Pre-dispersal movement patterns in non-breeding individuals of the cooperatively breeding Acorn Woodpecker (Melanerpes formicivorus)

Background/Question/Methods

Dispersal is an important life history stage for many organisms, but remains poorly understood, due primarily to the difficulty of studying the permanent relocation of organisms. Pre-dispersal movements, such as forays or floating, may be important information-gathering systems to inform dispersal decisions; in cooperatively dispersing species, pre-dispersal social interactions may predict dispersal coalitions. Tracking multiple individuals simultaneously with high temporal resolution, however, rapidly becomes cost-prohibitive using traditional radio telemetry systems, and modern GPS transmitters remain too large for many avian species. The cooperatively breeding acorn woodpecker (Melanerpes formicivorus) provides a model system with a well-documented social environment and a complex system of cooperative dispersal; recent advances in telemetry allow for the simultaneous tracking of many individuals, making questions regarding association of individuals more feasible to examine than ever before. Here we present the results of five months of continuous automated radio telemetry monitoring of eight non-breeding helper (pre-dispersal) acorn woodpeckers, using a novel solar-powered nanotag system. 

Results/Conclusions

Individual acorn woodpeckers exhibited highly variable movement patterns and extremely high rates of foray behavior, with most helpers spending over 90% of their time outside of their natal territories. Related same-sex helpers had more spatial and temporal overlap in main foray locations, whereas related opposite-sex helpers and unrelated individuals shared little overlap. One pair of male helpers, fledged from the same brood, exhibited spatial and temporal synchrony, indicating that the two individuals travelled as a social unit. This pattern suggests that cooperative dispersal coalitions may form previous to dispersal events and are involved in foray decisions. These results not only demonstrate the efficacy of the novel system but highlight the importance of social interactions in determining movement patterns among kin.