P1.111 Jan. 4 How does clutch number affect clutch size? TRAVERS, Marc/S*; ZANETTE, Liana; CLINCHY, Michael; WILLIAMS, Tony/D; Simon Fraser Univ./Univ. of Western Ontario; Univ. of Western Ontario; Univ. of Western Ontario/ Univ. of Victoria; Simon Fraser Univ. firstname.lastname@example.org
In 1947, David Lack suggested that the number of eggs a bird lays is more constrained by investment during brood-rearing than the costs associated with egg production. Contrary to Lack’s contention, there is increasing evidence that females do incur significant physiological and life-history costs from investing in greater egg production. For example, Zanette et al. (Ecology, 2006) showed in free-living song sparrows that the greater the total number of clutches a female lays in a season (i.e., clutch number) the smaller the average size of those clutches, implying a cost of repeated laying. Williams (BioScience, 2005) hypothesized that the costs of egg production may result from the negative consequences of repeated exposure to reproductive hormones that are known to have widespread (‘pleiotropic’) effects on a broad range of physiological systems. The purpose of the present study is to better understand why re-nesting reduces the number of eggs a female sparrow lays in successive clutches by exploring the effects of repeated laying on a variety of physiological traits (corticosterone and prolactin levels, plasma metabolites, anemia). It was expected that females that had laid more clutches would be in worse condition (eg. higher corticosterone, more anemic). We recorded the number and size of clutches laid by song sparrows over three breeding seasons at the same sites used by Zanette et al. To obtain measures of condition, we captured female sparrows throughout the breeding season and obtained blood samples from the brachial vein. We discuss the results and implications of repeated nesting on song sparrow physiology.