patuxent River

Middle Patuxent River

Upper Patuxent River
Figure 5. Mean productivity of active osprey nests in the upper, middle, and lower 

sections of the Patuxent River, 1973-2000.

Year

1975 1980 1985 1990 1995 2000

Mean Number of Chicks per Active Nest 1

2

3

Lower Patuxent River

Middle Patuxent River

Upper Patuxent River
Appendix A. Summary of osprey nest survey data collected in 2000 for the upper, middle, and lower Patuxent River 

y=young;F=female, M=male; IA=Inaccessible).

Nest # Substrate Location Apr 11 Apr 19 Apr 20 May 7 May 19 May 26 Jun 8 Jun 2

1 pilings Centerspan Rt. 231 Br. 1 2 2 2y 2y 2y 2y 2 ONP w end Rt. 231 Br. 2 3 3 2y 1e 3y 3y 2y 3 ONP Teague Point 3 3 1e 2y empty 4 ONP Chalk Point 3 3 2e 1y 2y 1e 2y 2y 2y 5 pylon A Chalk Point 3 3 1e 2y 3y 2y 2y 2y 6 pylon B Chalk Point 3 3 1 1 2 empty 7 pylon C Chalk Point 3 3 3 2y 1e 2y 2y 1y 8 pylon D Chalk Point 3 3 3 3y 3y 3y 3y 9 pylon on land - Calvert Side 

10 ONP s entrance Hunting Cr. 3 3 3y 2y 2y 2y 2y 11 ONP @ entrance Hunting Cr. 3 3 3 3y 3y 2y 2y 12 ONP inside Hunting Cr. 1 3 3 2y 1y 1y 1y 13 boathouse e Eagle Harbor 14 chnl. mk. # 32 Trueman Pt. 3 3 1y 2e 3y 3y 3y 15 ONP n Eagle Harbor 4 4 2y 2e 3y 1e 3y 3y 16 ONP Deep Landing 2y 2y 1y 17 boathouse Deep Landing 18 tower PEPCO property 19 tower PEPCO property 20 light pole coal yard PEPCO 21 light pole coal yard PEPCO 22 tele. pole near hatchery PEPCO 23 ONP Buena Vista 2 2 2 1y 1e 1y 1e 1y 1e 1y 24 ONP Welches, Benedict 4 3y 3y 3y 2y 
Nest # Substrate Location Apr 11 Apr 19 Apr 20 May 7 May 19 May 26 Jun 8 Jun 2

25 ONP Whitey, Benedict 3 3 2 1y 1e 1y 1e 1y 1y 26 tele. pole Benedict 27 ONP entrance, Indian Cr. 1y 1e 2y 2y 2y 2y 28 ONP n side Golden Beach 3 3y 3y 3y 3y 29 chnl. mk. # 25 Teague Pt. 3 3 1 empty 30 chnl. mk. #23 Long Point 3 3 empty 31 ONP Trent Hall, near house 32 ONP Persimmon Cr. 3 1 empty 33 ONP Cremona 3 3y 3y 2y 34 duckblind Marsh Pt. 3 3y 3y 3y 35 ONP inside Marsh Pt. 3 3y 3y 2y 36 ONP 2nd inside Marsh Pt 3 3y 3y 3y 37 ONP near Drift Inn 3 3y 3y empty 38 ONP Queentree Landing 2e 1y 1y 1e 1y 39 ONP s Cape St Mary's 2y 40 ONP s Sandgates 41 chnl. mrk. #1 Nans Cove 3y 1y 42 chnl. mrk. #3 Nans Cove 2y 1e 2y 43 ONP n Broome Island 3y 3y 44 ONP Brisco's n Broomes Is. 3y destr. 45 chn. mrk. # 18 Jack Bay 2y 1e 2y 2y 46 chn. mrk. # 3 Battle Creek 2 2 empty 47 ONP Battle Creek 3y 3y 3y 48 ONP old piling, Battle Creek 3y 3y 1y 49 old piling Sheridan Pt. 3 3 2y 50 chnl. mrk. # 21 Sheridan Pt. 3 2y 51 ONP Mac's Hollow 52 old piling Sandy Point 3 3 3 1y 53 boathouse Buzzard Is. Creek empty 54 old tree Buzzard Island 
Nest # Substrate Location Apr 11 Apr 19 Apr 20 May 7 May 19 May 26 Jun 8 Jun 2

55 sign Sea Gulls Nest 1 empty 2 56 ONP Hallowing Point 3 3 2y 1e 2y 1e empty 57 tree nest n Broomes Island 58 ONP s Deep Landing 

Lower Patuxent River, south of Broomes Island 

30-J

59 chnl. mrk. #5 Hog Point 2y 60 ONP Sea Plane Lndg. area 61 chnl. mrk. 6A Sandy Pt. 2y 62 chn. mrk. #6 1y 63 chnl. mrk. #2 Drum Point 64 ONP .25 m nw Drum Point 3y 65 chnl. mrk. #2 Solomon's Entrance empty 66 chnl. mrk. #3 Solomon's entrance 3y 67 chnl. mrk. Junction Bouy entrance 68 ONP Solomon's entrance 3y 69 chn. mrk. #2 Mill Creek 3y 70 crane LNG dock 71 chnl. mrk. #4 Mill Creek 3y 72 chnl. mrk. Junction Bouy Mill Cr. empty 73 chnl. mrk. #3 Mill Creek 2y 74 chnl. mrk. #3 CBL 1y 75 ONP s of ONP #76 2y 76 ONP @ Danger Shoal Mrk. 2y 77 chnl. mrk. entrance Town Creek 78 chnl. mrk. #2 Second Cove 3y 79 bridge pyl. s side of Rt. 4 Bridge 80 chnl. mrk. #8 Pt. Patience 2y 81 chnl. mrk. #9 
Nest # Substrate Location Apr 11 Apr 19 Apr 20 May 7 May 19 May 26 Jun 8 Jun 2

82 chnl. mrk. #11 83 chnl. mrk. #4 Clarkes Lndg. 2y 84 pilings Clarkes Lndg. 2y 85 ONP Clarkes Lndg. empty 86 ONP n Half Pone Point 87 ONP St. Cuthbert's Wharf empty 88 chnl. mrk. #13 empty 89 ONP n of mrk. # 13 90 chnl. mrk. # 15 Sotterly Point 2y 91 chnl. mrk. # 16 Broomes Is. empty 92 ONP Intake @ PANS 2y 93 chnl. mrk. #14 St. Leonard's Cr. 2y 94 ONP n side St.Helen's Cr. 2y 95 ONP s side St.Helen's Cr. 2y 96 ONP n of Hungerford Cr.. 2y 97 ONP at end of jetty,Hunger. 

Cr. 

2y 

98 ONP @old duckblind-Nav.rec empty 99 pilings n Pt. Patience 1y 

Upper Patuxent River, north of Deep Landing 

24-May 1-Jun 14-Jun 7-

100 ONP Gun Club-Jug Bay 2y 2y 2y 2y 101 ONP Jackson's Landing 2y 2y 2y 2y 102 ONP Bristol duckblind site 3 1y 2e 2y 2y 103 ONP Monday's Creek 3y 3y 104 ONP Western Branch #1 3y 1e 3y 3y 3y 105 ONP Galloway Creek 1y 2e 1y 2e 1y 2e 1y 106 ONP Lookout Creek 1y 1e 3y 107 ONP #2 Nottingham 2y 1e 1y 
108 ONP #1Nottingham 2 empty 

Nest # Substrate Location Apr 11 Apr 19 Apr 20 May 7 May 19 May 26 Jun 8 Jun 2

109 tree Shores of Calvert 3y 110 ONP Merkle WMA Driving 

Tour 

3y 3y 3y 3y 

111 ONP Merkle WMA 

boardwalk 

1 1y 1y empty 

112 Silo Merkle WMA 2y 113 ONP Merkle WMA Pier 1y 114 ONP Billingsly Creek 3y 115 ONP Railroad Creek 3y 3y 116 ONP Duttons Landing 1y 2e 3y 3y 3y 117 ONP Western Branch #2 3 3 3y empty 118 ONP Selby's Landing 1y 1y 1y 1y 119 ONP Hall's Creek 1y 120 tree Mattaponi Creek 2y 2y 2y 2y 121 ONP Selby's Island 2 2 1y 1e 1y 122 ONP Shores of Calvert 2y 2e 2y 1e 2y 2y 123 ONP JBWS s Glebe Marsh 3y 2y 2y 1y 124 ONP JBWS observation deck 2y 125 ONP JBWS RR 3y 3y 126 duckblind JBWS Swan Pt. 2y 2y 2y 2y 127 ONP Windsor 3y empty 
APPENDIX B: Summary of osprey monitoring activities 

April 11, 2000 

The first survey of the effects of the oil spill on the nesting ospreys occurred four days after the spill. Rain and 

inclement weather hampered early survey attempts in April and May. On April 11, 2000, 15 nests were examined in the 

spill area, 12 by boat and two by car. The contents of 12 nests could be examined. Three nests were inaccessible and 

those adults were not close enough to determine if they were discolored due to contact with oil. Three of the 12 nest sites 

examined were affected by oil. Nest number five contained some oiled sticks and small twigs. The adult male was 

moderately discolored from the legs to the head. Nest number six contained small spots of oil in the nest. The adult 

male's feet, which are normally a light blue, were darkened by oil. The only other significant occurrence was at nest 

number 10 where the female was observed to be oiled on the upper chest and neck. 

April 16, 2000 

Checked nest number two at Teague Point. Female appeared normal in coloration. Both adults at nest number four at 

Chalk Point were found to be moderately oiled and in need of cleaning. A noose carpet was place in the nest to catch the 

incubating female. She was caught and banded (788-29462) and taken to the shoreline to meet waiting cleanup team 

from TriState Bird Rescue. After the male resumed incubating duties, he was caught using the noose carpet. The male, 

which was previously banded on the Patuxent River in 1995 by Cardano, was then handed over to cleanup team. The 

nest contained three eggs. One egg was transferred to the clean up team to be placed in an incubator. The other eggs 

were placed in foster nests at Teague Point and platform nest at the West End of Rt. 231 bridge. The foster nest females 

assumed incubating duties after introducing the foster egg. 

April 17, 2000 

The adults from nest number 4 at Chalk Point were cleaned and released the following day. The incubated egg was 

placed in the nest prior to release. The female, upon release at the Chalk Point shoreline flew immediately to the nest 

with the one awaiting egg. 

April 19, 2000 

Examined adults at 13 nest sites from Benedict to Long Point. Feather coloration in all adults observed appeared normal 

except for the female at nest number 52 at Sandy Point. Eggs were not present. It appeared the nest (built on old 

pilings) had collapsed and the nest had been rebuilt. The female was moderately oiled. The male was not observed. 

Because of the absence of eggs it was decided not to capture the female. 

April 20, 2000 

The two other eggs were retrieved from the foster nests and returned to nest number four at Chalk Point. The pair 

hatched and fledged two young. 

Examined adults and nest contents at 18 nest sites from Benedict to Eagle Harbor. The female at nest number 29 on 

Channel Marker #25, north of the Rt. 231 Bridge, had a small amount of oil discoloration on the legs. The male was 

observed and appeared normal. 

Nest number six at Pylon "B" contained three darkened eggs. Both male and female were moderately oiled from legs to 

neck. Both adults were trapped using the noose carpet. The female was caught first. She was previously banded 

(608-52371). The male was caught next and banded (788-29463) before handing over to the Tri State Rescue team on 

shore. The three eggs were transferred to incubators. 
The trapped birds were cleaned and release was attempted later that evening. The female was still too wet to fly and 

ended up in the water. It had to be retrieved by release team. Both adults were kept overnight for possible released the 

following morning. 

April 21, 2000 

The three eggs were placed in the nest and the birds were released. It was observed that a new pair of birds had taken 

over the temporarily abandoned nest site. Eyewitnesses observed the birds fighting and were not sure which birds were 

driven away. But, on April 23, 2000 the banded female (608-52371) was found dead downriver near Persimmon Creek. 

 Its cause of death has not been determined as of this writing. 

May 7, 2000 

Adults and contents of 32 nests from Buzzards Island Creek northward to Eagle Harbor were checked. The new female 

was on the nest incubating at nest number five at pylon "B" at Chalk Point. There was only one egg and it was darkened 

over its entire surface. The three eggs at nest number seven on pylon "C" were darker than normal. Adults at each of 

these nests did not appear discolored by oil. Oiled sticks and twigs that were recorded at pylon "A" on April 11, 2000 

were covered up by new clean vegetation, clumps of grass, and small and large sticks. 

Nest number 29, where there was an earlier report of some oil discoloration on the female contained one egg out of three 

that was gray to muddy in color. Nest number 23, which is just east of number 29 at Buena Vista had two eggs of the 

same muddy-gray color. The osprey nest platform at the entrance of Indian Creek (nest number 27) was examined for 

the first time. Oil booms had prevented up close examination prior to this. The nest had one young, approximately two 

days old, and one grayish-brown egg. The nest contained some oiled vegetation. 

Nest number 52 at Sandy Point, had three eggs of normal coloration. The female had oil discoloration on the abdomen 

and legs. The male was normal in appearance. 

May 19, 2000 

Fifty nests were examined from Broomes Island northward to Deep Landing. Nest number 30, on Channel Marker 23 at 

Long Point was new. The birds had started nesting at the nearby nest platform but moved to the Channel Marker. The 

male was wet but appeared discolored by oil. The female was oiled on legs and belly. The nest contained three eggs that 

were darker than normal. The osprey nest platform, nest number 3 at Teague Point, was predated. On May 7th the nest 

contained two newly hatched young and one egg. On this day the nest was empty and the adults were absent. 

The new female at pylon "B", nest number 6, was still incubating. The egg was probably addled by this date but it was 

decided not to remove it so as not to disrupt the bird's attachment to the site. Nest on Channel Marker 25 contained one 

darkened egg. The female was still discolored on legs and belly. 

All other nests checked appeared normal. Ospreys added additional vegetation to nests and covered up any signs of 

oiled nesting material. Except where noted all adults appeared normal in plumage characteristics. 

May 26, 2000 

Checked 43 nests from Battle Creek to Eagle Harbor. The three eggs at nest number 30, on Channel Marker 23, were 

still unhatched and darker than normal. Female's legs and belly were whiter than seen a week earlier. 

A new nest was found at new pylon "C" at Chalk Point. It was not considered an active nest. A young pair or a 

"frustration" nest from an earlier failed attempt may have built it. 

June 8, 2000 

A total of 24 nests were examined from Long Point to Hunting Creek. Collected addled eggs from nest numbers five, 
six, and 23. Nest number six, with the new female, previously recorded with one egg, now had two. Additional 

vegetation may have covered one of the eggs during inspections. Both eggs were addled and one was removed. 

The osprey nest platform south of the entrance of Hunting Creek contained two young that were five weeks old that 

weighed 1750g and 1850g respectively. It was decided to band these birds while at the nest. 

Osprey nest number 56, in front of PEPCO's Hallowing Point Lab, was empty. It previously contained two young at 

two weeks of age. One young was found dead and partially decomposed on the sandy beach in front of the lab. 

June 29, 2000 

Forty-one nests were examined in the middle region of the Patuxent River. Thirty-two young were banded with USGS 

aluminum leg bands. Three addled eggs were collected. One from nest number 39, south of Cape St. Mary's and two 

eggs from nest number 52, at Sandy Point. One of the three eggs at Sandy Point had hatched and produced one fledgling. 
United States' Department of the Interior

U. S. GEOLOGICAL SURVEY

Biological Resourc~ Division

Forest and Rangeland Ecosystem Science Center

3200 SW Jefferson Way

Corvallis, OR 97331

October 1, 2001

Mr. Peter McGowan

U.S. Fish & Wildlife Service

Chesapeake Bay Field Office

177 Admiral Cochrane Drive

Annapolis, :rvm 21401

Dear Mr. McGowan:

I have received your Draft Final Report dated September 2001 and the associated Confidentiality

Agreement which I have signed and enclosed.

Overall) the report is an excellent document. There are a few minor details that need to be address ed

and a question about some specific observation date$. I will cover them point by point below (I have

numbered the paragraphs from 1 to 29).

para 3. Palmer (1988) is nQ! in the literature cited. Actually, the Osprey chapter was written by

Henny, so it could be cited as Henny (in Palmer 1988). The 1988 reference is Handbook of North

American Birds Vol. 4, Yale Univ. Press.

para 19. I believe it is important to know the actual date of the August 2000 survey on the PEPCO

property (this relates to the 5 nests that failed). I personally know that Chesapeake Bay Ospreys nest

earlier than those here in Oregon by a few weeks, Most (87%) young Oregon Ospreys make their

first flight between 24 July and 14 August. Some data from Chesapeake Bay WcLean 1986, M.A.

Thesis, College William mid Mary) shows that Ospreys make their IJIst flight between 30 June and

20 July. Birds regularly return to the nest for a couple weeks, but then, the nest is abandoned. My

concern about the 5 nests reported abandoned in August is that the birds may have already fledged

which becomes more likely the later the survey date in August.

para 29. The calculation of the oil-related loss of 17 Osprey young includes: (11 nests with 10

young that should have produced 18.1 young [negative 8.7 young]) and (5 nests surveyed in August

that produced 0 young that should have produced 8.5 young [negative 8.5 young]). This totals 17.2

young lost. I agree with your calculations procedure; however, if the O' young counted on PEPCO

property was based upon only one survey in middle or late August, it is likely that some young

would no longer be associated with the nest, i.e., they would have fledged. In summary, one could
+

question some of the reported loss (8.5 of the 17.2 young) unless the survey was conducted early in

August, or you have additional infonnation about the nests failing at an earlier date.

References

There are some inconsistencies in capitalization. Altdet et at. has lots of caps in the title of the paper

and no date, while words are not capped for other papers. Henny (1986) has several typos and

"haliaetus~' should not be capped. Palmer (1988) reference is omitted. Poole has typo for New

York. Postupalsky has lots of caps in title and a typo.

//

Charles J. R/""""--

Wildlife Biologist (ReseaW