Demographic profiles and environmental drivers of variation relate to individual breeding state in a long-lived trans-oceanic migratory seabird, the Manx shearwater

Understanding the points in a species breeding cycle when they are most vulnerable to environmental fluctuations is key to understanding interannual demography and guiding effective conservation and management. Seabirds represent one of the most threatened groups of birds in the world, and climate change and severe weather is a prominent and increasing threat to this group. We used a multi-state capture-recapture model to examine how the demographic rates of a long-lived trans-oceanic migrant seabird, the Manx shearwater Puffinus puffinus, are influenced by environmental conditions experienced at different stages of the annual breeding cycle and whether these relationships vary with an individual’s breeding state in the previous year (i.e., successful breeder, failed breeder and non-breeder). Our results imply that populations of Manx shearwaters are comprised of individuals with different demographic profiles, whereby more successful reproduction is associated with higher rates of survival and breeding propensity. However, we found that all birds experienced the same negative relationship between rates of survival and wind force during the breeding season, indicating a cost of reproduction (or central place constraint for non-breeders) during years with severe weather conditions. We also found that environmental effects differentially influence the breeding propensity of individuals in different breeding states. This suggests individual spatio-temporal variation in habitat use during the annual cycle, such that climate change could alter the frequency that individuals with different demographic profiles breed thereby driving a complex and less predictable population response. More broadly, our study highlights the importance of considering individual-level factors when examining population demography and predicting how species may respond to climate change.

Mitigating impacts of invasive alien predators on an endangered sea duck amidst high native predation pressure

Invasive species represent a major threat to global biodiversity by causing population declines and extinctions of native species. The negative impacts of introduced predators are well documented, yet a fundamental knowledge gap exists regarding the efficiency of potential mitigation methods to restore the ecosystem. Other understudied aspects concern prey behavioural antipredator responses and the historical context of native predator-prey interactions, which may moderate invasion impacts on native prey. Invasion impacts of American mink (Neovison vison) and raccoon dog (Nyctereutes procyonoides) into the Baltic Sea archipelago are poorly understood, and the efficiency of removal efforts as a means to alleviate depredation pressure on native prey is debated. Here, we examine the effectiveness of invasive predator removal on ground-nesting female common eider (Somateria mollissima) mortality, breeding success and breeding propensity over a nine-year period, while controlling for predation risk imposed by the main native predator, the white-tailed eagle (Haliaeetus albicilla). Our results clearly show that intensified removal of American minks and raccoon dogs decreased the number of female eiders killed during nesting, while improving both nesting success and breeding propensity. Such obvious positive effects of invasive predator removal are particularly noteworthy against the backdrop of a soaring eagle population, indicating that the impacts of invasives may become accentuated when native predators differ taxonomically and by hunting mode. This study shows that invasive alien predator removal is a cost-efficient conservation measure clearly aiding native fauna even under severe native predation pressure. Such cost-effective conservation actions call for governmental deployment across large areas.

Contrasting effects of the onset of spring on reproductive success of Arctic-nesting geese

Breeding output of geese, measured as the proportion of juveniles in autumn or winter flocks, is lower in years with a late onset of spring in some species, but higher in at least one other species. Here we argue that this is because the timing of spring affects different stages of the reproductive cycle differently in different species. Because the effects on 2 different stages are opposite, the combined effects can result in either a positive or a negative overall effect. These stages are the pre-laying, laying, and nesting phase on the one hand; and the hatchling, fledgling, and juvenile phase on the other hand. The first phase is predominantly positively affected by an early snowmelt, with higher breeding propensity, clutch size, and nest success. The second phase in contrast is negatively affected by early snowmelt because of a mismatch with a nutrient food peak, leading to slow gosling growth and reduced survival. We argue that recognition of this chain of events is crucial when one wants to predict goose productivity and eventually goose population dynamics. In a rapidly warming Arctic, the negative effects of a mismatch might become increasingly important.

Barred Owls reduce occupancy and breeding propensity of Northern Spotted Owl in a Washington old-growth forest

Protected lands like national parks are important refuges for threatened and endangered species as environmental pressures on wildlife and their habitats increase. The Northern Spotted Owl (Strix occidentalis caurina), a species designated as threatened under the Endangered Species Act, occurs on public lands throughout the western United States including Mount Rainier National Park (MRNP), Washington. With virtually no history of timber harvest or large forest disturbance within MRNP boundaries since the park’s creation in 1899, MRNP provides an ideal place to evaluate potential impacts of climate change and invasive Barred Owls (Strix varia) on the Northern Spotted Owl. We used a multi-state, multi-season occupancy model to investigate how Northern Spotted Owl occupancy dynamics and breeding propensity are related to the presence of Barred Owls, local and regional weather, and habitat characteristics at MRNP from 1997 to 2016. Historical occupancy of Northern Spotted Owl breeding territories in MRNP has declined by 50% in the last 20 yr, and territory occupancy by breeding Northern Spotted Owls also decreased, reaching a low of 25% in 2016. Occupancy rates were higher on territories with steeper terrain and breeding rates were lower when Barred Owls were detected within historical territories. Our results also indicated that breeding propensity was higher when early nesting season temperatures during March and April were higher. In addition, the ability to detect breeding Northern Spotted Owls decreased when Barred Owls were present in the territory. Habitat variables from LiDAR were not correlated with Northern Spotted Owl occupancy dynamics, likely reflecting the dominance of old-growth forest in this protected park. This study illustrates the strong relationship between Barred Owls and Northern Spotted Owl demographics and breeding site selection in a landscape where habitat loss by timber harvest and fire has not occurred.