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Date of Award


Document Type

Thesis-ISU Access Only

Degree Name

Master of Science (MS)


School of Biological Sciences

First Advisor

Charles F. Thompson

Second Advisor

Scott K. Sakaluk


In many bird species, females produce fewer offspring than they are capable of raising. One hypothesis to account for this widespread pattern is that an increase in current reproductive effort might come at the expense of a female's survival prospects and likelihood of future reproduction. To test the hypothesis that clutch size in altricial birds is limited by such costs, I experimentally induced female house wrens (Troglodytes aedon) to lay more eggs in their first broods than they normally would, so that the cumulative costs of increasing clutch size could be evaluated across all periods of the breeding cycle: egg-laying, egg-incubation, and nestling-provisioning, and among breeding seasons. Experimental females successfully raised more offspring in the first brood than control females. In the second brood, experimental females laid the same number of eggs as control females, but, after suffering modest intra-seasonal reproductive costs through reduced hatchling survival, subsequently fledged fewer offspring in their second broods. Despite lower second-brood success, experimental females produced more high-quality, first-brood offspring than control females, which are more likely to recruit to the breeding population. Furthermore, the manipulation did not influence inter-seasonal reproductive success, as experimental females and their offspring were equally likely to return to the study site and had similar reproductive success. Thus, female house wrens in the study population are able to produce more high-quality offspring than they normally attempt to raise. I suggest two possible explanations for these surprising findings: (1) females may buffer their clutch size against the risk of predation or other catastrophic events that would lead to the total loss of their nests, and (2) because most breeding females in our population are immigrants, their life histories may not be adapted to the current environmental conditions observed on our study area.


Imported from ProQuest Hodges_ilstu_0092N_10201.pdf


Page Count


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