• An ecological-physiology perspective on seabird responses to contemporary and historic environmental change

      Will, Alexis P.; Kitaysky, Alexander; Breed, Greg; Powell, Abby; Springer, Alan (2017-05)
      The chapters included in this dissertation implement an ecological-physiology approach to understanding how long-lived marine organisms, using seabirds as a model, respond to changes in the environment. Many seabird populations are governed by bottom-up processes, yet efforts to connect prey dynamics and parameters such as breeding performance often yield mixed results. Here I examined how individual foraging behavior and nutritional status change at the inter-annual, decadal, and multi-decadal scale. I validated that the concentration of the avian stress hormone in seabird feathers is indicative of their exposure to nutritional stress. I then used this technique to show that young seabirds (Rhinoceros auklets, Cerorhinca monocerata) that experience variable foraging conditions during their prolonged nestling period incurred higher nutritional stress when provisioned with prey that was relatively low in energy content. On the other hand, when examining adult foraging behavior, a signal of environmental variability was lost in the noise of changing diets. Foraging behavior of adults appeared to be highly flexible and less informative in regard to detecting an environmental change. I used stable isotope analysis to re-construct the isotopic niche dynamics (where and at what trophic level seabirds were obtaining prey) and partitioning of food resources for three abundant seabirds (common and thick-billed murres, Uria aalge, and U. lomvia, respectively; and black-legged kittiwakes, Rissa tridactyla) breeding in the southeastern Bering Sea under cold and warm states of the ecosystem. Access to diverse habitat reversed how seabirds partitioned prey during food shortages: seabirds with access to multiple habitats contracted their isotopic niche during food-limited conditions in contrast to the expansion of the isotopic niche observed for seabirds with access to only one type of habitat. Finally, I measured nutritional stress and stable isotope signatures (carbon and nitrogen) in contemporary and historic red-legged kittiwake (Rissa brevirostris) feather samples to examine how birds breeding on St. George Island have responded to changes in summer and winter conditions in the Bering Sea over time. Red-legged kittiwakes were less nutritionally stressed during warm summers and winters. It is not clear, however, whether all seabirds would do well if the Bering Sea were to break with its pattern of oscillating between warm and cold conditions. Prey for these birds may either be negatively affected by continuously warm conditions (murres and black-legged kittiwakes feeding on juvenile pollock, Gadus chalcogrammus) or the conditions that are most beneficial to the prey are not known (red-legged kittiwakes feeding on myctophids). With this work I suggest that measuring nutritional stress in feathers and using stable isotope analysis to characterize foraging niches may document more dynamic responses to changes in the environment than population level parameters such as breeding performance. To do so, however, requires a better understanding of the relationship between these individual-level responses and fitness.
    • Estimating seabird abundance: a case study in Kenai Fjords National Park, Alaska

      Curl, Jennifer; Mulder, Christa; Schmidt, Joshua; Lindberg, Mark (2018-05)
      Estimation of breeding seabird population size and trends are integral components of studies or programs seeking to understand how seabird populations respond to changes in marine or coastal environments, to identify threatened or declining species, and to inform management actions and decisions. In Chapter 1, I conduct a review of the challenges, considerations, tools, and methods involved in efforts to estimate and monitor breeding seabird abundance. I discuss challenges in terms of two broad categories: 1) seabird life history, behavior, and breeding environments, and 2) challenges inherent to survey methods and logistics. I introduce methods and tools used to access seabird colonies, detect birds, and design methods to collect and analyze count or abundance data. The focus of Chapter 2 is to find effective methods to estimate the breeding abundance of glaucous-winged gulls (Larus glaucescens) in Kenai Fjords National Park (KEFJ), Alaska, which has been designated as an Important Bird Area (IBA) for this species. There are numerous inherent challenges in this effort, as L. glaucescens breeds in widespread colonies on vertical cliff faces of the fjords and associated islands, and their nests are not visually detectable from boat-based surveys. I conducted and compared field counts to replicated photographic counts, and found enough variability between replicates for both count methods to preclude calculation of precise abundance estimates using counts alone. I then developed a more intensive method of analyzing images using a modified mark-resight (MR) approach to identify all potential nest locations, and I took advantage of both attendance and behavioral data collected from repeat photographs to estimate what proportion of them have a high probability of containing nests. I quantified two potential survey error rates and their effects on the results of our modified MR approach. Finally, I considered temporal and environmental factors likely to affect both repeated counts and the results of my modified MR approach. I found that: 1) the modified MR approach provided a better approximation of breeding abundance than simple field counts and addressed variability between replicate surveys; 2) low misidentification survey error rates had a negligible effect on the results; and 3) general patterns of attendance of birds at colonies were influenced by different factors than the attendance patterns at locations that were likely nests. I recommend similar methods for other colonial or cliff-nesting bird species, species that have variable attendance, or species that make nests that are hard to see. These methods may also be helpful in areas that are remote or infrequently visited or where time in the field is a limiting factor in how much data can be collected.