abstracts of oral and poster presentations - Pacific Seabird Group

IS THERE A BIMODAL FORAGING PATTERN FOR LITTLE GULLS IN NORTH AMERICA
Richard Joos* 1 (r.joos@utoronto.ca) and Chip Weseloh 2 ; 1 University of Toronto, Toronto, ON CANADA;
2 Canadian Wildlife Service, Downsview, ON CANADA
The Little Gull (Larus minutus) is one of the most poorly known colonial waterbirds in North America.
Our recent work to rediscover the nesting grounds in the subarctic, outline the migratory patterns through the
lower Great Lakes, and estimate the North American population has led to several research questions. One of
the most pressing biological issues is that almost nothing is known about the foraging ecology of this rare larid
in the Western Hemisphere. This paper presents a test of the bimodal-foraging hypothesis. We conducted
behavioral observations of over 25% of the estimated population in locations from the subarctic (summer) to the
Niagara River (overwintering), and from Lake Ontario (spring migration) to Lake Erie (fall migration). The
data suggest that Little Gulls shift foraging strategies, from piscivorous in the winter to insectivorous in the
summer and during migration; that the timing and principal route of spring migration correlate with the
emergence of mayflies, Ephemerata spp., a species that also becomes a principal prey item in the subarctic; and
that foraging patterns, as well as prey shifts, are mechanisms to avoid harassment and competition from its
principal sympatric congener, Bonaparte’s Gull (Larus philadelphia). To our knowledge, this is the first study
to examine Little Gull foraging patterns in North America.
SEASONAL CHANGES IN FOOD HABITS OF SEABIRDS IN THE NORTH WATER POLYNYA: A
MULTIPLE-INDICATOR APPROACH USING DIETARY, STABLE-ISOTOPE, AND FATTY-ACID
ANALYSES
Nina J. Karnovsky 1 (nina.karnovsky@pomona.edu), Keith A. Hobson 2 , Sara Iverson 3 , George L. Hunt, Jr. 4 , and
Larry B. Spear 5 ; 1 Department of Biology, Pomona College, Pomona, CA USA; 2 Prairie and Northern Wildlife
Research Center, Canadian Wildlife Service, Saskatoon, SK CANADA; 3 Department of Biology, Dalhousie
University, Halifax, NS CANADA; 4 Department of Ecology and Evolutionary Biology, University of
California, Irvine, CA USA; 5 H.T. Harvey and Associates, San Jose, CA USA
Each year, millions of seabirds migrate to the North Water Polynya in Northern Baffin Bay to feed in its
productive waters during the six months the polynya is free of ice. This study evaluates seasonal shifts in diets
of Dovekies (Alle alle), Thick-billed Murres (Uria lomvia), and Black-legged Kittiwakes (Rissa tridactyla).
Assessment of diets was done through a combination of stable-isotope analysis of muscle and liver tissue, fattyacid
analysis of subcutaneous fat, and stomach-content analysis. Dovekies had the lowest δ 15 N values and,
hence, the lowest trophic level in spring and summer, corresponding to their consumption of herbivorous
copepods. In fall, their δ 15 N values dramatically increased as they switched to feeding on carnivorous
amphipods and fish. Throughout the study period, kittiwakes and murres had diets and stable-isotope values
similar to fall Dovekies. Fatty acids from Black-legged Kittiwakes feeding in fall were distinct, likely due to
their reliance on the pteropod Limacina limacina. Our study highlights the utility of using simultaneously
conventional diet, stable-isotope, and fatty-acid analyses to infer dietary patterns.
AT-SEA DISTRIBUTION OF XANTUS’S MURRELETS AROUND SANTA BARBARA ISLAND, 1975–
1977 [Poster]
Nina J. Karnovsky 1 (nina.karnovsky@pomona.edu), George L. Hunt 2 , Jr., and Robert L. Pitman 3 ; 1 Department
of Biology, Pomona College, Pomona, CA USA; 2 Department of Ecology and Evolutionary Biology, University
of California, Irvine, CA USA; 3 Ecology Program, NOAA/NMFS Southwest Fisheries Science Center, La Jolla,
CA USA
At-sea surveys for Xantus’s Murrelets (Synthliboramphus hypoleucus) were conducted in the waters
surrounding Santa Barbara Island, Channel Islands, during 1975–1977. In 1975, non-standardized surveys were
conducted during April–July. In 1976 and 1977, seven radial transects out to 18.5 km from the island were
surveyed regularly from January through July. Xantus’s Murrelets were counted within 150 m of the ship. Peak
Xantus’s Murrelet densities were observed in 1976 and 1977 from March to May, during peak nesting activity.
Xantus’s Murrelets were found most often in the western, more oceanic waters adjacent to the island. Xantus’s
Murrelets were never seen within 0.5 km of shore. During the breeding season, they were most common within
6.5 km from shore (1975 and 1976) and between 2.5 and 8.5 km (1976). In late May, birds moved farther