The ecology of social foraging behavior in bats

Abstract

Both foraging and socializing have a profound influence on survival and reproductive success, and for many animals, are highly interdependent. Social foraging thus produces a vast and intriguing set of animal behaviors. In my doctoral thesis I investigated how ecology shapes social foraging behavior. The crux of social foraging is the balance between the costs of increased competition and the benefits of improved foraging success. This balance depends on a multitude of factors, but central is the distribution of resources exploited by animals. Food availability and predictability can fluctuate in space and time in various and complex ways, and determine when, where, and how social information can benefit the foraging success of animals. In the first chapter, we laid the groundwork for these investigations by reviewing the theoretical and empirical literature in social foraging in animals across taxa, focusing on cases involving patchy, ephemeral, and shareable food distributions. These conditions can render both active and passive information sharing adaptive. To address the extensive variation both in the behavioral patterns of animals using social information under these conditions, and in the distributions of food they experience, we developed a conceptual framework for characterizing the different foraging strategies of animals using social information. We determined that two critical elements, how long food persists in a given location and the relative benefit of using social information based on an animal's physiological and ecological state, predict when one strategy is more advantageous than another. We validated the framework with a systematic review of empirical studies on social foraging in bats, leveraging their diverse foraging niches and behavior to explore the implications of social foraging across different environmental contexts. For my second chapter, we further reviewed the literature on social foraging and information transfer in bats, focusing on the history of the field and how our understanding of the social lives of bats outside of the more well-studied roosting context has changed over time. Due to the cryptic lifestyle of bats, tracking technology has provided the only real insight into bat social foraging behavior. New technologies of the last decade have enabled researchers to gain unprecedented insight into bat behavior, in particular, group movements and sociality beyond communal roosts. Building on these advancements in the field, we explored these topics with two case studies in foraging bats that exploit food with different distributions, addressing key knowledge gaps identified by our framework. First, we quantified seasonal shifts in the unpredictable and ephemeral insect prey distribution of a neotropical bat species known to forage socially, and related this to changes in their foraging effort. We used modified camera traps to measure prey availability and miniaturized GPS loggers to characterize bat foraging effort, both at high temporal resolution. Insect abundance was lower in the wet season, rendering swarms more unpredictable and ephemeral, and correspondingly bats expended greater effort searching for them. Our results demonstrate the importance of quantifying prey distribution at fine-scales, concurrently with foraging behavior, and considering reproductive status or other physiological demands to make accurate conclusions about behavioral adaptations and plasticity. Second, we investigated whether foraging behavior of fruit bats that exploit heterogenous landscapes of mixed resource unpredictability and ephemerality is influenced by social associations. As colonial-living, central-place foragers, they face heightened competition for food, but may benefit from social information use. We deployed cutting-edge multi-sensor biologgers that collect synchronized GPS and proximity data on a large portion of a colony simultaneously, in a season of limited food quality. Despite only obtaining data for male bats, which are expected to be less social than females, we found that bats used patches at the same time as other tagged bats non-randomly and exhibited persistent social associations across roosting and foraging contexts. Our findings suggest that social connections, possibly facilitated by the sharing of foraging information, play a role in how these bats manage competition and coordination within their colonies. Furthermore, our results demonstrate that large-scale tracking can illuminate the social dynamics that underpin colonial-living. Overall, this dissertation advances our understanding of the ecological drivers of social foraging strategies by providing a conceptual framework coupled with empirical evidence from detailed case studies. It highlights the dynamic interplay between ecological conditions and social behaviors, enriching our knowledge of how sociality evolves and is maintained in bat populations. This work not only sheds light on the complexities of bat social foraging but also sets a precedent for studying social information use in other animal taxa facing similar ecological challenges.