This summer, we conducted our first pocket mouse translocation, the first of a member of the Perognathus family! In partnership with Eastern Water District, U.S. Fish and Wildlife Service, and Riverside County Parks, 43 San Bernardino kangaroo rats and 124 Los Angeles pocket mice were collected over 21 days in the San Jacinto River Basin. San Bernardino kangaroo rats are a subspecies of the Merriam’s kangaroo rat. Compared to Stephen’s kangaroo rats, they are smaller and lighter in color (especially on the bottom of their feet). However, their most distinguishing characteristic is that San Bernardino kangaroo rats (SBKR) have four hind toes, whereas other local kangaroo rat species, including the Stephen’s kangaroo rat, have five toes. Los Angeles pocket mice are similar in size to Pacific pocket mice; both average between 0.2 and 0.3 ounces (6 and 8 grams) in weight. However, Los Angeles pocket mice are slightly lighter in color.
All collected animals were placed in a holding facility at Skinner Lake Reserve. Luckily, it was the right time of the year for nature to take its course, and our captive populations quickly grew. These animals reproduce and grow rapidly, so many of the juveniles where already independent at release time. For instance, Los Angeles pocket mice are weaned at 22 days and are already sexually mature by 42 days old.
Translocation started with placing each animal in an acclimation burrow for one week. These are artificial burrows that are dug into the ground and caged off, allowing the kangaroo rats or pocket mice to become accustomed to their new home while being protected and fed before they have a chance to disperse. Ultimately, 65 SBKR and 144 Los Angeles pocket mice were translocated and released at a less-populated area of the San Jacinto riverbed east of the city of Hemet. Pocket mice and kangaroo rats were grouped into small neighbor groups based on their territory locations at the source site. Individuals were placed near potential mates and offspring, if they had them. Furthermore, the small groups (32) of pocket mice or (12) kangaroo rats were alternated in a grid pattern.
Last week, our SBKR team conducted the one-month post-release retrapping to check on who has survived and who has stuck around the release site. Of course we did not expect to find all of them, but we are happy to report that we found about one-third of each species. They look good and healthy; several females are already pregnant or lactating. For the next two months, our team will supplementally feed both species at their release site to help them become established. We will trap them again in October, three months after their release, to check on their status.
This project has been very exciting, as it could potentially provide us with valuable information for the future restoration of the endangered Pacific pocket mouse.
Christine Slocomb is a senior research technician at the San Diego Zoo Institute for Conservation Research. Read her previous post, Summer Pitfalls: Lots of Lizards!