Foraging games between gerbils and their predators: Seasonal changes in schedules of activity and apprehension

The interactions between predators and prey often constitute foraging games where prey manage risk and predators manage fear. Tools available to prey to manage risk include time allocation and apprehension. Such a game exists between gerbils and their predators in sandy habitats in the Negev Desert. Pulses of seeds made available daily by wind action result in a tightly choreographed game of changing seed availability and changing gerbil and predator behavior throughout the night. This outcome depends on summer conditions, especially the mobile sandy substrate that allows for daily renewal of resources. But winter conditions are far different: colder temperatures and wet, immobile substrate that stymies seed renewal. Here, we examined nightly patterns of rime allocation and apprehension in gerbils in summer and winter. Gerbils showed higher GUDs (giving-up density, a measure of time allocation) and higher selectivity for full resource patches over micropatches (a measure of apprehension) in winter than in summer. Also, gerbils showed stronger responses of GUDs to moon phase and time of night in the summer and stronger responses of selectivity to moon phase and microhabitat in the winter. In summer, gerbils use apprehension and, especially, time allocation to manage risk; in winter, gerbils rely more on apprehension. These results show how a forager's use of time allocation and apprehension depends on the nature of resource renewal and the cost of thermoregulation while foraging. Such factors can vary greatly across seasons and result in very different tactics for animals managing food and safety through foraging behavior.