Evolutionary ecology of avian nest design and function in a variable environment

Reproduction is the only source of fitness for most organisms, which is why despite the inherent costs to an individual’s own condition, they invest their finite resources into reproductive attempts. However, individuals must weigh investment in any single attempt against any future attempts to breed because investing heavily in one attempt can reduce the likelihood of surviving to breed again. This cost of reproduction is likely to vary in relation to many factors, including environmental conditions. This thesis investigates the effects of variable environmental conditions on nest placement and structure, and incubation behaviour and duration in a passerine bird. These problems are addressed using the long-tailed tit Aegithalos caudatus, which has been studied in the Rivelin Valley, Sheffield since 1994. I used this long-term dataset to answer questions about the effects of predation on nest placement, and the influence of environmental conditions on incubation period duration and hatching success. I also conducted experiments on nests to explore how their thermal properties were affected by ambient temperature and simulated rainfall under controlled conditions. Finally, I determined the influence of environmental conditions on incubation behaviour. The probability of predation and predator type varied significantly with nest placement, but personal experience of nest predation did not affect nest placement. Nest site choice was neither a heritable trait, nor was it a result of imprinting. Variation in incubation period duration was a function of environmental conditions, and also influenced hatching success. Experiments showed that nests effectively buffered the potential impact of adverse environmental conditions (temperature and rainfall) on nest contents. Finally, females adjust their incubation behaviour in order to buffer variation in ambient temperatures, with consequences for incubation period duration and hatching success. I conclude that variability in nest-building and incubation behaviours allows individuals to adapt to their environmental conditions.