Differences in size between first and replacement clutches match the seasonal decline in single clutches in Tree Swallows Tachycineta bicolor

Abstract

The seasonal decline in clutch size in birds can be a response to the environmentally conditioned decrease in prospects for offspring or a consequence of a lower physical ability of late‐breeding females. To find out which of the explanations apply in Tree Swallows Tachycineta bicolor, we assessed whether replacement clutch size in this species is affected by an individual female's ability to lay a certain number of eggs. To do this, we measured the decline in clutch size as a function of laying date between first and replacement clutches in individuals that re‐nested following natural failure, and compared this with the rate of decline in clutch size with laying date for Tree Swallows that laid only a single clutch in that season. Additionally, we assessed whether the clutch size and the rate of its seasonal decline varied across years. We accounted for the truncated and under‐dispersed nature of clutch size data by using a Bayesian approach in the analysis. We found little variation in the rate of clutch size decline across years at our breeding site. Accounting for this seasonal decline in clutch size, mean clutch size was similar between single‐time breeding females and those that laid replacement clutches, implying that the number of eggs laid on the second attempt by female Tree Swallows is determined by laying date, rather than by the female's physical ability to produce a clutch of a certain size.

Causes of seasonal decline in reproduction of the cooperatively‐breeding acorn woodpecker

“…Prior studies have yielded variable results in terms of the relative importance of the quality and timing hypotheses. In experimental studies manipulating the timing of nesting attempts, Christians et al (2001) found that the seasonal decline in clutch size of European starlings Sturnus vulgaris was due entirely to differences between females, whereas Wiggins et al (), Verhulst et al (), and Karagicheva et al () concluded that timing effects were primarily responsible for declines in clutch size observed in collared flycatchers Ficedula albicollis , great tits Parus major , and tree swallows Tachycineta bicolor , respectively. In a noteably thorough and thoughtful analysis, Westneat et al () showed that clutch size in house sparrows Passer domesticus was affected by both lay date (timing) and differences among females (female quality) along with other factors, including attempt order and the interaction between attempt order and lay date.…”

“…A seasonal decline in reproductive output is one of the most ubiquitous patterns found in temperate birds and has been studied extensively for over 70 years (Lack , Klomp , Rowe et al , Pärt et al , Weiser et al ). Conclusions from these studies, which include both empirical and experimental approaches, have varied widely, but have in several cases provided evidence for both the hypotheses that earlier‐breeding birds are of higher quality (the ‘quality’ hypothesis; Christians et al 2001), and that conditions intrinsically decline seasonally independent of bird quality (the ‘timing’ hypothesis; Verhulst and Nilsson , Karagicheva et al ).…”

Annual chronotypes functionally link life histories and life cycles in birds

“…The opposite should hold for birds with "slow" life histories. Therefore, when survival-reproduction trade-off is mediated by timing of breeding, resource allocation to either fitness component can be optimized by fine-tuning the timing of spring activities, as it is often found in birds breeding in seasonal environments at temperate and northern latitudes (Drent & Daan, 1980;Helm & Lincoln, 2017;Karagicheva, Liebers, et al, 2016;Öberg, Pärt, Arlt, Laugen, & Low, 2014).…”