abstracts of oral and poster presentations - Pacific Seabird Group

anging Thick-billed Murres, Common Murres, Rhinoceros Auklets, Razorbills, and Little Penguins.
Acceleration and depth were sampled at 32 or 64 Hz and 1 Hz, respectively, using data-loggers. Low- and highfrequency
components of acceleration provided estimates of body angle and wing stroke, respectively. Swim
speed was estimated using body angle and depth change rate. Thick-billed and Common murres made vertical
dives, but dives of the other three species were oblique. Swim speed during descent was higher for Little
Penguins than murres and Razorbills, with Rhinoceros Auklets having the lowest swim speed. During passive
ascent, alcids increased body angle and swim speed. In contrast, Little Penguins decreased body angle whilst
maintained high swim speed. During descent, Little Penguins made forward thrusts on both the up- and downstroke,
irrespective of dive depth. Thick-billed Murres, Common Murres, and Rhinoceros Auklets made
forward thrusts on both the up- and down-stroke in shallow depths but only on the down-stroke in deep depths.
There was a smaller range of surge acceleration associated with strokes in Little Penguins than alcids, indicating
that penguins swim more steadily.
DIET SHIFT IN HEERMANN’S GULLS (Larus heermanni) DURING THE NON-BREEDING SEASON
[Poster]
Walter Wehtje (walter.wehtje@csun.edu); Department of Geography, California State University, Northridge,
CA USA
Heermann's Gulls breed in the Sea of Cortez during during March–May. After breeding, they disperse
to the Pacific coast, where they congregate on sandy beaches and molt their flight feathers. During June–
September of 2003–2004, I examined the diet of Heermann's Gulls along the central coast of California by
collecting regurgitated pellets from individuals on Guadalupe Beach in San Luis Obispo County. Each pellet
was cleaned and prey remains identified. The majority of 200+ pellets examined consisted solely of shell
remains of mole crabs (Emerita analoga). This diet preference has not been recorded for this species
previously, but it is known for the closely related Gray Gull (Larus modestus) of South America. In contrast to
the Gray Gull, Heermann's Gulls appear to only feed on mole crabs during the non-breeding season. I believe
this difference is due to the energetic cost of the Heermann's Gull’s preferred surface-dipping and surfaceplunging
feeding habits. The post-breeding molt reduces their ability to forage effectively offshore, thereby
limiting them to less energetically costly feeding techniques. Indirect evidence for this conclusion comes from
the lack of juvenile Heermann's Gulls observed feeding on mole crabs during the summer months. Because
juveniles do not molt their flight feathers during their first year, they are not limited in their foraging ability,
and, hence, are the age-group most commonly encountered offshore during June–September.
DETECTION PROBABILITIES WHEN COUNTING RING-BILLED GULL NESTS ON THE GREAT
LAKES [Poster]
Chip Weseloh (chip.weseloh@ec.gc.ca) and Cynthia Pekarik; Canadian Wildlife Service, Downsview
(Burlington), ON CANADA
Nest counts were made at four Ring-billed Gull colonies on the lower Great Lakes in 1999 and 2004 for
the purpose calculating repeatability and detection probability (DP). Forty-two strip transects 5–8 m wide were
traversed by single researchers, and all gull nests within each transect were counted. On reaching the end of the
strip, the researcher turned around and recounted the nests walking in the other direction. Strips contained 32–
303 nests (mean = 99.3). Second counts ranged from 21.7% more than to 11.1% less than the first count; the
mean was 3.0% more than the first count, and 88.1% of the second transect counts were within 5% of the first
counts. Detection probability was calculated for 20 of the 42 strips by having 1–2 researchers follow the initial
single counter and paint all nests in the strip; this figure became the “true” number of nests. Detection
probabilities for individual strips ranged from 81.7–100%, the mean was 94.9%, and 55.0% of counts had a DP
of 95% or greater; 90.0% of counts had a DP of 90% or greater. These repeatabilities and detection probabilities
should be comparable for ground-nesting colonial species with minimal ground cover, e.g. Ring-billed, Herring
and California Gulls, as well as Double-crested Cormorants, and indicate a high degree of accuracy for these
species in past Great Lakes surveys.