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The probability of Blue‐footed Booby Sula nebouxii fledglings becoming reproductive adults is maximal when one parent is old and the other young, and minimal when both are old or young. No mechanism has been identified to explain this pattern, but here we showed that nestlings with different‐aged parents are the least infested with ticks. This result constitutes preliminary confirmation of the hypothesis that the effect of combined parental ages on probability of recruitment is mediated by offspring immunocompetence. The contribution of immunocompetence and parental care to these parental age effects needs to be unravelled. [ABSTRACT FROM AUTHOR]

The function of female birds' extra-pair (EP) behavior has remained an unresolved question in ornithology and behavioral ecology for > 30 yr. The genetic compatibility hypothesis (GCH) proposes that females benefit by acquiring biological sires that yield more heterozygous, and therefore fitter, offspring than their social mates. We used ten polymorphic microsatellite loci to test GCH predictions and its assumption that fitness increases with heterozygosity in blue-footed boobies Sula nebouxii, a long-lived tropical seabird. Our predictions were not supported. Heterozygosity was uncorrelated with quality indicators (fledging probability, fledgling or adult body size or mass, adult ornamentation, mean breeding success). Females were no more likely to have EP behavior or chicks when their social mates were less heterozygous or compatible, nor were EP males more heterozygous or compatible than the males they cuckolded. Finally, EP chicks were no more heterozygous than within-pair chicks overall or in half-sib comparisons, nor were within-pair chicks from all-within-pair nests more heterozygous that those with EP nest-mates. There are both methodological and biological explanations for these consistently negative results. Inadequate sample size is possible but unlikely, since our samples were comparable or larger than those of similar studies with significant findings. Lack of identity disequilibrium (within-individual heterozygosity correlation) among our marker loci could be responsible, and suggests either insufficient marker coverage or lack of inbreeding, bottleneck, and/or admixture. An independent social pedigree revealed infrequent inbreeding, suggesting that pressure on females to select sires that maximize offspring heterozygosity may be genuinely lax. Alternatively, it is possible that the GCH is only upheld when selection on young is strongest; this would not be detected in our sample, which was taken during an extremely productive year. Whatever their cause, our results expand the taxonomic breadth of avian EP behavior analyses and should be considered in future evaluations of the GCH. [ABSTRACT FROM AUTHOR]

The evolution of remating and prolonged pair bonds in animals has generally been explained in terms of improved coordination and cooperation between familiar individuals, but costs of mate familiarity have rarely been considered. A possible cost for males is increased risk of losing paternity if familiarity enables females to detect when alternative sires are desirable, evade mate guarding or invest more in infidelity. To test whether this familiarity cost exists, we examined whether extrapair paternity increases with bond length in the socially monogamous blue-footed booby, Sula nebouxii, using microsatellite-based analysis of 384 broods. Extrapair paternity increased from 9.4% of broods in first pairings to 21.6% in second pairings, then declined to 7.5% in third through eighth pairings. On their first remating with a female, males faced enhanced risk of losing paternity, but thereafter the risk was no greater than on first matings. However, after loss of paternity, males were no more likely to divorce. Effects of familiarity on extrapair paternity could influence the evolution and taxonomic distribution of remating and prolonged pair bonding in socially monogamous animals. [ABSTRACT FROM AUTHOR]

Individual variation in sexual fidelity and extrapair paternity (EPP) is widely attributed to environmental heterogeneity, but the only variables known to be influential are food abundance and density of conspecific breeders (potential extrapair partners). Habitat structure is thought to impact EPP but is rarely measured and, when considered, is usually confounded with food abundance and predation pressure. To sidestep these confounds, we tested whether EPP is associated with habitat structure variables and with local conspecific density in a species whose nesting habitat is not used for feeding and lacks predators. In a blue-footed booby, Sula nebouxii , colony, the probability of EPP in a female's nest was highest in parts of the study plot where there were few obstacles to locomotion, and was quadratically related to local density of sexually active males, even though local males did not sire the EP chicks. The probability of a male breeder siring EP (extrapair) chicks elsewhere was quadratically related to local density of sexually active males around his nest. From these patterns we infer that both sexes may foray for EP interactions, that males and females nesting at intermediate density are most likely to be accessed by forayers, and that obstacles in the vicinity of a female's nest constrain access of foraying males. To our knowledge, this is the first demonstration that individual variation in EPP is associated with habitat structure in the absence of confounding variation in food availability, predation pressure or breeder quality, and the first evidence that EPP opportunities of female and male breeders are reduced by high density of conspecific breeders above a particular threshold. [ABSTRACT FROM AUTHOR]