Experimental cross-fostering of eggs reveals effects of territory quality on reproductive allocation

• Published in: Behavioral ecology 2018-09, Vol.29 (5), p.1190-1198
• Main Authors: Poorboy, Dylan M, Bowers, E Keith, Sakaluk, Scott K, Thompson, Charles F
• Format: Article
• Language: English
• Subjects: Original
• ISSN: 1045-2249; 1465-7279
• DOI: 10.1093/beheco/ary098

In territorial songbirds, both parental and territory qualities influence resource allocation to offspring, but their relative contributions are unclear. We experimentally decoupled these 2 factors, allowing us to examine the contribution of territory quality, alone, to investment in offspring. We showed that territory quality influences provisioning of nestlings through a prenatal effect on the composition of eggs laid, rather than a postnatal effect of the quality of territory on which provisioning occurred. Abstract Parental and territory quality are often correlated in territorial birds, and both factors influence the resources allocated to offspring. Surprisingly, the relative contribution of these two components of variation in parental investment remains obscure. We experimentally decoupled the normal covariation between parental quality and territory quality to test the hypothesis that territory quality influences female prenatal and postnatal reproductive allocation. Territories were categorized into low-, intermediate-, and high-quality based on fledging success of nests over the previous 6 years (nesting sites are fixed in space).To decouple covariation between territory quality and individual quality, nestbox entrance size was increased on high-quality territories and left small on poor-quality sites because house wrens (Troglodytes aedon) prefer small over large entrances to their nest sites. We found a significant prenatal effect of territory quality on nestling provisioning: when reared on intermediate-quality territories, nestlings hatching from eggs produced on low-quality territories were provisioned at a higher rate than those hatching from eggs produced on high-quality territories. We propose that the increased provisioning was brought about by increased nestling begging mediated by a maternally derived compound, such as corticosterone, transferred to the eggs of stressed females in poor-quality habitat.