colonization, population growth, and nesting success

The Condor 106:791–800 q The Cooper Ornithological Society 2004

COLONIZATION, POPULATION GROWTH, AND NESTING SUCCESS OF BLACK OYSTERCATCHERS FOLLOWING A SEISMIC UPLIFT VERENA A. GILL1,3, SCOTT A. HATCH1

AND

RICHARD B. LANCTOT2

1

U.S. Geological Survey, Biological Resources Division, Alaska Science Center, 1011 East Tudor Road, MS 701, Anchorage, AK 99503 2U.S. Fish and Wildlife Service, Migratory Bird Management, 1011 East Tudor Road, MS 201, Anchorage, AK 99503 Abstract. We present data on the colonization of Middleton Island, Alaska, by Black Oystercatchers (Haematopus bachmani) following the creation of an extensive rocky intertidal zone after the Alaskan earthquake of 1964. The first pair of oystercatchers was detected in 1976, and it was another 5 years before the population increased to three pairs. Oystercatcher numbers increased steadily thereafter, with a population explosion occurring in the 1990s. By 2002, there were 171 territorial pairs on the island. The total number of birds increased from two in 1976 to 718 in 2002. Breeding-pair densities on Middleton Island are the highest recorded for any portion of Alaska, averaging more than 5 pairs per km of shoreline in 2002. Nesting success in 2001 and 2002 was greater (83% or more of the eggs laid hatched) than that reported for any other population of oystercatchers in Alaska or along the Pacific Coast. We attribute this exponential growth rate and exceptionally high reproductive success to the large area of available and suitable habitat, the low number of avian predators and the complete lack of mammalian predators, low rate of nest loss to high tides and storm surges, and a low level of human disturbance. We propose nominating Middleton Island as a regional Western Hemisphere Shorebird Reserve Network site because a high percentage of the world’s and region’s population of Black Oystercatchers resides there during the breeding season. Further, since Middleton Island may be the single most important site in Alaska for Black Oystercatchers, we suggest it be protected from future development. Key words: Alaska, Black Oystercatcher, colonization, earthquake, Haematopus bachmani, nesting success, population ecology.

Colonizacioń, Crecimiento Poblacional y E´xito de Nidada de Ostreros Negros Luego de un Movimiento Sı´smico Resumen. Presentamos datos sobre la colonizacioń de la Isla Middleton, Alaska, por el Haematopus bachmani, luego de la creacioń de una extensa zona intermareal rocosa como resultado del terremoto ocurrido en 1964. La primera pareja de ostreros fue detectada en 1976, y pasaron otros 5 anõs antes de que la poblacioń aumente a tres parejas. Desde entonces los nu´meros de ostreros crecieron constantemente con una explosioń de la poblacioń ocurrida en los 1990s. En 2002 habıá 171 parejas territoriales en la isla. El nu´mero total de individuos aumento´ de dos en 1976 a 718 en 2002. Las densidades de parejas reproductivas en la Isla Middleton son las ma´s altas registradas en cualquier lugar de Alaska, promediando ma´s de 5 parejas por km de costa en 2002. El e´xito de nidada en 2001 y 2002 fue mayor (83% o ma´s de los huevos depositados eclosionaron) que el informado para cualquier otra poblacioń de ostreros de Alaska o de la costa Pacı´fica. Atribuimos esta tasa de crecimiento exponencial y el excepcional y alto e´xito reproductivo, a la gran superficie con ha´bitat adecuado disponible, al bajo nu´mero de aves predadoras y a la completa ausencia de mamı´feros predadores, a la baja tasa de perdida de nidos por mareas altas u oleaje por tormentas, y al bajo grado de disturbio humano. Proponemos la nominacioń de la Isla de Middleton como Sitio Regional de la Red Hemisfe´rica de Reservas para Aves Playeras, dado el elevado porcentaje de la poblacioń mundial y regional de ostreros negros que allı´ residen durante la temporada reproductiva. Adema´s, dado que la Isla Middleton podrıá ser el sitio ma´s importante de Alaska para Haematopus bachmani, sugerimos que deberıá ser protegida del desarrollo en el futuro.

Manuscript received 30 December 2003; accepted 27 April 2004. 3 Present address: U.S. Fish and Wildlife Service, Marine Mammals Management, 1011 East Tudor Road, MS 341, Anchorage, AK 99503. E-mail: [email protected] [791]

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INTRODUCTION Over the last 30 years the majority of studies on Black Oystercatchers (Haematopus bachmani) have been conducted in British Columbia (Hartwick 1974, 1976, 1978, Butler and Kirbyson 1979, Hartwick and Blaylock 1979, Groves 1984, Purdy and Miller 1988, Hazlitt and Butler 2001, Hazlitt 2002), with a few in Washington (Nysewander 1977), California (Legg 1954, Morrell et al. 1979, Lindberg et al. 1987), and Baja California (Kenyon 1949, Jehl 1985). However, more than 50% of the world’s estimated 11 000 Black Oystercatchers breed in Alaska and about 30% of those reside within the Kodiak Archipelago and south-central region of the state (e.g., Prince William Sound; Andres and Falxa 1995). However, studies on oystercatchers in Alaska have been more limited and have focused on evaluating the effects of the 1989 Exxon Valdez oil spill (Andres 1997, 1999, Murphy and Mabee 2000) and introduced foxes (Byrd et al. 1997), quantifying habitat use (Byrd et al. 1997, Andres 1998), and more recently, on evaluating possible impacts from human activities (J. Morse, pers. comm.). Two additional studies have focused on general breeding ecology in Alaska, both at small colonies in the southeastern portion of the state (Webster 1941a, 1941b, 1942, Lentfer and Maier 1995). With a small population size and vulnerability to disturbance, Black Oystercatchers are a species of concern (Alaska Shorebird Working Group 2000, Brown et al. 2001). The Black Oystercatcher is one of the principal indicator species of nearshore ecosystem health in Alaska (USDA Forest Service 2002) and is an apex predator along the North Pacific shoreline (Marsh 1986, Hahn and Denny 1989, Falxa 1992). These factors make gathering baseline data important for understanding the effects of natural and anthropogenic environmental perturbations on the birds and the intertidal community they inhabit. We studied Black Oystercatchers on Middleton Island (Fig. 1), an isolated island in Alaska that harbors a sizable portion of the Alaskan population and that differs from other portions of the species’ breeding range in that it has newly created habitat, is relatively free of predators, and has low levels of human disturbance. Despite being gregarious and highly conspicuous, Black Oystercatchers were not observed

FIGURE 1. of Alaska.

Location of Middleton Island in the Gulf

on Middleton Island prior to the great Alaskan earthquake of 1964 (Ridgway 1893, Parker 1923, Rausch 1958, O’Farrell and Sheets 1962) nor in the succeeding decade (Sowls et al. 1978). The island had little, if any, suitable habitat prior to the earthquake as the shoreline consisted only of steep cliffs and a small beach that was submerged at high tide (Fig. 2). The 1964 earthquake, measuring 9.2 on the Richter scale, uplifted the island as much as 4 m (Grantz et al. 1964, Plafker 1966, Hanna 1967, Hastie and Savage 1970). This created an extensive, flat, and marshy lowland area and intertidal zone that now surrounds the entire island (Fig. 2). This rocky intertidal zone resembles, but is much broader and more continuous than, the tidal flats that are distributed unevenly along the coastline of south-central Alaska. Middleton also differs from other islands in that it is far from the mainland (120 km), hampering colonization by many avian and mammalian species that prey on Black Oystercatcher eggs and young in other portions of the species’ range (Andres and Falxa 1995, Byrd et al. 1997). In addition, oystercatchers on Middleton are not exposed to the same level of disturbance from human activities as oystercatchers in nearby Prince William Sound or Kenai Fjords National Park. Black Oystercatchers frequently either fail to nest or abandon nests as a result of human intrusion (Ainley and Lewis 1974, Warheit et al. 1984, Andres and Falxa 1995).

COLONIZATION BY OYSTERCATCHERS AFTER A SEISMIC UPLIFT

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FIGURE 2. Shoreline of Middleton Island, Alaska, before and after the 1964 earthquake, illustrating habitat changes due to seismic uplift and succession. (A) 1949, (B) 1978, (C) 2000. Photographs by Don Miller (A) and Scott Hatch (B, C).

In this study, we documented the colonization, population growth, and nesting success of Black Oystercatchers residing on Middleton Island, Alaska, following the seismic uplift in 1964. First, we present data from a series of population surveys conducted between 1976 and 2002 and discuss how overall population size and the numbers of territorial pairs and nonbreeders have varied over time. Second, we compare nesting success from 2001 and 2002. Finally, we compare our findings with other studies and discuss factors that may explain the unusual population growth and nesting success of Black Oystercatchers on Middleton Island. METHODS Fieldwork was conducted on Middleton Island (508269N, 1468209W), which is located about

105 km south of the entrance to Prince William Sound and 120 km from the Alaska mainland in the north-central Gulf of Alaska (Fig. 1). Middleton is an unforested island with an abundance of low-sloping or level gravel beaches and a rocky intertidal zone. Uplift from the 1964 earthquake created about 405 ha of new supratidal land. The island currently comprises about 1295 ha, is 2 3 8 km in size, and has approximately 33 km of shoreline. The mean tide level is 1.7 m, with a maximum tidal range of 5.4 m (NOAA 2003). Changes in the topography of the island following the 1964 earthquake have had a remarkable effect on bird populations. Cliff-nesting seabirds have declined, partially because former sea-cliff faces have eroded over the years and are now mostly vegetated. In contrast, waterfowl

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and Glaucous-winged Gulls (Larus glaucescens) have proliferated (Gill and Hatch 2002) because much of the uplifted land has become an extensive wetland. Besides Glaucous-winged Gulls, which prey on oystercatcher eggs and young (Andres and Falxa 1995), Middleton Island has few avian predators. Several pairs of Bald Eagles (Haliaeetus leucocephalus) and one or two Peregrine Falcons (Falco peregrinus) frequent the island in summer. There are no mammalian predators of Black Oystercatchers (see Andres and Falxa 1995) on Middleton, and no people permanently reside on the island. The Federal Aviation Administration and U.S. Geological Survey maintain a few part-time personnel, and waterfowl hunters occasionally visit during the fall, but rarely visit the shorelines occupied by Black Oystercatchers. FIELD METHODS

To assess the initiation and growth of the Black Oystercatcher population on Middleton Island, biologists conducted 10 islandwide surveys between 1976 and 2002. Surveys consisted of counting birds while walking around the entire perimeter of the island. Observers walked along the high-tide line, which provided a good view of foraging, roosting, and nesting habitats commonly used by Black Oystercatchers (Andres and Falxa 1995). Surveys were conducted over several days each year by 1–3 people and occurred during incubation or early chick rearing when adults actively defended their territories. Only territorial pairs were counted prior to 1994, whereas later counts included territorial and nonterritorial individuals. Territorial pairs are easily distinguished from nonbreeding birds because they defend well-defined feeding and nesting territories, using a loud communicative display called ‘‘piping’’ and extended aerial pursuits (Andres and Falxa 1995). Nonbreeding birds typically roost and forage communally, while territory-holding birds usually roost singly and forage within their territories (Andres and Falxa 1995). The density of breeding oystercatchers was determined by dividing contemporary shoreline length by the number of territorial pairs. Shoreline length was estimated using an Alvint Dual-Faced Map Measurer (Bloomfield, Connecticut) on the most recently available aerial photograph of Middleton Island.

FIGURE 3. Location of Black Oystercatcher nests (n 5 61; unfilled circles) found on Middleton Island, Alaska, in 2002. This was not a complete survey of the entire island. The solid line depicts the shoreline of Middleton Island prior to the 1964 earthquake, which created a large intertidal zone. The dotted line approximates the current shoreline. Nest locations for 2001 are not illustrated because GPS coordinates were not available.

To obtain baseline data on the breeding performance of Black Oystercatchers, a subsample of nests were monitored in 2001 and 2002. Unlike the islandwide population counts, we only monitored a portion of the coastline to assess nesting success. The south and southeastern portions of the island were not searched at all, and other smaller areas were also excluded due to personnel limitations (Fig. 3). However, the nests we monitored were a representative subsample of all oystercatcher nests on the island both in terms of habitat quality (uniform, flat intertidal area around most of the island), predation pressure (Glaucous-winged Gulls nest consistently along the entire length of the island) and human disturbance. Nests were marked by flagging an object near the nest in both years. In 2002, we also used a GPS receiver to map and relocate active nests (Fig. 3). To estimate hatch-


ing date, all eggs within each nest were floated upon their initial discovery. Location within the water column and angle were used as indicators of incubation stage (Westerskov 1950, van Passen et al. 1984). To calibrate the projected hatching date, eggs from most nests were floated at least twice and some eggs were floated three times. All nests were visited on the expected date of hatching and every 4–5 days thereafter. Nests were also checked opportunistically when biologists passed through territories during other activities. We assumed a chick hatched 3 days after an egg starred and one day after it pipped (Andres and Falxa 1995). Hatching success was based on observations of chicks or hatched shell remains in the nest bowl or of chicks within a territory. If all eggs within a nest disappeared, we searched for evidence of predation or saltwater inundation. Because Black Oystercatchers raise their broods entirely within their territories (Andres and Falxa 1995), we assumed chicks found inside a territory indicated successful hatching by the resident pair. STATISTICAL ANALYSES

We used polynomial regression to model the population growth of Black Oystercatchers on Middleton, adding terms based on significance values and the distribution of residuals. Total counts were log-transformed to meet the assumptions of normality. For 2001–2002, we calculated average clutch size and hatching success (per egg and per nest), brood size at hatching, and mean dates of laying and hatching. Laying date was defined as the date on which the first egg was present in a nest and was usually determined by back-calculating from observed hatching using a 26-day incubation period (Andres and Falxa 1995). In seven cases, laying date was determined from the stage of incubation indicated by flotation. Hatching dates denoted the appearance of the first chick of a brood. We tested all components of nesting success for interannual differences. Nonparametric tests were used when a variable did not meet the assumption of normality or homogeneity of variances. Laying and hatching dates were tested using a t-test. Clutch size and brood size at hatching were tested with the Mann-Whitney U-test, and remaining contrasts were tested with Pearson chi-square. Rejection levels were set at P 5 0.05 (two-tailed tests), and values are reported as means 6 SE.

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FIGURE 4. Population trend of Black Oystercatchers on Middleton Island, Alaska, 1976–2002. Filled squares represent the total number of birds, filled circles the number of territorial birds, and unfilled circles the number of nonterritorial birds. Prior to 1994, only the number of territorial birds was recorded. Total number of birds is best explained by the equation: log (n) 5 0.218(year) 2 430.30 (r2 5 0.91, P , 0.001).

RESULTS COLONIZATION AND POPULATION GROWTH

The increase of Black Oystercatchers following their colonization of Middleton Island was exponential (Fig. 4). Oystercatchers were not observed on the island prior to or during a 1956 survey (Rausch 1958), and only one pair was present when the next survey was conducted in 1976. After 1976, five years passed before the population increased to three pairs, and growth continued to be slow through the 1980s. The number of oystercatchers increased rapidly in the 1990s and into the 2000s. In 2002, there were 718 birds, including 171 territorial pairs, on the island. As the population increased, so did the density of territorial pairs, from 0.03 territorial pairs per km of shoreline in 1976 to 5.2 pairs per km in 2002 (Fig. 5). The proportion of territorial to nonterritorial birds in the population increased from 1994 to 1999 (from 44% to 53%) but appeared to stabilize thereafter (Fig. 4). NESTING SUCCESS

Limited searches located 41 and 61 Black Oystercatcher nests in 2001 and 2002, respectively. However, only 39 nests were included in the 2001 analysis because two of the nests found were never flagged and could not be relocated. Almost all of the nests were found in the area attributable to the 1964 uplift and all were located above the current high-tide line (Fig. 3).

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tial clutch sizes. Eggs were lost from inviability (nine of 10 eggs lost in 2001, and six of 26 eggs in 2002), suspected predation (one in 2001, and 18 in 2002), and inundation (two in 2002). DISCUSSION

FIGURE 5. Number of Black Oystercatcher territorial pairs per km of shoreline on Middleton Island, Alaska, 1976–2002.

There was no statistical difference in either laying or hatching date between years. The mean date of clutch initiation occurred on 19 May (61.1 days, n 5 34) and 16 May (60.8 day, n 5 60) in 2001 and 2002, respectively. The mean date of hatching was 13 June (60.9 day, n 5 33) and 12 June (60.9 day, n 5 50) in 2001 and 2002, respectively. There were also no detectable differences in the nesting success of Black Oystercatchers breeding on Middleton in 2001 and 2002 (Table 1). Clutch sizes were also comparable between the two years. The maximum clutch size was four eggs (one pair) in 2001 and five eggs in 2002 (one pair). Minimum clutch size was one egg in both years. Hatching success was high in both years; 83–90% of all eggs laid hatched and only 7–8% of breeding pairs failed to hatch any eggs (Table 1). The low rate of egg loss meant that brood sizes at hatching were similar to ini-

After the 1964 seismic uplift created suitable new habitat for Black Oystercatchers on Middleton Island, there was a slow colonization followed by exponential growth. This is consistent with the idea that the environment on the island was initially unfavorable but that improving habitat conditions, along with a large and flat intertidal zone, low levels of predation, and little human disturbance, ultimately favored high reproductive success and population growth for the species. Middleton Island now has all the requisite conditions for optimal Black Oystercatcher habitat but is much larger than the norm (Andres 1998, Hazlitt et al. 2002). COLONIZATION AND POPULATION GROWTH

It is unlikely that oystercatchers colonized the island much before 1976 because a gravelly or rocky intertidal zone was either lacking (pre1964) or was not yet well established (post1964). Once a mature intertidal community had been established, extensive unoccupied shoreline on Middleton Island provided ample space within which individuals could establish territories. The rapid increase in oystercatchers during the 1990s may be partially a result of the high levels of nesting success. However, Hazlitt and Gaston (2002), studying Black Oystercatchers in British Columbia, reported that only 5%

TABLE 1. Components of nesting success for Black Oystercatchers on Middleton Island, Alaska, 2001–2002. Hatching success was calculated by dividing the number of eggs hatched by the number of eggs laid; pairs were considered successful if they hatched at least one chick. Sample sizes refer to number of nests for all parameters except hatching success (where n 5 number of eggs laid). 2001 Parameter

Clutch size Brood size at hatching Hatching success (%) Pair success (%)

2002

Mean 6 SE

n

6 6 6 6

39 36 99 39

2.5 2.5 90 92

0.1 0.1 0.03 0.04

Mean 6 SE

n

Means from other studies

6 6 6 6

61 50 154 54

2.0–2.7a 0.5–1.4b 34–71c 23–71d

2.8 2.6 83 93

0.1 0.1 0.03 0.04

a Groves 1984, L’Hyver and Miller 1991, Andres and Falxa 1995, Lentfer and Maier 1995, Andres 1997, 1999, Murphy and Mabee 2000. b Vermeer, Morgan, and Smith 1992, Lentfer and Maier 1995. c Webster 1941b, Nysewander 1977, Vermeer, Ewins, et al. 1992, Lentfer and Maier 1995, Andres 1999. d Groves 1984, Vermeer, Ewins, et al. 1992, Vermeer, Morgan, and Smith 1992, Andres 1997, Murphy and Mabee 2000.


of juveniles returned to their natal area to breed. Prospecting birds from Prince William Sound or the Kenai Peninsula might also have immigrated into the Middleton Island population. Black Oystercatchers have been known to prospect up to 350 km from their nearest breeding areas (Eley 1976). The large proportion of nonterritorial birds, which differs markedly from Prince William Sound (B. Andres, pers. comm.) but is similar to fox-free islands off the Alaska Peninsula (Byrd et al. 1997), suggests Middleton Island may be important as a nonbreeding staging area during the summer. These nonterritorial birds may eventually disperse to breed in other regions of south-central Alaska or recruit into the breeding population on Middleton Island. It is possible that the population size of Black Oystercatchers on Middleton Island may eventually stabilize through increased predation by Glaucous-winged Gulls. Elsewhere, the nesting population of oystercatchers has declined in the presence of a large and expanding gull colony (Vermeer, Morgan, and Smith 1992). This has not been the case on Middleton Island, where both gull and oystercatcher populations increased sharply through the mid-1990s. However, it is possible that gulls will turn their attention to oystercatcher young as a source of food as cliff-nesting seabirds, a main staple for the gulls, continue to decline through loss of habitat from continued succession following the 1964 earthquake. The rate at which Black Oystercatcher numbers grew on Middleton Island (especially in the 1990s) far surpasses that of any previously published account for the species (Ainley and Lewis 1974, Nysewander 1977, Byrd et al. 1997). Today, Middleton Island has one of the highest densities of oystercatchers within Alaska (Andres and Falxa 1995). The average of 5 pairs per km of shoreline we recorded in 2002 surpasses the density of birds reported for mainland southcentral Alaska (#0.6 pair km21; Andres and Falxa 1995, Andres 1998, 1999) and fox-free islands off of the Alaska Peninsula (#2.5 pairs km21; Byrd et al. 1997) and the Aleutian Archipelago (#2.4 pairs km21; VAG, unpubl. data). The highest densities of nesting oystercatcher pairs in Prince William Sound are on islands with recently created habitat: glacial moraines or, like Middleton Island, beaches uplifted by the 1964 earthquake (B. Andres, pers. comm.). In southeast Alaska, record high densities (11–54

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nests km21) were reported for the Beardslee Islands (Glacier Bay National Park), but nearby forested islands averaged only 1.4 nests km21 (Lentfer and Maier 1995). Much like Middleton Island, Glacier Bay offers prime new habitats for oystercatchers owing to recent glacial retreat. However, these record-high densities were on islands orders of magnitude smaller than Middleton Island. More recent observations in the Beardslees suggest much lower numbers (,1 pair km21, M. Romano, pers. comm.), leaving Middleton Island as perhaps the single most important locality for breeding oystercatchers in Alaska. The current density of oystercatchers on Middleton Island falls in the middle range of those reported for lower latitudes along the Pacific Coast (Nysewander 1977, Vermeer, Ewins, et al. 1992, Vermeer, Morgan, and Smith 1992). However, all of the locations that documented higher Black Oystercatcher densities than Middleton Island were much smaller islands. NESTING SUCCESS

The nesting success of Black Oystercatchers on Middleton Island surpasses other published accounts in terms of hatching success, the number of pairs that hatched at least one young, and brood size at hatching. Laying and hatching dates, and clutch size were similar to those reported from other areas (Table 1). The extremely high hatching success of Black Oystercatchers on Middleton Island is likely the result of several factors. First, there are no mammalian and few avian predators. The lack of predation by Glaucous-winged Gulls is surprising and the reasons for it unclear. On Cleland Island in British Columbia, increases in Glaucouswinged Gull numbers were correlated with declining numbers of breeding oystercatchers (Vermeer, Morgan, and Smith 1992). On Middleton Island, the gulls appear to focus their activity on the colonial seabirds and geese. In addition, there is a large population of introduced rabbits, which the gulls prey on extensively (Roberts 1985). Second, the intertidal zone and all of the beaches on Middleton Island slope gradually. Broad, gradual beaches allow oystercatchers to nest well above the water line, resulting in relatively few nests being lost to flooding, a factor that accounts for up to 10% of nest failures in other places (Andres and Falxa 1995). In addition, this habitat feature has been linked to better

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hatching success for Black Oystercatchers because of the potential for higher chick provisioning rates on a flatter territory (Hazlitt et al. 2002). Finally, there is little direct or indirect human disturbance on Middleton. In other regions, this has resulted in large population declines (Warheit et al. 1984, Andres and Falxa 1995). Because Middleton Island differs in several respects from other localities inhabited by Black Oystercatchers, we cannot be sure which of the above factors is most responsible for the exceptional nesting success. Low predation is a strong candidate, however, as prior studies suggest that nest predation is the dominant factor influencing nesting success in oystercatchers (Andres and Falxa 1995). MANAGEMENT RECOMMENDATIONS

The 2002 population surveys suggest that about 7% of the world’s and 36–48% of south-central Alaska’s oystercatcher population resides on Middleton Island during the summer months. It is unknown if they winter there, although oystercatchers are present from at least early April (VAG, pers. obs.) to early October (D. Gibson, pers. comm.). The summer population alone qualifies the island for inclusion in the Western Hemisphere Shorebird Reserve Network as a regional site because it supports at least 5% of the world population (Western Hemisphere Shorebird Reserve Network 2004). Andres and Falxa (1995) suggested areas hosting high densities of Black Oystercatchers be protected from development and any associated disturbance. Large portions of the island are currently owned by Chugach Alaska Corporation and MIDICO, both for-profit organizations with options to pursue activities that could impact oystercatchers. Transfer of these properties to public ownership or incorporation of vulnerable areas into a longterm environmental trust through a partnership with the private landowners would ensure that untoward future developments do not occur. ACKNOWLEDGMENTS The Alaska Science Center of the U.S. Geological Survey, and the Migratory Bird Management and Marine Mammal Management Offices of the U.S. Fish and Wildlife Service funded this project. We thank Naomi Bargmann, Christy Hand, and Steven Hornstein for assistance in the field in 2001 and 2002. D. A. Frazer, P. Gould, M. Howe, D. Nysewander, and A. E. Zabloudil conducted counts for the U.S. Fish and Wildlife Ser-

vice in the 1970s and 1980s. We appreciate the help from numerous volunteers who helped count oystercatchers during the 1990s. Personnel of the Federal Aviation Administration stationed on Middleton Island provided access to much-appreciated shower and laundry facilities. We especially thank Jim Simpkins who went out of his way to help us. We thank Daniel Blanco of Wetlands International, Argentina, for translating the abstract into Spanish. David Dobkin, Jud Monroe, and two anonymous reviewers provided helpful comments that substantially improved this manuscript.

LITERATURE CITED AINLEY, D. G., AND T. J. LEWIS. 1974. The history of Farallon Island marine bird populations, 1854– 1972. Condor 76:432–446. ALASKA SHOREBIRD WORKING GROUP. 2000. A conservation plan for Alaska shorebirds. USDI Fish and Wildlife Service, Migratory Bird Management Office, Anchorage, AK. ANDRES, B. A. 1997. The Exxon Valdez oil spill disrupted the breeding of Black Oystercatchers. Journal of Wildlife Management 61:1322–1328. ANDRES, B. A. 1998. Shoreline habitat use of Black Oystercatchers breeding in Prince William Sound, Alaska. Journal of Field Ornithology 69:626–634. ANDRES, B. A. 1999. Effects of persistent shoreline oil on breeding success and chick growth in Black Oystercatchers. Auk 116:640–650. ANDRES, B. A., AND G. A. FALXA. 1995. Black Oystercatcher (Haematopus bachmani). In A. Poole and F. Gill [EDS.], The birds of North America, No. 155. The Academy of Natural Sciences, Philadelphia, PA, and The American Ornithologists’ Union, Washington, DC. BROWN, S., C. HICKEY, B. HARRINGTON, AND R. GILL. 2001. The U.S. Shorebird Conservation Plan. 2nd ed. Manomet Center for Conservation Sciences, Manomet, MA. BUTLER, R. W., AND J. W. KIRBYSON. 1979. Oyster predation by the Black Oystercatcher in British Columbia. Condor 81:433–435. BYRD, G. V., E. P. BAILEY, AND W. STAHL. 1997. Restoration of island populations of Black Oystercatchers and Pigeon Guillemots by removing introduced foxes. Colonial Waterbirds 20:253–260. ELEY, T. J. 1976. Extension of the breeding range of the Black Oystercatcher in Alaska. Condor 78: 115. FALXA, G. A. 1992. Prey choice and habitat use by foraging Black Oystercatchers: interactions between prey quality, habitat availability, and age of birds. Ph.D. dissertation, University of California, Davis, CA. GILL, V. A., AND S. A. HATCH. 2002. Components of productivity in Black-legged Kittiwakes Rissa tridactyla: response to supplemental feeding. Journal of Avian Biology 33:113–126. GRANTZ, A., G. PLAFKER, AND R. KACHADOORIAN. 1964. Alaska’s Good Friday earthquake March 27, 1964; a preliminary geologic evaluation. U.S. Geological Survey Circular 491, Government Printing Office, Washington, DC.


GROVES, S. 1984. Chick growth, sibling rivalry, and chick production in American Black Oystercatchers. Auk 101:525–531. HAHN, T., AND M. DENNY. 1989. Tenacity-mediated selective predation by oystercatchers on intertidal limpets and its role in maintaining habitat partitioning by Collisella scabra and Lottia digitalis. Marine Ecology Progress Series 53:1–10. HANNA, G. D. 1967. The great Alaska earthquake of 1964. Pacific Discovery 20:25–30. HARTWICK, E. B. 1974. Breeding ecology of the Black Oystercatcher (Haematopus bachmani Audubon). Syesis 7:83–92. HARTWICK, E. B. 1976. Foraging strategy of the Black Oystercatcher (Haematopus bachmani Audubon). Canadian Journal of Zoology 54:142–155. HARTWICK, E. B. 1978. The use of feeding areas outside of the territory of breeding Black Oystercatchers. Wilson Bulletin 90:650–652. HARTWICK, E. B., AND W. BLAYLOCK. 1979. Winter ecology of a Black Oystercatcher population. Studies in Avian Biology 2:207–215. HASTIE, L. M., AND J. C. SAVAGE. 1970. A dislocation model for the 1964 Alaska earthquake. Bulletin of the Seismological Society of America 60:1389– 1392. HAZLITT, S. L. 2002. Territory quality and reproductive success of Black Oystercatchers in British Columbia. Wilson Bulletin 113:404–409. HAZLITT, S. L., AND R. W. BUTLER. 2001. Site fidelity and reproductive success of Black Oystercatchers in British Columbia. Waterbirds 24:203–207. HAZLITT, S. L., AND A. J. GASTON. 2002. Black Oystercatcher natal philopatry in the Queen Charlotte Islands, British Columbia. Wilson Bulletin 114: 520–522. HAZLITT, S. L., R. C. YDENBERG, AND D. B. LANK. 2002. Territory structure, parental provisioning, and chick growth in the American Black Oystercatcher Haematopus bachmani. Ardea 90:219– 227. JEHL, J. R. 1985. Hybridization and evolution of oystercatchers on the Pacific coast of Baja California. Ornithological Monographs 36:484–504. KENYON, K. W. 1949. Observations on behavior and populations of oyster-catchers in lower California. Condor 51:193–199. LEGG, K. 1954. Nesting and feeding of the Black Oyster-Catcher near Monterey, California. Condor 56: 359–360. LENTFER, H. P., AND A. F. MAIER. 1995. Breeding ecology of the Black Oystercatcher in the Beardslee Island region of Glacier Bay National Park, p. 267–269. In D. R. Engstrom [ED.], Proceedings of the Third Glacier Bay Science Symposium 1993. National Park Service, Anchorage, AK. L’HYVER, M. A., AND E. H. MILLER. 1991. Geographic and local variation in nesting phenology and clutch size of the Black Oystercatcher. Condor 93: 892–903. LINDBERG, D. R., K. I. WARHEIT, AND J. A. ESTES. 1987. Prey preference and seasonal predation by Oystercatchers on limpets at San Nichols Island,

799

California, USA. Marine Ecology Progress Series 39:105–113. MARSH, C. P. 1986. Rocky intertidal community organization: the impact of avian predators on mussel recruitment. Ecology 67:771–786. MORRELL, S. H., H. R. HUBER, T. J. LEWIS, AND D. G. AINLEY. 1979. Feeding ecology of Black Oystercatchers on South Farallon Island, California. Studies in Avian Biology 2:185–186. MURPHY, S. M., AND T. J. MABEE. 2000. Status of Black Oystercatchers in Prince William Sound nine years after the Exxon Valdez oil spill. Waterbirds 23:204–213. NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION [ONLINE]. 2003. Tidal station locations and ranges. http://co-ops.nos.noaa.gov/tides03/tab2wc2b.html (10 November 2003). NYSEWANDER, D. R. 1977. Reproductive success of the Black Oystercatcher in Washington state. M.Sc. thesis, University of Washington, Seattle, WA. O’FARRELL, T. P., AND A. M. SHEETS. 1962. Birds observed wintering on Middleton Island, Alaska. Condor 64:440–441. PARKER, M. P. 1923. Northern Crusoe’s Island: life on a fox farm off the coast of Alaska. National Geographic 44:313–326. PLAFKER, G. 1966. Holocene (Recent) vertical displacements in coastal south central Alaska: a possible approach to prediction, p. 29–31. Proceedings of the second United States–Japan conference on research related to earthquake prediction problems. Lamont Geological Laboratory, Palisades, New York. PURDY, M. A., AND E. H. MILLER. 1988. Time budget and parental behavior of breeding American Black Oystercatchers (Haematopus bachmani) in British Columbia. Canadian Journal of Zoology 60:1742– 1751. RAUSCH, R. 1958. The occurrence and distribution of birds on Middleton Island, Alaska. Condor 60: 227–242. RIDGWAY, R. 1893. Scientific results of exploration by the U.S. Fish Commission Steamer Albatross. Proceedings of the United States National Museum XVI:960, Washington, DC. ROBERTS, B. 1985. Glaucous-winged Gulls prey on feral rabbits on Middleton Island, Alaska. Murrelet 66:24. SOWLS, A. L., S. A. HATCH, AND C. J. LENSINK. 1978. Catalog of Alaskan seabird colonies. USDI Fish and Wildlife Service Biological Services Program, FWS/OBS-78/78. Washington, DC. USDA FOREST SERVICE. 2002. Chugach National Forest revised land and resource management plan. USDA Forest Service Alaska Region R10-MB480c, Anchorage, AK. VAN PASSEN, A. G., D. H. VELDMAN, AND A. J. BEINTEMA. 1984. A simple device for determination of incubation stages in eggs. Wildfowl 35:173–178. VERMEER, K., P. J. EWINS, K. H. MORGAN, AND G. E. J. SMITH. 1992. Population and nesting habitat of American Black Oystercatchers on the west coast of Vancouver Island, p. 65–70. In K. Vermeer and R. W. Butler [EDS.], The ecology and status of

800

VERENA A. GILL

ET AL.

marine and shoreline birds on the west coast of Vancouver Island. Canadian Wildlife Service Occasional Paper 75, Ottawa, ON, Canada. VERMEER, K., K. H. MORGAN, AND G. E. J. SMITH. 1992. Black Oystercatcher habitat selection, reproductive success, and their relationship with Glaucous-winged Gulls. Colonial Waterbirds 15: 14–23. WARHEIT, K. I., D. R. LINDBERG, AND R. J. BOEKELHEIDE. 1984. Pinniped disturbance lowers reproductive success of Black Oystercatchers Haematopus bachmani (Aves). Marine Ecology Progress Series 17:101–104.

WEBSTER, J. D. 1941a. The breeding biology of the Black Oystercatcher. Wilson Bulletin 53:141–156. WEBSTER, J. D. 1941b. Feeding habits of the Black Oystercatcher. Condor 43:175–180. WEBSTER, J. D. 1942. Notes on the growth and plumages of the Black Oystercatcher. Condor 44:205– 213. WESTERN HEMISPHERE SHOREBIRD RESERVE NETWORK [ONLINE]. 2004. What is WHSRN? http://www. manomet.org/WHSRN/what.htm (7 June 2004). WESTERSKOV, K. 1950. Methods for determining the age of game bird eggs. Journal of Wildlife Management 14:56–67.