Monitoring reproductive success, prey species composition, and colony size of
marine birds has been proposed as a method of assessing changes in marine
systems that are otherwise difficult to sample (Cairns 1987). I measured inter-annual
and intra-seasonal variability in reproductive parameters, taxonomic
composition of the diet, and adult body condition of Crested Auklets (Aethia
cristatella) and Least Auklets (A. pusilla) at 2 colonies near the village of Savoonga,
St. Lawrence Island, Alaska during the 2000-2002 breeding seasons to evaluate how
reproductive success of planktivorous seabirds is related to diet. I also assessed the
utility of two methods of population monitoring (surface counts and mark-resighting)
for detecting annual changes in breeding populations of Crested and Least auklets
during the 2001 and 2002 breeding seasons on the Kitnik colony.
Average reproductive success was generally high (>60% of nests) for both
auklet species during the 3 years of the study, but differed among years. Median
hatching dates for both species were 2 weeks earlier in the year of highest
reproductive success (2002), compared to the previous 2 years. In all 3 years, the
diet of Crested Auklets was predominantly euphausiids, while the diet of Least
Auklets consisted primarily of calanoid copepods, but species composition of the diet
differed among years for both species. Crested and Least auklets consumed more of
the large, lipid-rich copepod Neocalanus cristatus in 2002 than in the other 2 years
of the study. The year of lowest reproductive success (2001) was associated with
low prevalence of euphausiids in Crested Auklet diets late in the chick-rearing period
and high prevalence of the small, low-lipid copepod Calanus marshallae in Least
Auklet diets.
I observed an increase in total body mass of Crested Auklets during the 2002
breeding season, whereas total body mass declined through the breeding season in
the other 2 years. Seasonal changes in adult body mass of Crested Auklets may,
therefore, be a useful indicator of food availability. Average body mass of Least
Auklets declined in all 3 years, but was lowest in 2001, suggesting that low adult
body mass of Least Auklets may reflect poor foraging conditions. Fat reserves of
breeding auklets during egg-laying were not highly variable among or within breeding
seasons and therefore were not a sensitive predictor of subsequent breeding
success.
Counts of Crested Auklets in plots on the colony surface were highest in areas
of large average boulder size; Least Auklet surface counts were not as variable
among plots. Maximum counts of both species of auklets in plots did not differ
between years. Patterns of colony surface attendance during the breeding season,
however, did differ between years. The colony surface attendance of both auklet
species after hatching was higher in the year of high reproductive success.
Preventing nest initiation by covering plots with tarps did not reduce subsequent
colony surface attendance during chick-rearing (after the tarps were removed) for
either species, suggesting that reproductive success, independent of differences in
food availability, did not cause a difference in colony surface attendance. I estimated
abundance of Least Auklets nesting in two 100-m�� plots using mark-resight methods.
I concluded that surface counts may provide an indication of among-year differences
in colony attendance, but underestimate the number of breeding individuals by a
factor of 10. Mark-resighting techniques show more promise for detecting changes
in the number of breeding pairs. Reproductive success, adult body mass, and post-hatch
colony attendance of Crested and Least auklets appear positively associated
with zooplankton availability, particularly the prevalence of N. cristatus in the diet.
Annual monitoring of these 3 parameters, together with diet composition, are
important for understanding how both natural and anthropogenic climate change
may affect trophic structure of the northern Bering Sea ecosystem. / Graduation date: 2004
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/30898 |
| Date | 22 March 2004 |
| Creators | Gall, Adrian |
| Contributors | Roby, Daniel D. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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