Blue-Footed Boobies: Sibling Conflict and Sexual Infidelity on a Tropical Island

In Blue-Footed Boobies, Hugh Drummond presents a lifetime field study of one of the planet’s most charismatic and observable birds, focused on two themes of human relevance: aggressive competition between siblings and monogamous pair-bonding combined with frequent infidelity. In an account peppered with research anecdotes, he immerses readers in a bustling blue-footed booby colony where social manipulation and life-and-death dramas are the stuff of family life. Here, dominant elder chicks prefer to bully their siblings into abject submission rather than killing them and younger siblings’ susceptibility to subordination is an evolved ability. The narrative expands to survey the colorful strategies used by young birds and mammals to compete with siblings ruthlessly, with restraint or with courtly manners, scrutinize the role of parents in sibling conflict, and assess the lifetime impacts of bullying on those that survive. Next, a compelling eye-witness account of monogamous partnerships in blue-foots reveals a world disturbingly familiar to humans. After displaying their beauty and physical prowess to each other, females and males select partners and commit to months of relentless parental care, sharing duties and making decisions jointly. Half of them renew their bond the following year, and renewers are more efficient and successful than first-time partners. But colonies of bonded blue-foot pairs are hotbeds of infidelity! Nearly all females and males carry on semi-secret liaisons with 1-3 neighbors, roughly one third of them copulate repeatedly with those extra partners, and one in ten males ends up caring for another male’s chick. Countermeasures include surveillance, aggression and partner-switching, and males unsure of paternity sometimes resort to infanticide. Drummond discusses a panoply of plausible biological functions of infidelity. Sibling competition and sexual conflict are widespread in animal species in which two partners raise contemporaneous offspring together, and notorious in humans. In the final chapter Drummond argues for a common evolutionary cause in the blue-foot and human lineages, despite the psychology of their behavior being quite different: whereas boobies thoughtlessly follow routines of predictable actions, humans experience inclinations and urges they can implement in diverse ways, or choose to veto.