I am happy to report that we had another successful (and exciting!) field season. We re-trapped endangered Stephens’ kangaroo rats (SKRs) on sites where they were translocated in 2008, 2009, and 2010. Fortunately, these SKR populations continue to grow. We tagged hundreds of new individuals! In addition, we moved 100 SKRs from human-impacted habitat onto the Southwestern Riverside County Multispecies Reserve. Each year, our team seeks to improve the success of SKR translocations by conducting field experiments. Since the best measurement of “success” is survival, our goal this year was to try to minimize predation in order to enhance survival. Basically, we wanted to keep SKR predators (coyotes and barn owls) off sites following an SKR release. It sounds easy, right? But as field biologists know, nothing is ever easy.
In 2008, we protected the translocated kangaroo rats from coyotes by putting an electric fence around the site. Unfortunately, the electric fence posts served as opportune perches for barn owls. In 2009, Scientist Debra Shier decided to try a different approach. She used scent and sound from the top predators (mountain lions and great-horned owls) to deter the mesopredators (coyotes and barn owls). Her results from these pilot studies suggested that there were positive effects for SKRs (see Mountain Lions Help Kangaroo Rats?), so this year we replicated these experiments at multiple release sites.
During this year’s SKR translocations, we put out mountain lion urine to deter coyotes (see A Summer Spent Helping Kangaroo Rats) at two of our release sites and used water as a control at two other sites. In order to deter barn owls, we played great-horned owl calls. We played the common poorwill’s call at our control sites.
We tracked coyote visitation using 32 remote cameras that surround our sites. In order to quantify barn owl visitation, we sat along the periphery of sites and listened for owl calls and observed them using night-vision goggles and spotlights. For a month, we monitored the sites as well as observed the kangaroo rats’ behavior. We wanted to better understand SKR behavioral responses following translocation.
You might think that sitting quietly in the dark with night-vision goggles for several hours would be boring. But it is actually relaxing (especially on clear, starry nights) and really exciting once the SKRs emerge from their burrows and begin hopping around, foraging, and chasing each other. We became members of the nocturnal world and were able to catch glimpses of various species including skunks, deer, and bobcats.
Our remote cameras will remain out at the release sites for three months to continue to provide us with images of any visitors, so make sure to check out our pictures on San Diego Zoo Global’s Facebook page. Once all of the data is in, we will determine if our treatments deterred predators. We will keep you posted!
Maryke Swartz is a senior research technician for the San Diego Zoo Institute for Conservation Research. Read her previous post, Where are Translocated Kangaroo Rats Now?