Caching by urban squirrels as a link between research and education

Background/Question/Methods Urban ecology provides an opportunity for engaging middle school, high school, and college students in outdoor ecology labs with wildlife.  In much of the United States, gray and fox squirrels are the most conspicuous members of the urban game park. They are scatter hoarders burying their caches across their home range.  The concept involves the value of caching to the squirrel, and the consequence of caching for seed dispersal. How far are seeds dispersed? Are seeds dispersed to certain areas more than others? How long does it take for squirrels to discover the seeds? Are some seeds consumed, or are all buried? What proportion of seeds is buried away from the release point? What is the difference in fate between seeds dispersed close to the release point compared to those dispersed farther?  We present here an easy methodology that can be used in public parks, private yards, schoolyards or campus gardens, to study seed dispersal by squirrels in an urban environment.  The method consists of attaching nylon spools of threat to hazelnuts with epoxy.  The spool is anchored in a plastic container (such as a plastic film canister) that can be buried into the ground.  The hazelnut resides on top of the lid.  The squirrels, upon finding the nuts, can collect, eat or hide them away.  As the squirrel moves the nut, the spool remains anchored in the container, and the thread plays out.  Students can track and monitor the caching behavior of squirrels by following the threads from the release point to where the squirrels either consume (shell fragments) or bury the nuts.  Students can further monitor cached nuts for consumption, and secondary dispersal as nuts may be recovered, and moved yet again within days of caching.  Results/Conclusions In several trials of this exercise, it took the squirrels from 24 to 48 hours to find and remove the hazelnuts. Of the 200 nuts released, 3% were consumed immediately, and the remainder buried individually as a widely dispersed scatter hoard.  Seventy two percent of the cached nuts were buried within 25 m from the release point. The numbers of seed buried decreased with distance.  Four nuts were found at greater than 55 m from the release point. The resulting exercise allowed college students to learn about seed dispersal, and promoted critical thinking to understand how squirrels can potentially help plants re-colonize areas within the human-dominated landscape.