The adaptive significance of off-lek sociality in birds: A synthetic review, with evidence for the reproductive benefits hypothesis in Long-wattled Umbrellabirds

Anecdotal evidence suggests that lekking birds exhibit considerable variation in form and degree of sociality away from the lek, yet this phenomenon has received very little theoretical or empirical research attention. Here, we provide the first synthetic literature review of off-lek sociality in birds and develop a conceptual framework for the potential adaptive function of off-lek sociality across lekking taxa. We then present a case study of the Long-wattled Umbrellabird (Cephalopterus penduliger), where we find support for the hypothesis that off-lek sociality is primarily driven by male reproductive incentives for coordinating lek attendance during the breeding season. During periods of high lekking activity, male umbrellabirds depart the lek in highly coordinated groups and maintain larger off-lek social groups relative to periods of low lekking activity. These seasonal differences in off-lek sociality do not occur in females, are not explained by patterns of foraging behavior, and are expected to confer individual-level benefits for participating males. Both the literature review and empirical study of umbrellabirds suggest that off-lek interactions and behavioral strategies may shape sexual selection processes at leks in important ways. Further research into this historically understudied area of lekking species' behavioral ecology will likely deepen our understanding of the evolutionary dynamics of lek mating. Lay Summary & BULL; Social behavior away from the lek may influence and interact with sexual selection processes in important ways, yet this component of lekking species' behavioral ecology remains very poorly known. & BULL; A synthetic literature review suggests considerable diversity in the form and degree of off-lek sociality among lekking birds, both within and between species. & BULL; Potential adaptive explanations for the function of off-lek sociality in a given species include foraging enhancement, predation avoidance, and mating benefits. & BULL; In Long-wattled Umbrellabirds, we find that the size and coordination of male off-lek groups increases during the mating season. This pattern is not observed in females and is not related to the proportion of fruit in the diet. & BULL; We suggest that off-lek sociality in umbrellabirds enables males to synchronize foraging and display periods, which is expected to confer individual-level reproductive benefits.

Automated summary

Lekking birds show variation in off-lek sociality, but this area has been understudied. This study provides a literature review and conceptual framework for understanding off-lek sociality in birds. It also presents evidence from the Long-wattled Umbrellabird that off-lek sociality in males is driven by reproductive incentives and benefits coordination during the breeding season. These findings suggest that off-lek interactions have important effects on sexual selection processes at leks.