Trevor B. Haynes

Diet of yellow-billed loons ( Gavia adamsii ) in Arctic lakes during the nesting season inferred from fatty acid analysis

Understanding the dietary habits of yellow-billed loons (Gavia adamsii) can give important insights into their ecology, however, studying the diet of loons is difficult when direct observation or specimen collection is impractical. We investigate the diet of yellow-billed loons nesting on the Arctic Coastal Plain of Alaska using quantitative fatty acid signature analysis. Tissue analysis from 26 yellow-billed loons and eleven prey groups (nine fish species and two invertebrate groups) from Arctic lakes suggests that yellow-billed loons are eating high proportions of Alaska blackfish (Dallia pectoralis), broad whitefish (Coregonus nasus) and three-spined stickleback (Gasterosteus aculeatus) during late spring and early summer. The prominence of blackfish in diets highlights the widespread availability of blackfish during the early stages of loon nesting, soon after spring thaw. The high proportions of broad whitefish and three-spined stickleback may reflect a residual signal from the coastal staging period prior to establishing nesting territories on lakes, when loons are more likely to encounter these species. Our analyses were sensitive to the choice of calibration coefficient based on data from three different species, indicating the need for development of loon-specific coefficients for future study and confirmation of our results. Regardless, fish that are coastally distributed and that successfully overwinter in lakes are likely key food items for yellow-billed loons early in the nesting season.

Diel Shifts in the Marine Distribution of Marbled Murrelets Near Port Snettisham, Southeast Alaska

Abstract. Little is known about seabird distributions at night. Densities of Marbled Murrelets (Brachyramphus marmoratus, hereafter “murrelets”) and potential prey were determined along fixed-width transects in spring and summer of 2007 and 2008, and compared during night and day in two regions of Port Snettisham, near Juneau, Southeast Alaska. Murrelets moved from a shallower, more sheltered inner region, used during the day for foraging and staging for inland flights (2007 night densities = 15 ± 13 murrelets·km-2; 2007 day densities = 172 ± 67 murrelets·km-2), to a deeper, more exposed outer region, further from shore, during dark hours (2007 night densities = 113 ± 61 murrelets·km-2; 2007 day densities = 41 ± 23 murrelets·km-2). Prey school density and relative prey density were significantly higher at night in the inner region compared with the outer region (2.2 times higher prey school density and 3.8 times higher relative prey density), suggesting that murrelets were not redistributing themselves to forage on fish prey. A more likely explanation for why murrelets move from day use areas to night use areas is to avoid predators such as Bald Eagles (Haliaeetus leucocephalus), Great Horned Owls (Bubo virginianus) and various mammals.

A Comparison of the Hyposaline Tolerances of Black Prickleback (Xiphister atropurpureus) and Penpoint Gunnel (Apodichthys flavidus)

Abstract We compared the hyposalinity tolerances of black prickleback (Xiphister atropurpureus) and penpoint gunnel (Apodichthys flavidus) that were collected in an intertidal area during a low-tide near Bamfield, British Columbia. We found black pricklebacks completely removed from the ebbing tide where they may be exposed to hyposaline conditions for up to five hours. Conversely, penpoint gunnels were found in larger tidepools or subtidal areas where they are less likely to be exposed to hyposaline conditions. The tolerance of each species was determined by measuring oxygen consumption (µmol·g·h) and counting opercular beats (per minute) in full-strength (∼30 ppt) and dilute seawater (∼6 ppt). Black pricklebacks (N = 10) consumed oxygen at a significantly lower rate (P = 0.001) in dilute seawater when compared to full-strength seawater, whereas there was no significant difference in consumption rate by penpoint gunnels (N = 10). The rate of opercular beats for both species significantly decreased in dilute seawater. Black pricklebacks showed a greater decrease in breathing rate, and opercular beating stopped completely in nine of the ten dilute seawater trials for periods ranging from 10 – 60 minutes. The lower oxygen consumption and breathing rate of black pricklebacks suggests that this species may have the ability to depress metabolic activity to remain in the intertidal zone during an ebb tide. These findings indicate that physiological adaptations may be a factor in the habitat portioning between black pricklebacks and penpoint gunnels.