Family Structure Influences Mate Choice
in White-Fronted Bee-Eaters

Wrege, P.H. and Emlen, S.T. (1994). Behavioral Ecology and Sociobiology, 35:185-191.

White-fronted bee-eaters live in patrilocal, extended family groups in which several pairs may breed simultaneously and in which helping behavior by nonbreeders is common. The composition of a male's family, and his social position within it, are major predictors of his expected reproductive success. For females, the dispersing sex, a decision to pair necessitates forfeiting any potential fitness benefits available through helping in her family, in favor of the potential benefits of breeding in the male's family. Using a set of equations that incorporate the social and non-social predictors of nesting success, we develop a payoff matrix for the expected fitness (current and future) of pairing with different categories of males. Predictions generated from this payoff matrix were supported by data: (1) Females that could help close kin (and thus garner large indirect benefits) tended to remain unpaired. (2) Males with social characteristics associated with low expected reproductive success were more often rejected as potential mates by females. (3) "High-quality" males, those with potential helpers of their own, were nearly always paired. Simulation analyses were used to investigate female pairing decisions in more detail, and to test various hypotheses about possible decision rules. We demonstrate that pairing females incorporate an assessment of the family structure of potential partners into their mate choice decisions. Such social characters will prove to be important components of mate choice decisions in many species where kinship and dominance considerations influence the likelihood, or success, of breeding.