Certainty of paternity and paternal investment in eastern bluebirds and tree swallows

Animal Behaviour
By: , and 



Extra-pair paternity is common in many socially monogamous passerine birds with biparental care. Thus, males often invest in offspring to which they are not related. Models of optimal parental investment predict that, under certain assumptions, males should lower their investment in response to reduced certainty of paternity. We attempted to reduce certainty of paternity experimentally in two species, the eastern bluebird, Sialia sialis, and the tree swallow, Tachycineta bicolor, by temporarily removing fertile females on two mornings during egg laying. In both species, experimental males usually attempted to copulate with the female immediately after her reappearance, suggesting that they experienced the absence of their mate as a threat to their paternity. Experimental males copulated at a significantly higher rate than control males. However, contrary to the prediction of the model, experimental males did not invest less than control males in their offspring. There was no difference between experimental and control nests in the proportion of male feeds, male and female feeding rates, nestling growth and nestling condition and size at age 14 days. We argue that females might have restored the males’ confidence in paternity after the experiment by soliciting or accepting copulations. Alternatively, males may not reduce their effort, because the fitness costs to their own offspring may outweigh the benefits for the males, at least in populations where females cannot fully compensate for reduced male investment.

Publication type Article
Publication Subtype Journal Article
Title Certainty of paternity and paternal investment in eastern bluebirds and tree swallows
Series title Animal Behaviour
DOI 10.1006/anbe.1997.0667
Volume 55
Issue 4
Year Published 1998
Language English
Publisher Elsevier
Contributing office(s) Alaska Science Center
Description 16 p.
First page 845
Last page 860
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