Extreme Makeover:  Habitat Edition

If we build it, will the mini mice come?  That was the question we asked over the last year on our Pacific pocket mouse project.

Since the inception of our project in 2006, we have documented low numbers of this critically endangered mouse. So low, that we haven’t been able to take animals out from a source population to establish a new one (aka translocation). We have found low numbers of mice in pockets of coastal sage scrub habitat, characteristic of coastal California. We also have found them in young nonnative grasslands that thicken as they mature and exclude the mice and other small rodents from getting to their burrows in the bare ground.

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We set out to give the habitat a “makeover” to see if, in lieu of a translocation, pocket mice would reestablish themselves without our help. Last summer, we designed an experiment. We selected a site in an area that used to be home to these mice, but where they haven’t been captured over the last several years. The site was covered in invasive grasses but had some beautiful stands of white sage typical of coastal sage scrub communities.

We spent a week trapping all of the small mammals and then gave the site a makeover. On half of our sites, we went at the invasive grass with a weed whacker leaving native species unharmed. The other half we left untouched. 

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Six weeks after our habitat enhancement, we trapped again. We kept the invasive vegetation low over the winter and spring and retrapped a second time this past July. The good news: our enhancements worked. Small mice of other species do prefer enhanced habitat over control sites with thick grasses. But, our makeover wasn’t enough to bring the pacific pocket mice back.  We suspect that there are simply too few pacific pocket mice remaining in the area to rebound simply from a habitat enhancement. 

The take home message: re-establishing pacific pocket mice in areas with few mice remaining requires habitat restoration and supplementing the site with mice from somewhere else. 

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Where are we going to get more mice?  We are hoping to start a conservation breeding program for our mini mice off exhibit at the San Diego Zoo Safari Park in 2011. The plan is to start with a surrogate species, the Los Angeles pocket mouse. As a species of special concern in California, LAPM is also in need of some conservation attention. 

We intend to work out the methods for conservation breeding and reintroduction with LAPM and then to bring in a small number of pacific pocket mice in 2012. If all goes well, we hope to be reestablishing this critically endangered mouse at several sites through coastal southern California in the coming years.