. OCS Study

MMS 96-0005

Annual Variation in Seabird Attendance and Productivity on East Amatuli Island,

. Barren Islands, Alaska: Natural and Human-Induced Effects

Final Report 1992-1994

P. Dee Boersma

Professor

Julia K. Parrish

Research Assistant Professor

Department of Zoology ,

University of Washington

Seattle, WA 98195

March 1996

1
OCS Study

MMS 96-0005

P. Dee Boersma

Professor

Julia K. Parrish

Research Assistant Professor

Annual Variation in Seabird Attendance and Productivity on East Amatuli Island,

Barren Islands, Alaska: Natural and Human-Induced Effects

Final Report 1992-1994

Department of Zoology .

University of Washington

Seattle, WA 98195

submitted to:

Minerals Management Service

. Environmnetal Studies Section

949 E. 36th Ave.

Anchorage AK 99508

March 1996

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PROJECT ORGANIZATION

Principle Investigator:

Dr. P. Dee Boersma

Professor, Zoology Department

University of Washington

Seattle, WA 98195 \

Project Manager:

Dr. Julia K. Parrish

Research Asst. Professor, Zoology Department

University of Washington

Seattle, WA 98195

Technician: .

Karen Jensen

Student Hourly Employees:

Matt Wasson . .

Jen Cesca

Trista Patterson

Johanna Salatas

Nick Stathis

Anna Stathis

Jim Walseth

Time-Lapse Camera Consultants:

.Polar Alpine Inc. .

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TABLE OF CONTENTS

Project Organization iii

Table of Contents IV

List of Figures V

List of Tables VI

Executive Summary 1

Introduction 3

Methods 6

General 6

Common Murre 7

Attendance 7

Reproductive Activity 8

Fork-tailed Storm-petrel 9

Monitoring Areas 9

Results and Discussion 11

Common Murre 11

Attendance Patterns 11

Reproductive Success 12

Fork-tailed Storm-petrel 14

Reproductive Success 14

Chick Growth 15

General Discussion 16

Acknowledgments 20

References 21

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LIST OF FIGURES

Figure 1. Map of study island.

Figure 2. Monthly sea surface temperature anomalies, 1975-1991.

Figure 3. Common Murre attendance on four multiple-count plots, 1990-1993.,

Figure 4. Common Murre breeding phenology.

Figure 5. Fork-tailed Storm-petrel nest occupancy, 1990-1994.

Figure 6. Fork-tailed Storm-petrel hatching success, 1990-1994.

Figure 7. Fork-tailed Storm-petrel fledging success, 1990-1994.

Figure 8. Fork-tailed Storm-petrel hatching success versus human disturbance.

Figure 9A-E. Fork-tailed Storm-petrel growth curves, 1990-1994.

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LIST OF TABLES

Table 1. Common Murre reproductive success, 1991, 1993, and 1994.

Table 2. Fork-tailed Storm-petrel reproductive success, 1990-1994.

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EXECUTIVE SUMMARY ..

The Barren Islands, (580 55' N, 1520 W), have the-largest seabird breeding

colonies in the North Gulf of Alaska (Bailey 1976). Because they are often abundant,

conspicuous, and relatively high on the food chain, changes in seabird population

dynamics can mirror changes in the bio-physical environment, including food supplies,

oceanographic events such as EI Nino-Southern Oscillation (ENSO), and marine

pollution such as oil spills. Not all species will react similarly to a given environmental

change; however, when several species within a single system are considered, patterns of

environmental change may emerge. Aerial and ship-based surveys have shown that the

waters surrounding the Barren Islands support a dense assemblage of foraging seabirds.

However, the islands are particularly susceptible to marine perturbations, as evidenced by

the Exxon Valdez oil spill of 1989. Some estimates of Barren Islands seabird losses

resulting from this spill (e.g. murres) range as high as 50%. From 1990 through 1994, we

monitored the population activity, diet, and reproductive success of two of the most

abundant species of seabirds in the Barren Islands: Fork-tailed Storm-petrels

(Oceanodromafurcata) and Common Murres (Uria aaIge), in order to determine the

degree to which each species responded to known changes in the environment, both

natural and human-induced. For each species, methods were developed to monitor

population activity, phenology, reproductive success, and, in the case of Fork -tailed

Storm-petrels, chick growth. For the most part, methods and censusing sites were based

on OSCEAP studies conducted by Boersma and Manuwal during the late 1970' sand

early 1980' s. Seabird population monitoring usually commenced by the beginning of

July and ended during the first week in September.

. For Common Murres, patterns of population activity were estimated by counting

murres present on four separate nesting areas (approximately 2-3% of total island

attendance), after the murres had laid eggs but before chicks had fledged. Phenology was

assessed from the timing of egg production on a 5x5m study plot on the top of Light

Rock, established in 1977, as well as 35mrn time-lapse movie cameras set up in 1991,

1993, and 1994. In addition, reproductive success was calculated for all pairs within the

camera plots which could be visually followed. From 1975 through 1979, murre

attendance estimates on East Amatuli Island ranged from a low of 19,000 to a high of

61,000. From 1990 to 1992, we counted between 31,000 and 35,000 murres in

attendance on East Amatuli Island. Attendance in three of the four census areas

increased steadily from 1990 to 1993; in total, attendance rose an estimated 18%

annually. In all years, murres nesting on Light Rock produced eggs and chicks, although

there were differences in both phenology and reproductive success. Egg laying on the 5

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by 5 m plot in 1977 and 1978 was early relative to 1979; the former years are

phenologically comparable to 1993 and 1994, while 1979 is closer to the timing of 1990.

Reproductive success of murres in the time-lapse camera plots ranged from 0.65 to 0.93

fledglings per pair over the 243 pairs followed. Although there has been some concern

. that the Exxon Valdez oil spill caused a persistent decline in the reproductive output of

the remaining East Amatuli population, we found no evidence to support or refute this

contention. However, the pre-spill data available for accurate comparison was lacking,

greatly weakening any firm conclusion about the effects of the spill.

For Fork-tailed Storm-petrels, patterns of population activity were estimated by

assessing occupancy, reproductive success, and chick growth at approximately 650

marked burrows located in six study sites (A-E, Z). Throughout the 1990's, occupancy in

marked nests has hovered between 40 and 50 percent. Hatching success and fledging

success appeared to rise throughout the 1990's to a high of nearly 70% (hatching) and

90% (fledging) in 1994. Both tissue growth rate and weight gain fluctuated throughout

the 1990's. In 1993 and 1994, it took approximately 57 days for the average chick to

grow their wings from 10% (birth) to 90% of adult wingchord length. By contrast, the

average length of time required in 1990 was 68 days, an approximately 20% difference.

Weight gain followed a similar pattern. These dramatic differences in annual growth

may reflect fledging success to some degree, but also reflect the fact that Fork -tailed

Storm-petrel growth is regulated by food supply. Changes in weight gain probably

reflect food quantity, while changes in wingchord growth rate reflect changes in food

quality. Food availability may change on an intraseasonal basis and in an unpredictable

fashion, while food quality may be changing over longer periods of time (e.g. decades).

Because seabirds can modify their behavior and foraging patterns, many species

are able to ameliorate the effects of environmental change, regardless of source (i.e.

natural or human-induced). For this reason, an understanding of natural biological

variation and what causes variation to differ in direction or degree is also needed.

Ainley, Sydeman and Norton (in press) argue that the intensity and geographical extent of

the Aleutian Low Pressure System may alter wind patterns, upwelling patterns, and

consequently affect the food supply, thereby affecting seabird reproductive and

population biology in the Farallon Islands. It is interesting to note that in years when

murre reproductive success is high in California, it is low on the Barren Islands. This

"trade-off" effect may represent evidence of alternating strengths and weaknesses in the

Alaska and California current systems, as both originate from the North Pacific Current.

However, this alternating pattern is disrupted in years when the entire Pacific basin is

affected, suggesting that major oceanographic perturbations can dwarf local

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oceanographic trends .. Thus, 1992 was a very poor reproductive year for murres in both

the Farallon Islands and the Barren Islands, presumably because of El Nino.

In contrast to most 'natural perturbations, which can have either negative or

positive impacts, most human. perturbations have negative impacts on seabirds. Oil spills

are among the most dramatic human perturbations in the marine environment. Without

long-term monitoring of specific populations, it will be impossible.to make blanket

statements about the effects of oil spills on seabird populations, relative to other mortality

agents, whether natural (e.g. ENSO, food availability, winterkill) or anthropogenic (e.g.

gillnet bycatch, direct competition with fisheries, introduced predators). The Barren

Islands data do not appear to shed light on this dilemma, in that although the Exxon

Valdez oil spill killed many thousands of seabirds, it was impossible to detect long-term

differences in response to the spill by Common Murres and Fork-tailed Storm-petrels. In

part, our inability to detect change may be a result of the paucity of information on the

non-breeding, or "at-sea" component of the Barren Islands population. Seabird,

populations may be buffered from adverse effects, both naturaland human-induced, by

their non-breeding pool. The level of resilience provided by non-breeders would thus be

affected by the frequency and magnitude of disturbance: Additional human-induced

disturbance in a system already susceptible to broad fluctuations in natural perturbation,

may deplete the built-in reserve offered by non-breeders. Whether this is true, and how

important the non-breeding pool of birds is, remains to be tested.

INTRODUCTION

, Many authors argue for the use of seabirds as indicators of the marine '

environment (Boersma 1986, Furness 1987, Furness & Barrett 1991). Because they are

often abundant, conspicuous, and relatively high on the food chain, changes in seabird

population dynamics can mirror changes in: 1.) the food supply (Piatt 1990, Springer et .

al. 1986); 2.) oceanographic events such as EI Nino-Southern Oscillation (ENSO)

(Boersma 1978, Graybill & Hodder 1985, Wilson 1991, Massey et al. 1992); and 3.)

levels of marine pollution, at the lethal (Piatt et al. 1990) as well as sublethal (Boersma

1986, Gilbertson et al. 1987) levels. It is generally accepted that not all species of

seabirds will react similarly to a single environmental change (Furness & Barrett 1991).

This is because each species has different foraging and nesting behavior, such that

varying aspects of the physical/biological environment will impinge directly on each

species' fitness. For instance,' species with greater flight range may beless susceptible to

changes in the food supply than species with limited range, because the former can adjust

for nearshore food depletion by searching over greater distances from the colony.

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Population-level measurements, such as attendance, diet, hatching success, chick growth

rate, etc. may give us an integrated, albeit selective, window on the environment.

However, when several species within a single system are considered, patterns of

environmental change may emerge. The Barren Islands, with its abundant resident

seabird colonies, provide such a system within which to quantify environmental change.

Located at the mouth of Cook Inlet, the Barren Islands, (58055' N, 1520 W), have

the largest seabird breeding colonies in the north Gulf of Alaska (Bailey 1976). East

Amatuli Island, located on the east side of the island group (Figure 1), supports a

particularly diverse assemblage of avian fauna that includes surface feeders and pursuit

divers (Bailey 1976). These islands are ideally suited for seabirds due to three

complimentary factors: First, the local topography and physical oceanography result in

upwelling with a concomitant surge in productivity. Aerial and ship-based surveys have

shown that the waters surrounding the Barren Islands support a dense assemblage of

foraging seabirds (Piatt pers. comm.). Second, the system is not only uninhabited by

man, but is protected as part of the Alaska Maritime National Wildlife Refuge

(AMNWR). Lastly, although the island system supports a small number of raptors and

river otters, predators are by-and-large absent. The latter two factors minimize

disturbance to breeding habitats. All three factors contribute to the continuing

reproductive success of the Barrens' seabirds and also highlight the importance of the

islands as a population center for seabirds in the north Gulf of Alaska. However, the

islands are particularly susceptible to marine perturbations because of their location at the

mouth of Cook Inlet. As evidenced by the Exxon Valdez oil spill, pollutants that are

introduced into Prince William Sound and the north Gulf of Alaska are likely to flow

through the Barren Islands and may linger there for several weeks because of the large

tidal exchange.

From 1990 through 1994, we monitored the population activity, diet, and

. reproductive success ·of two of the most abundant species of seabirds in the Barren

Islands: Fork-tailed Storm-petrels (Oceanodromafurcata) and,Common Murres (Uria

aalge). Prior to 1990, extensive data was collected on Fork-tailed Storm-petrels

(Boersma et al. 1980, Boersma unpub. data) and occasional data was collected on murres

(Manuwal Ivdu). These datasets have allowed determinations of the degree to which

each species responds to known changes in the environment, both natural and humaninduced. For example, Fork-tailed Storm-petrel burrow occupancy (# occupied/#

checked) and egg volumes were significantly lower in 1983 and 1984, years in which an

EI Nino-Southern Oscillation (EN SO) event was known to have affected physical

oceanography conditions in the Pacific (see chapters in Diaz & Markgraf 1992). During

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this period, sea-surface temperature (SST) anomalies i~ a four-degree sided square

surrounding the Barren Islands were often in excess of 1.0oC (Figure 2). Anomalously

high SST conditions have been associated with downturns in oceanic productivity (Sharp

1992), and thus potentially the food supply of lower food chain feeders such as Forktailed Storm-petrels (see references in Wooster & Fluharty 1985, Ainley & Boekelheide

1990). Thus, while not strictly causative, there is a definite, and biologically

interpretable, correlation between a change in the larger physical environment and the

reproductive biology of the seabird species.

Natural variation is not the only source of environmental change. Human-induced

perturbations. affect the environment on several scales. At a global level, changes such as

rising C02 emissions can affect temperature, which in turn may affect both terrestrial and

aquatic productivity (Halpert & Bell 1993). Regionally, human interaction with the

oceanic environment may have produced changes in aquatic community structure due to

fishing pressure (Springer et al. 1986). Such changes can often have far reaching effects

on the food supply, and thus abundance, of regional seabird and marine mammal species

(Springer et al. 1986).' I

Locally, point-source pollution can have a drastic effect on the marine

environment. A case in point is the Exxon Valdez oil spill of 1989.(Piatt et al. 1990).

Approximately 30,000 bird carcasses of 90 species were recovered following this spill

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(Piatt et al. 1990), and current estimates of total bird mortality have run as high as

I 500,000 (Parrish & Boersma, in press): Because over 70% of the recovered carcasses

were murres, and the Barren Islands murre colonies (located on East Amatuli and Nord

Island, respectively) comprise the largest murre colony in the path of the spill, both

assessment of the.damage to, and monitoring recovery of, the Barren Islands murre

population is of serious scientific and management interest.

While it is possible to ascribe a potential cause, such as the Exxon Valdez oil

spill,' to a measured effect, such as a decline in the murre population, in general the

pattern' of population activity and reproductive effort of each species is going to be

influenced by a complex combination offorces, both natural and anthropogenic (Hunt

'1987). It thus becomes imperative to not only monitor seabird populations, but to also

collect accurate measurements on the physicallbiological environment (Hunt 1987,

Parrish & Boersma 1995). These two pieces must then be superimposed such that

measured environmental change is applicable on a biological scale appropriate to the

species in question. In this context, scale is relevant to both time (as in the average life of

a seabird) and space (as in the foraging range of the bird). For instance, nearshore I

changes in food supply may affect thealcids, (murres and puffins), more than Fork-tailed

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Storm-petrels, because the former have a restricted foraging range around the nesting

colony. Thus, localized shortages may affect the diet, and eventually the reproductive

success, of these species. Fork-tailed Storm-petrels may be able to compensate for local

shortages by increasing search distance and time. While this may increase egg neglect

and slow chick growth, reproductive success.measured as fledglings per pair, may be

unaffected. Furthermore, species with limited foraging ranges may be more susceptible

to marine pollutants such as oil, should the oil cover a broad proportion of the species

foraging range. During the breeding season, murres and Tufted Puffins should

experience the brunt of any oiling in the Barren Islands' area, because their at-sea

distribution is limited to close to the island. Thus, there is potential for naturally-induced

downturns, such as those caused by changes in food supply, to be synergistically

exacerbated by oiling events.

Because of the islands' high vulnerability to oil spill impacts due to its geographic

location at the mouth of the Cook Inlet ( an area of shipping traffic and potential oil and

gas development), a three-year study to monitor the majormarine avifauna was funded

by the Outer Continental Shelf Environmental Assessment Program (OCSEAP) from

1977 through 1979 (ManuwaI1980). That study concentrated primarily on three species:

Fork-tailed Storm-petrels, Tufted Puffins and Common Murres. For each species,

methods were developed to monitor population activity, phenology, reproductive success,

and in some cases chick growth. From 1980 through 1984, these studies were continued

under Boersma and concentrated on the Fork-tailed Storm-petrel. Monitoring of the

Fork-tailed Storm-petrel population and, to a lesser extent, Tufted Puffins and Glaucouswinged Gulls (Larus glaucescens) was conducted intermittently from 1985-1989 by the

U.S. Fish & Wildlife Service AMNWR staff (Nishimoto et al. 1986, Nishimoto et al.

1987, Nishimoto & Beringer 1988, Nishimoto & O'Reilly 1989). In 1990, Boersma

resumed monitoring, and has continued surveying the seabird activity on East Amatuli

Island through 1994.

METHODS

General

At the beginning of each field season (late June), a crew of field technicians and

volunteers was transported from Homer to East Amatuli. As in previous years, camp was

set up in a depression in the primary dune on the east side of Amatuli Cove. In 1993 and

again in 1994, the camp was expanded to accommodate U. S. Fish & Wildlife

Servicepersonnel. Seabird population monitoring usually commenced by the beginning

of July and ended during the first week in September. In all years, camp was dismantled
by mid-September. During years in which time-lapse-movie cameras were installed on .

Light Rock, a brief dismantling trip was made in October. In 1991 and again in 1993,

data on Fork-tailed Storm-petrels was also collected during the October visit. In 1994,

three separate visits were made.toEast Amatuli, en lieu of a permanent field camp. Visit

timing and adverse weather conditions precluded collection of murre population

information. However, these data were collected by US Fish & Wildlife Service

. personnel.

Common Murre

,Attendance

From 1990 through 1992, island attendance was. estimated by counting murres

present on the island after the murres had laid eggs but before chicks had fledged (see

Wanlesset al. 1982, Hatch & Hatch 1989). Counts were made when the water around

the islandwasrelatively calm (seas less than 1 mj.andvisibility was good. All counts

were restricted to between 1100 H and 1900 H. Before ce~suses began, observers

practiced counting selected areas by making independent counts and then comparing

data. The .practice area was then censused more closely by both observers counting

together .. Independent counts were then made again. If these counts differed by more

than ten percent, the entire process was repeated until the counters agreed which birds . . ~,.,

had been missed or invented. Attendance was defined as the number of murres directly

counted on the cliffs. This figure does not take into account the percentage of the

population that was not present, (i.e, foraging). Therefore, we did not attempt to use the

attendance count to calculate the number of pairs nesting on the island. Instead,

islandwide attendance censuses were used to provide a broad-brush picture of changes in

East Amatuli colony size. In 1993, US Fish & Wildlife Service personnel assumed the

responsibility of estimating' island. murre attendance.

In addition to the island census, four areas (Oval, Swatch, and Triangle Rock NW

and S; respectively; Figure 1) were censused several times throughout the day on

different dates throughout the breeding season to provide a more in-depth dataset for the

determination of interannual trends (1990-1993). Counts were made as described above.

In 1990-1992, counts were made from beyond the kelp bed (far), at unspecified locations

affording a clear view of the area. In 1Q93, counts were made much closer from within

the kelp (near). IUs possible that closer counts could be higher because-individual birds

would be easier to spot. To test for methods effects, far and near counts were conducted

in ··1993on. the same day and compared. There were no statistical differences, indicating

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near counts did not bias attendance upwards. In 1993 and 1994, U.S. Fish & Wildlife

Service personnel also made duplicate counts of these multiple-count areas.

Reproductive Activity

During all boat surveys murre phenology was qualitatively assessed. Specifically,

we observed: 1) whether the murres were occupying breeding ledges or continuing to

raft, and 2) whether "flyoffs", defined as large numbers ofmurres (>100) flying from the

cliffs in unison, occurred. Flyoffs were taken as an indirect indication that laying had not

started in an area. We also noted whether recently laid murre eggs or freshly eaten eggs

were seen on Light Rock during occasional visits. As our field season started in early

July, it was impossible to determine when ledges were initially colonized. However, we

operationally defined the beginning of reproductive activity as the time when the majority

of the murre population was present on the breeding ledges and remained there

throughout the day (i.e. no flyoffs).

Phenology was also assessed from the timing of eg!5production on a study plot on

the top of Light Rock, established in the densest part of the colony in 1977 (Manuwal

1980). Originally 17.6 m2, the plot was expanded to 25 m2 in 1978 and located in the

same general area as in the previous year (Boersma pers. obs.). The plot was reestablished in 1990, and surveyed through 1992. As in the 1970's the plot was visited

after the initiation of egg laying (7 July and 1 August) and again after chicks started to

hatch (1 September) in order to count eggs and chicks. Visits invariably flushed the

resident adults, so an attendance count was never possible. The number of eggs and

chicks appearing on the 5 x '5 m plot was used as an indication of relative reproductive

success for the murre population. During the first two visits, all eggs within the plot were

marked such that a loss rate between visits could be calculated. This loss rate is assumed

to be the,result of disturbance, primarily created by visiting the plot. Losses occurred

because Glaucous-winged Gulls entered the plots after murres flushed, and preyed upon

some percentage of the eggs. Because of this disturbance, our measures of egg and chick

production from the 5 x 5 m plot are somewhat lower than what would actually have been

produced.

During 1991, two 35mm time-lapse movie cameras were installed on Light Rock,

one on the flat top and one on the North-sloping side. In 1993 and 1994, four such

cameras were installed (1993 - two on flat top, two on North side; 1994 - three on flat

top, one on North side). Cameras were set-up before the onset of the murre laying season

. (late June) and removed after murres had left for the season (late September - early

October). Cameras took pictures every 6 (1991) or 10 minutes (1993; 1994), from dawn
to dusk. Subplots within the frame of each camera were used to assess daily and seasonal

patterns of attendance and phenology. Reproductive success was calculated for all pairs

within the plot which could be visually followed. Pairs whose position on the camera

subplot occluded them from clear view were not followed, as it was difficult to

impossible to clearly distinguish their reproductiye output. Pair occlusion was a

particular problem in the sloping plots, which led to the reduction in sloping camera

plots from 1993 to 1994 as they were not usefulwith respect to accurate assessment of

murre reproductive success .. Although this method may be somewhat ambiguous, we had

no a priori reason to believe there was a potential correlation between proximity to:the

camera and reproductive' success.

For clearly visible pairs, all frames within each day were examined for sightings

of eggs or chicks. As murres are protective of their eggs/chicks, and the cameras were

taking "snapshots" in time (albeit tens of frames/day), there were days in which clear

.sightings for each pair's reproductive output were not possible. This was particularly tiue

during stormy weather, when picture quality was reduced.as well as during hatching

when parents remainded extremely close to new chicks. Therefore, we used a series of

conservative operational definitions, based.on range of days an egg or chick was sighted,

to catego.rize the likelihood of hatching and fleding success. For each pair, successful

fledgling production was operationally defined by one of the following: 1.) chick . - ~ '

sightings over an 18+ day period, or 2.) chick sightings and sightings of adults with

. , .

wings down (indirect evidence of chick presence) over a 20 d~y period, or 3.) chick

sightings and sightings of adults with wings down over an 18 day period combined with ._~ .

egg sightings over a 30+ day period. Chicks were defined as having probably fledged if

they were sighted directly or indirectly or less than 18 days and/or their eggs were sighted

less than 30 days. Therefore, reproductive success was defined conservatively as:

i ...! ,. • -, •

fledglings/( eggs- relays) I "

and liberally as: \.

(fledglings + probable fledglings/(eggs - relays)

.,

•. Fork-tailed Storm-petrel . \

Monitoring Areas " '

All permanently staked burrows in 6 study areas (A, B, C, D, E, and Z; Figure 1)

were examined for evidence of nesting activity at the beginning, middle, and end of each

field season. During each year, new burrows were Identified and added to the

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permanently staked list. Area checks were used to determine burrow usage and

reproductive success of a known population as follows:

occupied burrowepresence of adult, egg, or chick

burrow occupancy=occupied burrows/total burrows checked

active burrowepresence of an egg or chick

burrow activity=active burrows/total burrows checked

hatching successechicks produced/eggs

chick mortality=dead chicks/chicks produced

fledging success=chicks fledged/chicks produced

reproductive success=chicks fledged/active burrows

Because the field season ended before all chicks had actually fledged, the chick fledged

category included actual fledgers plus all chicks in healthy condition at the end of the

field season.

After the first complete area check, all active burrows were marked for the season

with surveying flags. Active burrows were then monitored at three-day intervals

throughout the nesting season as follows: Adults in the burrow were checked for band

identification. Unbanded adults were banded. Once both birds of a pair were banded,

adults were no longer removed from the burrow. If the burrow did not contain an egg or

chick, and no adult was found for three consecutive visits, then the burrow was removed

from the monitoring list. Burrow condition (dry, damp, wet; flooded) was also noted.

Eggs were removed from the burrow and measured to the nearest 0.1 mm with

vernier calipers (length and width). Until hatching, relative egg temperature was

consistently checked as a measure of incubation (warm, cool, or cold), and hatching state

was recorded (presence and number of stars and pips). Pipped eggs usually hatched

within 1-5 days. If an egg was cold for more than 6 sequential visits, it was considered

dead and the nest was removed from the monitoring list .

.Once the chick had hatched it was not removed from the burrow until the adult

was no longer present, usually 2-5 days from hatching. Chicks were aged by classifying

feather tracts on the back (small dots, large dots, lines), back skin color (red, pink,

white/grey), and tarsus color (white, grey) Chick activity was noted on each visit as

follows: responsiveness (active, lethargic, torporous), wing and feet temperature (warm,

cool, cold), down condition (dry, damp, wet). Chick weight (to the nearest g) and wing

measurements (to the nearest mm) were made on every visit. Wing chord was defined as

the distance, on an unstretched wing, from the carpal joint to end of the bone, down,

shaft, and/or feather as they appeared during chick growth. Chicks that were considered

to be near fledging (identified by the presence of fully grown flight feathers and no
down) were banded, The yearly chick growth rate was calculated by taking mean weight

and wing measurements from Day I through fledging and. performing a best-fit growthcurve regression on the points (BoersmaSc Parrish, in prep.). , ' , ,

: .' ~ . ,

RESULTS AND DISCUSSION r .

Cornmon Murre

Attendance Patterns

to.

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From 1990 to 1992, we counted between 31,000 and 35,000 murresin attendance

on East Amatuli Island (Boersma etal. 1995). In 1993, US Fish & Wildlife Service

personnel estimated the East Amatuli population at 33,000 (Roseneaupers. cornm.).

Attendance figures were unavailable for the 1994 season. -In all years the majority of the

murre population nested. on the southeast side of the main island, and secondarily on East

Amatuli Light Rock. Because whole island censuses were only made once, these figures

should not betaken as accurate representations of eitherisland attendance or population

size. Instead, these figures represent a broad estimate of annual attendance.

There has been a-large amount of controversy surrounding the degree to which the

Exxon Valdez oil spill impacted, and continues to impact, the Barren Islands murre· '

population (Boersma et al. 1995, Nysewander et al. 1993, Parrish & Boersma 1995).

Although the attendance-figures reported here can be used as broad-brush baselines for

future years, they are, unfortunately.not directly comparable to earlier census data as the

latter were estimates rather than actual counts. In addition, specific information about

counting methods, including number of observers, platform, optics, time of day and time

of season- are lacking .. From J 975. through 1979"murre attendance estimates on East

Amatuli Island ranged from a low of 19,000 to a high of 61,000 (Boersma et al. 1995) .

. Four areas: Oval, Swatch, Triangle Rock NW and S, respectively, were counted

between 2 and 10 times per season, allowing a more accurate estimation of annual

changes and variation in attendance. These four areas represent 2-3% of the .total East

Amatuli population, and are located in three separate locations along the periphery of the

,/ ". J

main island .. Attendance.in three ofthe four areas increased steadily from 1990 to 1993

(Figure 3). In total, attendance rosean estimated 118 murres per year, or approximately

18% annually (Figure 3). These high annual increases are the strongest indication that

there was a large negative impact on the pre-1990 population (presumably the Exxon

Valdez oil spill of 1989). Annual increases of +20% indicate thatfollowing theExxon

Valdez oil spill either breeding murres stayed away from the colony forseveral.years (see

-Sydernan 1993), or adults were immigrating into the Barren Islandspopulation, or some

combination of the two: However, not all colony locations experienced such dramatic

11
increases. On East Amatuli Light Rock, timelapse Camera 1 (located on the upper flat

portion of the subcolony, to the immediate Northeast of the navigation light) attendance

counts did not vary significantly (Table 1). That we did not see an island-wide pattern of

dramatic increase suggests that all parts of the island are not necessarily affected in a

similar manner by a single event such as an oil spill. Some locations on East Amatuli

may be "optimal" nesting habitat, such that vacant spaces were quickly filled by

migrating (local or regional) adults. There is some indication from long-term banded

populations that movement between colonies of reproductively active adults does occur

(Halley and Harris 1993). By 1991, the first year time-lapse camera data were collected,

"optimal" locations may have already stabilized.

While the breeding population may appear to be in recovery, the total population

(i.e. including the non-breeding component) may have sustained a serious loss. If what

we are seeing is an equilibration of the breeding population at the expense of the

/ .

"standing stock" of the non-breeding population, further perturbations could seriously

affect murre population numbers and reproductive success: Thus, we still know little

about the Exxon Valdez oil spill effect on murre population resiliency even though we

can find no evidence of massive damage, either mortality or denigrated reproductive

success, to the population.

Reproductive Success

.In all years, murres nesting on Light Rock produced eggs and chicks, although

there were differences in both phenology and reproductive success. During 1990-1992,

eggs and chicks were observed directly by field personnel visiting Light Rock. In 1991,

1993, and 1994, time-lapse 35mm movie cameras recorded the reproductive activity of

subplots of murres nesting on the flat top (l to 3 cameras/year) and sloped sides ('1 to 2

cameras/year) of the Rock. Because the latter method is remote and does not disturb the

. birds, a more accurate picture of reproductive success is possible.

For the time-lapse cameras, we defined reproductive success as a range of values

bounding the probable true value (see Table 1). The pairs we followed do not represent

100% of the birds in each camera plot, but the number of pairs for which we were able to

view eggs and/or chicks repeatedly. In the plots for which eggs, and especially chicks,

could never be seen, the number of pairs followed is much lower than the probable

number of reproductive pairs (i.e. Cameras 3 and 4). Reproductive success of followed

pairs ranged from 0.65 to 0.93 fledglings per pair over the 243 pairs followed (Table 1).

In 1993, pairs in the Camera 2 plot experienced lower reproductive success (0.58);

however, this low value was not a result of natural processes but instead stemmed from a

12
Coast Guard helicopter landing on Light Rock on August 12, 199,3which caused many

adults to temporarily desert and therefore led to the loss of eleven eggs. If these birds are

not.included in the reproductive success calculation, success increases to 0.79 fledglings

per pair. In general, once eggs had hatched, the chance of chick mortality was quite

small, even during large disturbances such a,sthat caused by the .helicopter landing in

1993. ' "

-

, In 1991, 1993, and 19,94,phenology could be.explicitly assessed on the timelapse

c:amera plots. In other ye,ars (1977-1979; 1992),!isits were made to the 5 x 5 m plot

(location of Camera 2 in .~9?3 and 1994),. and the number of eggs were counted. Thus, it

is possible to assess whether egg presence is consistent with phenology patterns on the

camera plots.or whether .phenology was earlier in non-timelapse years. It is difficult to

.t - ,; •

determine whetherphenology was ever Iater, as lower egg values might be due to either

later laying, lower,overall production,or both. Because visits to the 5 x 5 m plot

disturbed the murres, there was. associated egg,loss, .primarily due to predation by

Glaucous-winged Gulls. Although there was,re-alying, eg~ predation undoubtedly

decreased production, making absolute comparisons with time-lapse camera data , ,

inappropriate.,

There are two evident phenological patterns. Within ~ year, laying was not

necessarily synchronous across Light Rock, although it appeared to be synchronous

within each camera plot. In 1993, murres nesting on the flat top of the rock laid 6 days

e~lier than murres nesting along sideledges. Between years phenology also changed

(Figure 4). From 19Q1 on, lay date appears togetprogressively earlier, although this

pattern is somewhat confounded by 1992 (Figure 4). There have been claims that murre

phenology following the Exxon Valdez oil spill has been significantly later than in ,'

previous years. It appears that egg laying on the 5 x 5 m plot in 1977 and 1978 was early

relative to 1979, and that egg production in~977 was.very high. Visual inspection,

indicates that 1978 is phenologically comparable to 1993 and 1994, while 1979 is closer

, ,

.to 1990 (Figure 4). Acknowledgingthat these data areseverely limited, wefind no

consistent pre-post spill pattern ..~ t •

- .

•" Although there has been some concern that the Exxon Valdez oil spill caused a

persistent decline in the reproductive output of the remaining East Amatuli population,

we found n<?evidence to support this contention. In reality, pre-spill reproductive data do

not provide an accuratepicture ,of reproductive success, as the only available data come

from visits to the 5 x 5m:plot {Boersma et aI. J995). If the post-spill population was

indeed severely hampered in egg and chick production, we would have expected that

reproductive success in, 1991 would have .been low relative to other closelymonitored .' . ~ '

13
populations in Alaska. In fact, this is not the case. It is possible that the birds nesting on

Light Rock occupy the most optimal habitat and, as such, experienced little of the postspill repercussions ascribed to other sectors of the Barren Islands murre population. In

1993 and 1994, the U.S. Fish & Wildlife Service personnel collected data on reproductive

success of pairs nesting on the East Amatuli headland immediately east of Light Rock.

Fork-tailed Storm-petrel

Reproductive Success

Throughout the 1990's, occupancy in marked nests has hovered between 40 and

50 percent (Figure 5, Table 2). Although occupancy in 1991 appears to drop, it is

actually higher than calculated because unfound nests (i.e. previously marked nests which

remained un-located through the season presumably because the stake disappeared; NNF)

and collapsed nests (nest collapse occurred over the winter; COLL.) were not recorded,

erroneously inflating the number of available but unoccupied nests: Hatching success

(chicks/eggs) and fledging success (fledgings + healthy end-of-season chicks/hatchlings)

of both marked and new nests appeared to rise throughout the 1990's (Figures 6 & 7).

This pattern may be an artifact of a change in methods from 1990-1993 to 1994. During

1994, nests were only checked intermittently (2-3 times per trip), as opposed to a regular

three-day schedule in prior years. The number of nest checks prior to mean hatch date

for the colony within year is negatively correlated with hatching success in a stepwise

fashion (Figure 8). In other words, five or fewer nest checks result in lower

abandonment, and thus higher hatching success. Therefore, the higher hatching and

potential fledging success in 1994 could be parti~lly the result of lowered disturbance

levels. For nests checked on a regular basis (i.e. 1990-1994), experienced adults from

marked burrows appeared more likely to desert (as measured by relative hatching

success) than unbanded adults from nests which were newly found that year (i.e. birds

inexperienced with humans). It is unclear what is determining this behavioral pattern in

the adults. However, once chicks had hatched, nest status (marked or new), as well as

number of times nests were checked prior to fledging, appeared to have little influence on

fledging success.

The negative correlation between nest-check frequency and hatching success,

combined with the counter-intuitive difference in hatching success between old (marked)

and new nests, suggests that long-term monitoring projects need to seriously consider

researcher effects. Chronic trampling of the vegetation results in soil compaction and

gulley formation. Eventually, this erosional process may decrease the inherent worth of

14
nearby nests, forcing the residents to find new nest sites. Therefore, long-term

.monitoring programs need to first assess what level of reproductive information is

n~cessary relative to the expected reproductive impairment of the population as a result

of collecting those data. We suggest a hierarchical approach: I.) long-term marked nests

should be used for chick growth studies as the latter does not appear to be affected by

human disturbance and 2.) new nests in similar habitat to the marked nests should be used

~.

to determine annual reproductive success. Ideally, the nests used for reproductive

success should be checked intermittently, 2-3 times early in the season to assess

occupancy and forecast mean hatch, 3-4 times around mean hatch, and 2-4 times late in

the season just prior to fledging. ; ,.~

•r .

Chick Growth,-, ' ,..

Both tissue growth rate and weight gain fluctuated throughout the 1990's (Figures

9A-E). In 1993 and 1994, it took approximately 57 days for the average chickto grow

. their wings from JO% (birth) to 90% of adult wingchord lengthtfull.adult wingchord

length was setat 162 mm). By contrast, the average length oftime required in 1990 was

68 days, an approximately 20% difference. Weight gain followed a similar pattern: at 70

days the average chick weighed 96 grams in '1994 and only 75 grams in 1990. These

dramatic differences in annual growth may reflect fledging success to some degree, as a

higher percentage of chicks fledged in faster growth, 'heavier years (i.e. 1994).

Boersma and Parrish (in prep.) hypothesize that the.demonstrable changes in

mean annual growth rate reflect the fact that Fork-tailed Storm-petrel growth is primarily

externally regulated by food supply. 'Changes in.weight gain probably reflect food

quantity, while changes in wingchord growth rate reflect changes in food quality. Thus it

is possible to havehigh availability of low quality prey (i.e. high lipid, low protein

producing fat chicks with slow wing growth), as may have been the case in the 1990' s.

Conversely, it is also possible to have high availability of high quality food ,(i.e. high

protein leading to fast. wing growth) as was seen in the 1980' s. This challenges the idea

that seabird growth, particularly in the storm-petrels, is regulated by bottlenecks.in

anatomical development (Ricklefs 1979). Changes in both wing growth patterns and

weight gain are likely the synergistic result of changing food availability as well as

changing food quality. Food availability may change, on an intraseasonal basis and in an

unpredictable fashion .. Food quality may be changing over longer periods oftime (e.g.

decades) as a result of sever~ potentially interacting events: decadal shifts inoceanic

warming (Royer 1989); chaotic disturbance such as El Nino-Southern Oscillation, shifts

, ,

15
in trophic structure as a result of long-term fishing pressure (Springer et al. 1986), and

short-term shifts in trophic structure caused by oil pollution.

General Discussion

Determining how perturbations affect seabird biology is particularly difficult

because both natural and human induced changes are occurring continuously.

Furthermore, the strength and direction of natural perturbations are both variable and

chaotic. However, if we can use these "natural experiments" as indicators of how the

changing environmental conditions will impact seabirds, we will perhaps be able to

forecast how additional human-induced changes will alter seabird population biology.

Because seabirds can modify their behavior and foraging patterns, many species

are able to ameliorate the effects of environmental change. For this reason, it is difficult

to use seabirds as indicators of environmental change without extensive information on

their biology. An understanding of natural biological variation and what causes variation

to differ in direction or degree is also needed (Wiens 1995).

Physical oceanography is largely driven by climatic changes. Intensity of

upwelling and sea-surface temperature eireknown to be linked to some seabird

demographic parameters (Boersma 1978). There is increasing evidence that seabirds are

sensitive to changes in these physical variables. Population changes of seabirds in the

Fro-allons appear to track temporal variation in some large-scale oceanic conditions

(Ainley and Lewis 1974). Ainley, Sydeman and Norton (in press) argue that the intensity

and geographical extent of the Aleutian Low Pressure System may alter wind patterns,

upwelling patterns, and consequently affect the food supply, thereby affecting seabird

reproductive and population biology in the Farallon Islands, For example, breeding of

Common Murres in the Farallon Islands has become earlier and is correlated with an

increase in sea-surface temperature along the coast of California from the 1970' s through

the 1990's (Sydeman and Ainley 1994). Both the Common Murre and Cassin's Auklet

(Ptychoramphus aleuticus) delayed reproduction in the Farallon Islands in 1982-1983 and

1992-1993, apparently in response to EI Nifio. Apparently, higher productivity is

associated with earlier egg laying dates in murres (Sydeman and Ainley 1994).

Interestingly, only two species of seabirds on the Farallon Islands, both storm-petrels,

appeared to show little response to annual variability in marine productivity.

Our data from the Barren Islands characterizes a very different system, but a

strikingly similar pattern. Royer (1989) reports that the Gulf of Alaska has been warming

since the mid-1970's. In general, warmer waters are associated' with lower productivity.

The negative trend in the onset of egg laying (i.e. delayed) in the Barren Islands murre

16
_ ... _,

. population is correlated with a generaLincr.ease in se~ surface temperature in the north

Gulf of Alaska. , ", " .

.One of the most striking aspects of this comparison is the apparent dovetail effect

of north versus south. For instance, egg laying of murres on East Amatuli Island

appeared to be earlier in 1977 and 1978 and later in 1979., The opposite pattern is shown

by murres on the Farallon Islands which laid later in 1977 and 1978 than they did in

1979. Egg layingin 1979 and 1991 appeared to be e~li.er than normal in the Farallon

Islands but later than normalin the Barren Islands. This .opposition may represent

evidence of alternating strengths and weaknesses in the Alaska and California current

systems, as both originate from the North Pacific Current. However, this alternating

pattern is disrupted.in ye~s when the, entire Pacific basin is affected, such as an ENSO

year, suggesting that majoroceanographic perturbations can dwarf local oceanographic

trends. 'rhus, 1992 was a veryl poor reproductive ye':lf for murres in both the Farallon

Islands and the Barren.Islands, presumably because of El Niiio."

Fork-tailed Storm-petrel data from the Barren Islands are consistent with the

...•., '.-

interpretation that major oceanographic changes are.occurring in the north Gulf of

Alaska. Generally, growth rates of storm-petrel chicks have been slower in the 1990' s

than in the mid-1970's and early 19~9' s, suggesting that food availability and/or quality

has changed. This is perhaps a surprising result given that of the 12 species of breeding

birds on the Farallon Islands, only 2 species showed little response to annual variability:

Fork-tailed and Leach's sto~~petrels; ..

In contrast to most natural perturbations, which can have either negative or

. - -/

positive impacts, most human perturbations have negative impacts on seabirds. Oil.spills

are among the most dramatic humanperturbations in the marine environment. However,

the relative importance of massive vers~s chronic oil spills in structuring seabird breeding

populations is unclear; Oil spills oftenresult in aspike in adult seabird mortality; ,

however, the long-term effects on seabird populations are not known. Some researchers

, I • ,~. • "'"

have pointed out that although oil spills undoubtedly kill thousands of seabirds, average

winterkill can reduce a population by 5-20% each year (Dunnet 1982, Clark 1984), * . ~ f· ' •

leading one to the conclusion that oilspills are aminor component of seabird mortality.

However, other authors have pointed out that winterkill disproportionately removes

young-of-the-year and juvenile birds, while oil spills can principally affect br~eders,

particularly if the spill occurs close to breeding colonies during the breeding season (Piatt

etal..1991). In sum, without long-term monitoring of specific populations, it will be

impossible to make blanket statements about the effects of oil spills on seabird

populations, relative to other mortality.agents, whether natural (e.g. ENSO, food

"_'.:.-

17 '
availability, winterkill) or anthropogenic (e.g. gill net bycatch, direct competition with

fisheries, introduced predators).

The Barren Islands data do not appear to shed light on this dilemma, in that

although the Exxon Valdez oil spill killed many thousands of seabirds, it was impossible

to detect long-term differences in response to the spill by Common Murres and Forktailed Storm-petrels. The impact on these two species was expected to differ, as large

numbers of murres were killed by the oil and apparently few Fork-tailed Storm-petrels

were killed by the oil (Piatt et al. 1990).

Since we first began working in the Barren Islands in 1976, use of the waters

around the islands and of the islands themselves has increased dramatically due to

increased boat traffic, fishing, scientific visits, and tourism (Boersma pers. obs.).

Distinguishing the negative effects on area seabirds of these increasing human uses of the

area from impacts associated with oil development and transport in the Cook Inlet area

would be difficult. When coupled with natural perturbations and long-term

oceanographic trends, teasing out cause-and-effect becomes impossible without a solid,

long-term database designed to detect subtle changes in population parameters on a broad

scale.

18

With the effects of several scales of perturbations occurring why haven't there

been more obvious changes in seabird populations in the Barren Islands? The answer to

this question lies in seabird breeding biology. Seabirds are long-lived and hence changes

in reproductive success may not be apparent for a decade or more. Many species have

the ability to switch food sources should conditions change, a further buffer against

environmental variability. Changes in the level of adult mortality are expected to

produce long-term effects in population structure and reproductive function. Why then

did we see few changes, other than direct mortality, from the Exxon Valdez oil spill? The

answer may be in the non-breeding component of seabird populations. We know almost

nothing about this component of the population: how big it is, its age structure, and its

geographic range. Seabird populations may be buffered from adverse effects, both

natural and human-induced, by their non-breeding pool. The level of resilience provided

by non-breeders would thus be affected by the frequency and magnitude of disturbance.

Additional human-induced disturbance in a system already susceptible to broad

fluctuations in natural perturbation may deplete the built-in reserve offered by nonbreeders. 'Whether this is true, and how important the non-breeding pool of birds is,

remains to be tested.

The Exxon Valdez oil spill demonstrated that the Barren Islands are likely to be

an important reference site. The location of the Barren Islands and extreme tidal
1----

I

\

exchange that characterizes the area make them ideal for examining the effects of both

natural and anthropogenic disturbance on seabird populations. Some baseline

information is available and patterns of change can be detected. Reference areas will

become increasingly important in determining both short and long-term environmental

change. However, routine monitoring without scientific innovation will not be adequate

for the challenge, because refinements in datacollectiori must be made over time in order

to test relevant, time-sensitive hypotheses. For instance, it is clear from our study and

others (e.g. Hatch and Hatch 1989) that single, yearly censuses can only provide a broad

estimate of population size, rather than a specific statistically robust number. However,

the effort required to collect statistically adequate data at the level of entire colonies may

be economically unfeasible in the long-term. Therefore, we recommend the adoption of

methods, such as 'our timelapse camera system (allowing.extremely accurate data

collection on a small part of the colony), which speak to both long-term monitoring and

statistical robustness; both are needed should future injury and damage assessment be

necessary.

. '

, '.

. '

r' .' ~

,

..

i'\

" F;' ., '

\. '"

"

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. ',,' • •

,\

19
20

ACKNOWLEDGMENTS

We would like to thank the Alaska National Maritime Refuge for allowing access to East

Amatuli and East Amatuli Light Rock. Maritime Helicopters and Homer Ocean Charters

provided much needed logistics and comfort. Bill St. Lawrence of Polar Alpine was an

essential component of the time-lapse camera crew. This study would not have been

possible without the dedicated efforts of many students, volunteers, and technicians,

particularly Sonia deBary and Arthur Kettle who worked on.the project during 1990-

1991. Partial funding for the time-lapse camera work was provided by Exxon USA. This

study was funded in part by the .u. S. Department of the Interior (USDOI), Minerals

Management Service (MMS), through Intra-agency Agreement No. 14-35-0001-30670

with the USDOI as part of the MMS Environmental Studies Program.
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\ i

, .

~_.... "I

i..' rt".

23
Camera- Year Reproductive

Success

Table 1 - Reproductive success for all pairs of Common Murres that could be followed

within each time-lapse camera plot, East Amatuli Light Rock, Barren Islands, Alaska.

C1 - 1991

C1 - 1993

C2 - 1993

C3 - 1993

C4 - 1993

C1 - 1994

C2 - 1994

Attendance

(X + SD)

57 ± 5.1

57 ± 9.6

58 ±3.0

35 ±5.0

62 ± 7.9

52±3.7

59 ± 5.1

Number of

e s

46

41

44

19

24

39

41

Number of

rela s

Number 'of

chicks

0.74-0.76

0.76-0.89

0.58-0.79

0.79-0.89

0.65-0.83

0.90-0.92

0.93

4

1

4

34

34

24

17

19

36

38

1

o

1
I

• I
1992

STATUS AREA TOTAL NNF COLL. OCe. ACTIVE CHICKS FLEDGED

OLD

A 1806 72 68 28 18

B 5424 33 33 149

C 29

0

7 12 11

5

2

D 215 271 97 97 54 29

E 177 287 74 74 32 14

Z 3743 16 16 113

NEW

A 108732

B1

110

0

C00000

D 107

7

5

3

E

8

443

1

Z

111

1

0

1993

STATUS AREA TOTAL NNF COLL. ace. ACTIVE CHICKS FLEDGED

OLD

A 188 18

2 70 67 29 21

B 5405 28 23

85

C 290

0 1093

2

D 230 24

4 105 99 34 23

E 196 33

6 60 56 28 15

Z 373

0 17 165

4

NEW

A1

1111

B1

111

1

C00

000

D1

1000

E 29 29 28 12

8

Z00

0

0

0
1994

STATUS AREA TOTAL NNF 'CaLL. OCC. ACTIVE CHICKS FLEDGED

OLD A 176 8 8 68 63 48 45

B 56 0 7 24 20 16 15

C 29 0 2 10 8 6 5

0 209 7 2 86 79 58 57

E 200 6 1 83 74 57 51

Z 34 0 2 10 8 6 6

NEW A 6 6 5 4 4

B 3 3 3 ,2 ,2

C 0 0 0 0 ,0

D 12 12 10 9 9

E 28 28 25 17 17

Z 2 '2 2 1 'I

,

,

, ,
--- ------

East Amatuli Island, Barren Islands, Aaska

Swatch

¥

I,)

J ••••• ll"I~~r' Light Rock

5 mile

Figure 1. Topographic map of East Amatuli Island, Barren Islands, Alaska, showing the placement of six Fork-tailed Storm-petrel study

areas with permanently marked burrows (A, B, C, D, E, Z), the Conunon Murre census areas (Oval, Swatch, Triangle Rock), and Light

Rock - the site of Conunon Murre reproductive success assessment (5x5m plot; 35mm time-lapse camera plots). Inset is location of East

Amatuli relative to the Barren Islands system.
1

1

-L '

1

1

1

1975 76 77 . 78

1

1

·1

79 1980 81 82 83 84 85 86 81 88 -·89 1990 91

year

Figure S. Sea surface temper~ture anomaly, by month, integrated over a 2° square centered on the Barren Islands (1975-1991).

Temperatures greater or less than 1° are shown by open circles. All data from COADS.
T. Rock NW (+O/year; R2 = 0.00)

o Oval (+43/year; R2 = 0.92)

~ 250

~

Swatch (+29/year; R2 = 0.93)

T. Rock S (+46/year; R2 = 0.84)

200

QJ be

C! 150

QJ

~

100

1990 1991 1992 1993

Year

648 811 818 1036 Total Attendance

25% 1% 27% 3-year average = 17.7%

Figure 3. The average annual attendance of Common Murres at four multiple-count areas (Oval, Swatch, Triangle Rock South and

Northwest, respectively). Lines are least-squares fit. Slopes are indicated as the average gain in attendance per year. R2 values indicate

slope fit. Total attendance summed over all four areas, and the corresponding percentage increase is indicated below each year. Percent

increase is calculated as (l-(larger value/smaller value» to correct for polarization.

~------------------
300 tm-Si5 300 199ft-~x5

250 2SO

200 200

'" '" ~ 150 8 ISO

L<I

100 100

SO so

0

0

300

250

200

'"8 150

Ul

100

50

. 0

i978 ·5x5

. '\

300

250

200

'"~ 150

100

• so

o -f--r-r-1I""'T-r"'"T-"'-r-'l~-r--,.-,

300

250

'200

~ 150

- -100

50

o -f-,.-••••. -.--T--r- .•.•...•...•..•.•.. -r-T--I

1991·5 x 5

• 300 1992 • 5 :Ii:5 ;.

250

200

100 1991-TLC

g'" ISO

L<I

100

so

o-t-"'-r-'l-r-r--r-"'-r-'l-r-r"~

100 1993·TLC

__ 80

60

.% 40

-,

80

60

%

40

20

100 1994-TLC

20

JULIAN DAY'

80

60

%

40

.~

Figure 4. Phenology in Julian days, as assessed by the number or percentage of eggs laid, of Common Murres nesting on East Amatuli

Light Rock from 1977 to 1994. 5x5 - the original plot set up by Manuwal and Boersma, which was visited 1-3 times each year (data are

actual number of eggs on the plot); TLC - time-lapse camera #1 plot located above and west of 5x5 plot (data are percent of total eggs

laid). A zero (0) indicates a visit was made but no eggs were present. TLC data are cut off when all eggs are laid (i.e. 100% is reached).
.-tI'J ..•..

tI'J

~

=:

"0-

~

~_.

c:-

a

•.•..

60

50

-

545 598

639

661

.

583

.

40

30

20

10

o

Q .-4 N M ~

c::l\ c::l\ c::l\ c::l\ Q\

c::l\ c::l\ c::l\ c::l\ c::l\ .-4. ~ .-4 .-4 .-4

Year

Figure 5. Nest occupancy in permanently marked burrows of Fork-tailed Storm-petrels,

1990-1994.
•

M

80

Marked Nests lI')

0 New Nests M

.-

~

Q

-- M

60

(/}

(/}

~

C.J

C.J .00

::. ,

00 40

; 00.

etl. =:

.-.:

C.J

••• 20 =

==

Figure 6. Hatching success of Fork-tailed Storm-petrels, 1990-1994. Permanently

marked nests are filled bars, new nests, by year, are open bars. Numbers above each bar

are sample sizes.
~ ~

•

Marked Nests ~

100

D New Nests

..-

80 ~

~

-.-

rn

rn

~ ..

C.J 60 M

C.J

::

CI)

0.0 40

~

..-0.0

"0

~

- 20 ~

0

= ~ N ~ ~

Q'\ Q'\ Q'\ Q'\ Q'\

Q'\ Q'\ Q'\ 0\ Q'\

-

_.

~ - - Year

Figure 7. <Hedging success of Fork-tailed Storm-petrels, 1990-1994. Permanently marked

nests are filled bars, new nests, by year, are open bars. Numbers above each bar are

sample sizes.
=,

~. ~

~~ 10

Q

20

1991

•

1993

.' 8

... . ,

i

'1992. 1982

•0

00

o

,

0.2 0.4

Hatching

0.6

Success

.' Marked Nests

o ! New Nests

1980

o •

·'1981

O.

1994

, I

o 4, --~- __ ---r-------,r--- --,-----r-----,

0.0 0.8 .

Figure 8. Hatching success of Fork-tailed Storm-petrels as a function of the average

number of nest checks before mean hatch date, by year. Permanently marked nests are

filled circles, new nests, by year, are open circles. Numbers .above each filled circle are

years. '
I

~

165 1990

132

...

...

e 99 ,

~

,

s

,. 68 , til

'E ~

~

66

,

0 ,.

48 OQ .c

u ,

Qll ,

.,

c: , ••a ~ 33 ,

Z8

e,

,

e

e 111 ZII 8 311 4. 511 68 7'

Age (days)

1991

165 lee 165 1993

I

I •

13Z

Ie 13Z

I

I

I

8' I

99

6. 8' 99

!

!. ~.

.11I s

-

011

:r

'E 66

48 ::; 'E 66 4. -

o·

;0 0

0;

.c:

'5 ;,

u

tlO ..

a

l>D c::

c:: ~

33

ze e,

~

33 ze ~

•

lit ZII 311 48 511 68

ZII 311 4' 58 61 71 I Age (days) Aile (days)

I

I 165 1992

100 165 1994

I

132 80 I

132 I

I

I

I

I

8' I

99 69

~ 8' 99

~

I !.

III !. - ~. I

'E 66

40 ;:r 'E 66 0

;0 .8

;;

.c:

~ .. l;l.

;r- •• I

c::

B c::

B

~ 33 Z0 ~ j 33 e,

I

I

1'1 2'1 3'1 4'1 se 68 111 ZII 3. 48 511 61 Age (days)

Age (days)

I

I

I

Figure 9 A-E. Wingchord growth (solid line) and weight gain (dashed line), averaged

I within age (in days) for Fork-tailed Storm-petrel chicks, 1990 _ 1994.