Micro and macroclimate effects on reproductive performance of Common Eiders

The physical environment has a strong influence on the lives or organisms by limiting the way energy is gained and expended determining the capacity of organisms to invest in activities like reproduction. The avian nest site and structure, through its effects on the thermal conditions of the proximal environment of the incubating parent can affect several aspects of an individual’s reproductive success. On a larger scale, characteristics of the oviposition site can impact the spatial distribution of a species and consequently several aspects of population dynamics. In this thesis I investigate the importance of the thermal environment and nesting habitat on the reproductive performance of a sea duck, the Common Eider (Somateria mollissima) breeding in a cold environment. First I described the spatial variation in nest distribution in relation to female’s and nest attributes. Females of similar quality formed aggregations of nests and clusters of high productivity were occupied earlier in the season and at higher densities. Eiders seemed to choose to nest sites based on biotic (conspecifics) rather than abiotic (microclimate) cues. By providing females with artificial shelters I tested some of the effects of microclimate on individual physiology and use of energy during incubation. Females experienced improved microclimatic conditions provided by well-sheltered nest-sites. Nest shelter conferred advantages both to incubating females by allowing energy savings and to their clutches by providing more stable incubation conditions. Shelter did not have an appreciable effect on the female’s stress response. However, in exposed areas, females with high levels of corticosterone hatched a lower proportion of eggs than females with low corticosterone. Behavioural and functional aspects nest construction were tested first, by removing down from nests on repeated occasions throughout incubation and then by testing the effects of different amounts of down on the microclimate of incubation. Females did not replace the removed down suggesting the existence of constrains on the allocation of down to the nest. Large amounts of down in the nest contributed to more stable incubation conditions but females were able to counterbalance poor nest insulation and keep incubation temperature constant but the costs of doing this are unclear. Finally, I assessed the influence of environmental variability on the onset of incubation and short-term fluctuations in population size for the study colony with data from 1977 to 2006. I found that after mild winters female Eiders lay earlier in the season perhaps because milder conditions allow them to attain the necessary body condition for reproduction sooner. Summer temperature had a lagged effect (2 yr) on colony size that could be related to the delayed maturity (age at first reproduction) presented by Common Eiders and the influence of climate on influence recruitment rate to the population. The evidence presented here shows that Common Eiders are strongly influenced by their thermal environment on reproduction but by choosing a good nest they can ameliorate those effects. However nest site selection seems to be strongly linked to female quality rather than to nest properties