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Foraging Decision Making in the Real World – revealed from a bat’s point of view by on-board miniature sensors

Periodic Reporting for period 4 - GPS-Bat (Foraging Decision Making in the Real World – revealed from a bat’s point of view by on-board miniature sensors)

Reporting period: 2020-09-01 to 2021-07-31

Animals must make crucial decisions during their lifetime. The most common decisions that animals make are foraging decisions. Many species must decide where to forage and how to get there on a daily basis. Despite the immense importance of foraging, our understanding of how animals make foraging decisions under natural conditions is very limited. A major obstacle hindering our ability to study decision processes in the wild is lack of data. Studying decision-making in the field is extremely challenging, because it requires not only monitoring an animal’s movement, but also monitoring its foraging and its interactions with other individuals. This becomes extremely difficult when studying a small animal like a lizard, a song-bird or a bat. The main goal of this ERC project is to develop methods to bridge this knowledge gap and to use these methods to study several fundamental aspects of foraging decision-making, using bats as models.
Our environment is changing today more rapidly than ever, mostly due to human activity. Most animals suffer from this situation; many do not survive it. Only a better understanding of how animals behave in their natural environment, and of their basic needs, will allow developing conservation plans to help them survive. There are numerous examples of conservation plans that failed because of a lack of understanding of the species actual needs.
The first step toward reaching our goal was technological – we aimed to develop miniature tags that can be mounted even on small bats and include several sensors: GPS, accelerometers that allow inferring different behaviors such as flying vs. hanging and a microphone that allows monitoring foraging and interactions with other bats based on recording sound and specifically bat-echolocation. This step has been completed, and we are now using these new tags to study foraging decision-making focusing on four main questions (Work Packages):
1) Social decision-making (in fruitbats) - how does living in a colony assist foraging.
2) Spatial decision-making - we aim to compare the movement and behavior of bats that rely on predictable food, like fruit, and bats that rely on unpredictable food like insects.
3) Flexible decision-making – how animals change their decisions when original decisions turn out to be wrong.
4) Developing a computational frame-work that can explain some of these aspects of decision making.
We achieved many of the goals mentioned in the original proposal. On the technological level, we completed the development of a miniature multi-sensory tracking device. In WP1 we established an in-house open fruit-bat colony which allowed us to look at bat sociality and navigation in addition to examining the effects of the environment on foraging. In WPs 2-3, we collected vast data on two very different bat species – a social forager and an individualist. This led to writing a paper comparing five different species revealing that resource ephemerality drives sociality while foraging. Finally, WP4 aimed to model foraging decision making. We generated several models along the years of the project and we are currently working on integrating them into one model.
Our main results were:
WP1. We established an open bat colony where bats are free to fly in an out. This allowed us to track the same bats over up to six months, revealing that new-born bats map their environment based on visual input and can perform short-cuts. We demonstrate that they can perform map-based navigation (Harten et al. Science 2020). We moreover describe the complexity of the social structure of the fruit-bat colony including long-term interactions between its individuals (Harten et al. 2019 Current Biology).
WP2-3. We revealed that bats that rely on an ephemeral resource such as swarming insects or flocking fish search for food collectively in order to improve foraging while bats that rely on food whose location is known such as fruit bat search for food individually. We further find that insectivorous bats that rely on reliable patches of insects will also forage individually and will probably defend their foraging sites (Egert-berg et al. 2018 Current Biology).
In a spin-off on the main project we research sensory decision making in several bat species. We demonstrate that bats weight vision and echolocation when making classification and orientation decisions. We show how sensory cohesion is required for object perceptions (Danilovich et al. 2020 PNAS).
We were the first to track micro-bats using GPS and we were have tracked the smallest animal ever tracked using GPS. In that sense the project could clearly be considered as ground-breaking. Some of our results advanced the field beyond the previous state-of-the-art. For example, by comparing five different bats species across the world and by using a combination of field data and modelling we show how resource ephemerality drives foraging sociality. Our establishment of an in-house colony allowed us to track the same bats from birth to adulthood also going beyond the current state-of-the-art. This resulted in several findings including the first strong proof for real-life cognitive maps in wild mammals. Notably, our research allows examining decision making at the individual level in the wild, which has always been extremely difficult to do.
Colony of greater mouse-eared bats. (c) S. Greif