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.