Wandering woodpeckers: foray behavior in a social bird

Abstract

In many cooperatively breeding taxa, nonbreeding subordinates, or helpers, use extra-territorial forays to discover dispersal opportunities. Such forays are considered energetically costly and foraying birds face aggression from conspecific members of the territories they visit. In contrast, breeders in cooperatively breeding taxa are expected to foray seldomly. We used novel tracking technologies to follow 62 acorn woodpeckers (Melanerpes formicivorus), a cooperatively breeding bird, to study extra-territorial foray behavior. Both helpers and breeders engaged in extra-territorial forays routinely and often several times per day. Helpers forayed earlier in the day and invested more time when foraying to high-quality territories. Unexpectedly, breeders forayed as often and as far as helpers. Breeders from high-quality territories forayed closer to their home territories than breeders from low-quality territories, reflecting a potential trade-off between foraying and territory defense. Such a routine pattern of extra-territorial forays in both helpers and breeders suggests that the motives behind forays differ by sex and social status and involve more than simply searching for dispersal opportunities.

Workflow for constructing social networks from automated telemetry systems

“…cooperative social groups (Koenig et al, 2016). We also found substantial associations between groups when individuals engaged in forays (Barve et al, 2020a) to other group territories (as evidenced by edges crossing territories in the network in the spatial layout (Fig. 4a), and by clustering of nodes of different colors when using a layout based on patterns of social connections (Fig.…”

“…Acorn woodpeckers track associations between individuals outside their social groups (Pardo et al, 2018;Pardo, Hayes, Walters, & Koenig, 2020), and both breeders and helpers make multiple extra-territorial forays almost daily. Foray distance can be over 4 km and individuals may spend several hours, or even days, on forays (Barve et al, 2020a). This suggests that the motives behind foray behavior may go beyond merely finding dispersal opportunities but may also include information-gathering and maintaining social associations with other birds in the extended social "neighborhood" (Barve et al, 2020a).…”

“…Foray distance can be over 4 km and individuals may spend several hours, or even days, on forays (Barve et al, 2020a). This suggests that the motives behind foray behavior may go beyond merely finding dispersal opportunities but may also include information-gathering and maintaining social associations with other birds in the extended social "neighborhood" (Barve et al, 2020a).…”

“…Automated telemetry typically generates large volumes of data based on proximity of individuals to base stations, thus significantly expanding the number of individuals that can be tracked, spatial extent of monitoring, and duration of data collection. Such automated telemetry systems have wide applications for monitoring vagile organisms, particularly for environments and contexts where direct observation is difficult (e.g., in marine environments [Finn et al, 2014], migratory species [Lefevre & Smith, 2020;Baldwin, Leap, Finn, & Smetzer, 2018;Bird Studies Canada, 2019], and for territorial organisms that live in spatially large and socially complex systems with substantial intra-day movement (Aplin et al, 2015;Barve et al, 2020a).…”

“…We use data from a 2-year automated telemetry study of social associations in a well-studied population of a cooperatively breeding bird, the acorn woodpecker (Melanerpes formicivorus). While these birds live in stable cooperatively breeding groups year-round, both breeders and helpers make multiple daily prospecting forays to other territories (Barve et al 2020a), and thus social associations occur both at home territories and during forays. We demonstrate that this approach allows one to parse out patterns of association across a variety of social (e.g., within a home territory vs. prospecting for breeding vacancies), temporal (e.g., across days or seasons), and spatial (e.g., at different territories spread over the study area) contexts.…”