Date of Award
Master of Science (MS)
School of Biological Sciences
Charles F Thompson, Scott K Sakaluk
Alysia D. Vrailas-Mortimer
In a number of bird species, eggs laid by females breeding in the same population can vary extensively in the extent of their eggshell pigmentation, but the adaptive significance of this intraspecific variation remains unknown. One hypothesis posits that shell pigmentation is an honest signal of female quality that reflects her level of oxidative stress, one that is used by males to inform their subsequent paternal investment. We employed a reciprocal clutch cross-fostering design to test whether provisioning by male house wrens (Troglodytes aedon) responds to the clutch pigmentation of their mates. In experimental replicates, dark clutches were swapped with light clutches two days into incubation, whereas in control replicates, light clutches were swapped with light clutches, or dark clutches with dark. Shortly before hatching, clutches were returned to their original nest to avoid the confounding effect of nestling quality on male provisioning effort. We found no effect of clutch pigmentation on male provisioning effort. We did find, however, that females that laid lighter clutches were significantly older than females that laid darker clutches and tended to be of greater structural body size. We also found that nestlings hatching from lighter clutches had a significantly higher size-corrected body mass at brood-day 11, a measure that is strongly predictive of survival and recruitment to the breeding population. Although it seems likely that male house wrens are fully capable of observing eggshell pigmentation and may be able to infer female quality from it, males do not use this information when provisioning their young. This may be because of constraints on reproductive opportunities imposed by a socially monogamous mating system, restricting the pool of potential female partners, in concert with a short average lifespan.
Hodges, Kara E., "Connecting the dots: exploring the relationship between avian eggshell pigmentation and paternal provisioning effort" (2019). Theses and Dissertations. 1157.