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U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2007–5278

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Introduction

Glacier Bay National Park and Preserve in southeastern Alaska contains a diverse assemblage of marine birds that use the area for nesting, foraging, wintering, and molting. The abundance and diversity of marine bird species in Glacier Bay are unmatched in the region, owing in part to the geomorphic and successional characteristics that result in a wide array of habitat types (Drew and others, 2007). The marine bird community includes several species that nest along shorelines on the ground, either solitarily, or in small colonies. The shorelines used for nesting by these birds generally are beaches and river outwashes. Shorelines in Glacier Bay are complex, with geophysical attributes ranging from steep bedrock cliffs to vast sand and silt tide flats. Cobble and boulder outwashes are common where drainages meet the shore, whereas braided sandy channels characterize many of the glacial outwashes. The abundant pebble beaches are used for landing kayaks—a common means of visiting the backcountry, and for camping. Marine bird nests along the shoreline are susceptible to human disturbance because they are highly dispersed and cryptic and therefore not easily detected.

Ground-nesting marine birds are vulnerable to human disturbance where visitors can access nest sites during the breeding season. Human disturbance of nest sites can be significant because intense parental care is required for egg and hatchling survival, and repeated disturbance can result in reduced productivity or total abandonment (Leseberg and others, 2000). Temporary nest desertion by breeding birds in disturbed areas has been shown to increase predation on eggs and hatchlings (Bolduc and Guillemette, 2003). Human disturbance of ground-nesting birds also may affect incubation schedules and adult foraging success, which in turn can reduce breeding success (Verhulst and others, 2001). Human activity can result in colony failure when disturbance prevents the initiation of nesting (Hatch, 2002). However, it has been argued that although some levels of human disturbance may cause a temporary change in behavior or physiology of birds (for example, walking away from the nest and returning, or raising the heart rate for a short time), these types of disturbance may not adversely affect breeding success (Nisbet, 2000).

Most of the shoreline within Glacier Bay proper is open to camping use; however, some critical wildlife areas have been closed to camping, foot traffic, and vessel approach because they contain large numbers of nesting marine birds. Data collected from individuals with back-country permits indicated visitor use at individual beaches from 1996 to 2002 varied between 1 and 416 overnight camping uses (National Park Service, unpub. data, 2004). Wildlife closures have been established at some seabird colonies, and approach within 100 m is restricted at most sites.

Previous studies of ground-nesting marine birds in Glacier Bay focused on localized populations, such as those found on single islands in wildlife closures. Patten (1974) found that Glaucous-winged Gulls (Larus glaucescens) on North Marble Island began laying eggs in mid- to late May and that intermittent interruption of incubation (about once every 4 days) did not have an adverse effect on hatching. Nelson and Lehnhausen (1983) documented 23 nesting colonies in Glacier Bay and found unusually high breeding concentrations of Arctic Terns (Sterna paradisaea), Black Oystercatchers (Haematopus bachmani), and Mew Gulls (Larus canus) compared to the rest of southeastern Alaska. The breeding ecology of Black Oystercatchers in the Beardslee Islands region of the lower bay was studied in 1989 (Lentfer and Maier, 1995). Fifty-nine nests were found in the study area and the average clutch size was 2.66 eggs. Densities of breeding Black Oystercatchers were higher on sparsely vegetated islands and reefs than on forested islands. Glaucous-winged Gull nesting activity at South Marble Island was documented in 1999 and 2000 to assess the effects of egg collection by Alaska Native peoples on breeding success (Zador and Piatt, 1999; Zador and others, 2006). In June 1999, the minimum breeding population was 570 birds and 285 active nests were found on South Marble Island. Results from the study led researchers to recommend a conservative approach to egg harvest that limited the time period, the number of collections, and the proportion of nests available for harvest.

Because of park management concerns about the nesting birds’ susceptibility to disturbance from human activities, the U.S. Geological Survey (USGS), in cooperation with the National Park Service (NPS), Glacier Bay National Park and Preserve, studied the bay-wide distribution of ground-nesting marine birds in Glacier Bay. This report summarizes results obtained during a 3-year study to measure the distribution and abundance of ground-nesting marine birds in Glacier Bay and to examine the potential for human disturbance of those nesting birds. This study provides the park with a broad assessment of ground-nesting marine-bird breeding sites in Glacier Bay, including a geographic information system database containing the location and status of all known and likely nest sites discovered during the course of this study.

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