This project is curretly represented by the work of the two graduated students listed below.

Effects of Food Availability on Growth and Stress in Seabirds

Suzann Speckman

Seabird distribution patterns at sea often reflect fluctuations in prey availability, as birds switch foraging areas to follow prey movements or to forage in areas of higher prey abundance. To examine how variability in food supply affects the distribution of seabirds, we conducted at-sea surveys for seabirds and contemporaneous acoustic surveys for small schooling fishes in Lower Cook Inlet from 1996-1999. Effort was focused around 3 seabird colonies, the Barren Islands (well-mixed oceanic waters), Gull Island (oceanic and estuarine waters), and Chisik and Duck islands (estuarine waters). At the regional scale (>100 km), average annual estimates of prey abundance (acoustic backscatter) were significantly higher around the Barrens and Gull Island than around Chisik. Densities of Black-legged Kittiwakes (Rissa tridactyla) and murres (Uria spp.) followed the same pattern, with average densities around both the Barrens (6.2 kittiwakes and 10.4 murres/km2, respectively) and Gull Island (5.8 and 6.0/km2) significantly higher than densities around Chisik (1.1 and 1.5/km2), a pattern not necessarily reflective of colony size. At the patch scale (1-10 km), birds consistently aggregated in areas of higher prey abundance and those hotspots persisted from year to year. However, at the colony scale (20-40 km), annual estimates of kittiwake and murre densities were not significantly correlated with annual estimates of acoustic backscatter within any colony region. We suggest that the unique oceanographic regimes surrounding each colony have such strong influences on prey abundance that interannual variability within the colony scale is slight in comparison.

Modeling the Effects of Egg-Harvesting at a Gull Colony

Stephanie Zador

Balancing conservation with cultural preservation poses a challenge for resource managers in many parts of Alaska. In Glacier Bay the process is complicated by multiple factors and influences. For the Tlingit people of southeast Alaska, South Marble Island in Glacier Bay National Park is a traditional site for harvesting eggs, primarily those of glaucous-winged gulls (Larus glaucescens). Harvesting is currently not permitted, but the National Park is considering allowing limited harvesting. The goal of this study is to provide pertinent biological information for the resource managers. The study is designed to investigate the effects of harvesting eggs at the individual and colony level. We are developing a simulation model to study the effects of varying harvest/predation rates on the re-laying sequences and subsequent hatching success of gulls at the colony level.

We investigated the physiological cost of increased reproductive investment for individual gulls during the egg-laying and incubation stages. We found that the total number of eggs laid did not affect hatching success. We tested the hypothesis that gulls that laid (females) and incubated (males and females) a second clutch would show different levels of corticosterone in their blood from gulls that kept their original clutch. Birds under physiological stress exhibit high baseline levels of corticosterone, a hormone that regulates behavior in response to stressors. However, birds can modify their behavior by suppressing their stress response, thus decreasing the amount of corticosterone released during a standardized capture period without increasing their baseline levels. In our experiment, we removed the entire clutch on the day the third egg was laid in 32 nests, forcing the breeding pairs to re-lay a clutch. We captured birds from surviving control and manipulated nests at the end of their incubation period. We found no differences in the baseline levels of corticosterone, indicating conditions were favorable for the gulls. However, females from manipulated nests had suppressed stress responses, which may have resulted from a combination of laying extra eggs and poor body condition experienced by all of the females at the end of incubation. These results suggest that gulls are adapted to variable incubation investments, but the implications of these costs as mediated through adult and chick survivorship should be studied further.