2 research outputs found
Recommended from our members
The Breeding Ecology and Foraging Niche of Aleutian Terns (Onychoprion aleuticus) in the Kodiak Archipelago, Alaska
The Aleutian tern (Onychoprion aleuticus) is a species of high conservation concern in Alaska due to large declines at known breeding locations since the 1960s. Due to the small population size and ephemeral behavior of this species on the nesting grounds, there is little basic biological information available and data gaps have hindered the identification of potential drivers of the population decline. Significant unknowns include rates of and factors influencing nest survival, and key prey types across the breeding season. To investigate these questions, I used a combination of nest cameras and nitrogen (δ15N) and carbon (δ13C) stable isotope analysis of eggshell membranes to estimate daily nest survival, determine chick diet composition, and to estimate pre-laying female Aleutian tern diets from 2017 to 2020 in the Kodiak Archipelago, Alaska. A total of 148 nests, 105 observed using trail cameras, were incorporated into a nest survival analysis, 81 eggshell membrane samples were analyzed for stable isotope values, and 1313 photographs of prey deliveries used to assess chick diets. I used the nest survival model in program MARK to estimate daily nest survival (DNS) rates as a function of colony location, year, within-season time trends, vegetation cover categories and height, and six weather covariates. The nest survival modeling indicated that survival was higher during 2019= 2020 (2017=2018: \widehat{\beta\ }= -0.87, 95% CI -1.27, to -0.47) with a significant interaction between year and colony. Our final competitive model set also suggested that DNS increased with average vegetation height and decreased later in the season. Stable isotope analysis indicated that δ13C values were higher in 2017 than 2018-2020. Bayesian mixing models estimated that the diet composition of Aleutian terns was equally nearshore and offshore prey types, but that 2017 had a larger proportion of prey items from the nearshore community than 2018 – 2020. Isotopic biplot standard ellipse areas were the largest in 2017, indicating a diet more varied than 2018 - 2020. Chick diet varied between years (χ2= 75.19, df = 9, p-value < 0.001), and this finding was mainly influenced by higher than expected numbers of gadids, a low quality prey, being provisioned to chicks in 2017. Overall, the importance of the year effects in both studies suggests food availability was at its lowest in 2017 and increased through 2020. A major marine heatwave was present in the Gulf of Alaska from 2014-2016, and my results suggest some effects of this anomalous event lingered even after temperatures returned to normal. Additionally, the importance of colony site in both nest survival and diet indicates that local factors may also drive significant variation in Aleutian tern productivity across their Alaskan range. These findings suggest that the Alaskan breeding population of Aleutian terns may continue to decline as the effects of climate change alter the North Pacific Ocean. The importance of colony site may allow managers to buffer this food-related decline by managing predator access and for optimal vegetation characteristics at colony sites with the most reliable access to prey resources
Active breeding seabirds prospect alternative breeding colonies
International audienceCompared to other animal movements, prospecting by adult individuals for a future breeding site is commonly overlooked. Prospecting influences the decision of where to breed and has consequences on fitness and lifetime reproductive success. By analysing movements of 31 satellite- and GPS-tracked gull and tern populations belonging to 14 species in Europe and North America, we examined the occurrence and factors explaining prospecting by actively breeding birds. Prospecting in active breeders occurred in 85.7% of studied species, across 61.3% of sampled populations. Prospecting was more common in populations with frequent inter-annual changes of breeding sites and among females. These results contradict theoretical models which predict that prospecting is expected to evolve in relatively predictable and stable environments. More long-term tracking studies are needed to identify factors affecting patterns of prospecting in different environments and understand the consequences of prospecting on fitness at the individual and population leve