Robert Fisher began surveying reptiles in the coastal sage scrub at the San Diego Zoo Safari Park Reserve in 1995 as a graduate thesis project. The Applied Animal Ecology Department of the San Diego Zoo Institute for Conservation Research, in partnership with the U.S. Geological Survey, has continued monitoring the biological diversity of the Safari Park Reserve since 2002. For one week a month, three seasons a year, the small mammals, amphibians, and herptofauna of the coastal sage scrub are surveyed by capture and release via pit-fall trapping arrays at 20 sites.
Each morning we visit every site to check every trap, identify each species, determine sex, and identify the age group. We then take a series of measurements on each individual including weight, tail length, body length, or even hind foot or ear length for mammals. Some measurements aid us in identifying some of the mammal species while others allow us to determine the sex of a snake. In the ever-changing mosaic environment of the coastal sage scrub, with rainy years followed by years of drought, or even fires that have changed the landscape, this monitoring project provides significant insights into the population ecology of the native species of the Safari Park Reserve.
After months of seeing many California voles due to the rainy year, we only saw four this month. Voles are a species classically studied because they “boom” and “bust” in their population sizes. Voles increase in number rapidly when resources are plentiful but quickly decrease once their resources have dried up. However, during their period of boom, California voles provide a valuable food source to the many predators that eat them, including hawks, snakes, coyotes, and owls. Overall, small mammals were few this warm month, with gray shrews and western harvest mice being the most common.
June was definitely the month of the orange-throated whiptail! We collected data on 119 individuals, including many that we have collected before. The males are out in their beautiful breeding orange, and we observed several pregnant females or females with spur marks from breeding. I even had one bucket trap that contained four males and one female. We might start to see some orange-throated whiptail hatchlings next month! Unfortunately, these lizards are listed as a species of concern by the California Department of Fish and Game, because they only remain on 25 percent of their historic range due to habitat destruction. This month does mark the start of this year’s hatchlings! So far we have processed side-blotch lizard, western fence lizard, and western skink hatchlings. Besides the orange-throated whiptails, we have seen some large and gorgeous western whiptails as well.
The snakes sighted this month were all exciting species. We found two kingsnakes, two California black-headed snakes, and one coast patch-nosed snake. The kingsnakes, though common, are unique in that the San Diego variety can be either striped (as were the snakes found this month) or banded, which is the more common pattern. California black-headed snakes are exciting to find due to the relative rarity of sighting one. They are a small species and often hide under and around rocks so are seldom seen, though they are a relatively common snake to catch in the traps. As for the coast patch-nosed snake, it is a particular favorite of mine due to the fact that it is a truly adorable species (and how often can you say that about a snake?). On top of that, it is exciting to find, since it is officially considered to be a protected species due to habitat loss. The fact that we see the patch-nosed snake at all shows, in my opinion, how wonderful it is that the San Diego Zoo has such a habitable reserve for such a variety of species.
Christine Slocomb is a research technician at the San Diego Zoo Institute for Conservation Research. Elizabeth Davis is a conservation education technician at the Institute.