Extrapair Paternity Associated with Renesting in the American Goldfinch

Abstract

Copulations outside of the social pair bond occur in a wide range of bird species (Westneat et al. 1990, Birkhead and M0ller 1992). However, the fitness consequences of this behavior have been established only recently (e.g. Westneat 1990, Kempenaers et al. 1992, Lifjeld et al. 1993, Dunn et al. 1994, Hill et al. 1994). Failing to account for extrapair copulations (EPCs) can result in measures of reproductive success that are overestimated for some individuals and underestimated for others (Gibbs et al. 1990). Therefore, to better understand the adaptive significance of extrapair mating behavior, the degree to which EPCs result in fertilization must be assessed. This is possible with the use of molecular techniques such as DNA fingerprinting (Jeffreys et al. 1985a,b). The present study was undertaken to determine the prevalence and correlates of extrapair paternity (EPP) in a population of American Goldfinches (Carduelis tristis) by combining behavioral observations with DNA fingerprinting. The American Goldfinch is a small (ca. 12 g), sexually dimorphic cardueline finch that exhibits social monogamy (Middleton 1993; but see Middleton 1988). Because of the late initiation of breeding and the occurrence of a postnuptial molt, egg laying in southern Ontario is confined primarily to July and August (Middleton 1993). The result is a relatively synchronous breeding season in which the majority of clutches are started in the latter half of July (Middleton 1979). Both male and female goldfinches provide high levels of preand posthatching parental care. During the incubation period, males contribute indirect parental care by feeding the incubating female. Initially, adult males and females feed the nestlings in approximately equal proportions, but males gradually assume the predominant role and contribute most of the parental care after fledging (Middleton 1993). Thus, the fitness costs of cuckoldry to a pair-bonded male are high, and males guard their mates immediately before and during egg laying (Middleton 1993). According to Westneat et al. (1990), this pattern of reproduction (i.e. synchronized breeding, mate guarding by males) should reduce the potential for extrapair copulations. However, behaviors such as