Shady Pines: A Retirement Home for Mice

The Pacific Pocket Mouse (PPM) Conservation Breeding and Reintroduction Program marked its sixth year in 2018. Over the years, we have had a unique opportunity to learn about the behavior, genetics, and physiology of this amazing species! We have also had over 300 pups born at the facility, and have conducted multiple releases of captive born PPM into their native home range.

As San Diego Zoo Global’s Institute for Conservation Research is the only place in the world to house, breed, and release PPM, we are always asking new questions and adapting our practices to provide the best possible care and environment for the species.

A new challenge that became apparent this past year was the increasing age of some of our original mice. In the wild, the average PPM lifespan is 3 to 4 years; however, without predation pressure, resource limitations, competition, and exposure to the effects of climate change, the mice in our care are living longer.

We have mice in the facility over six years old, and needed to adapt our protocol to accommodate our new elderly community. 

The result was the creation of a retirement colony. Based on PPM life history and onset of reproductive senescence, we decided that mice four years or older, are unlikely to reproduce, and/or have genes present within the current active colony. They are eligible for retirement.

We affectionately refer to our retirement colony as Shady Pines, an ode to my favorite sitcom, The Golden Girls. For those not familiar with the show, there are four retired women living together: Dorothy and her mother Sophia, Blanche, and Rose. Female #26 is definitely the Dorothy of the group because she’s very smart and loves to snack; and male #72 is Blanche because of his enthusiasm in breeding trials. Female #20 is the Rose of our group because of her sweet nature, and #18 is the one and only Sophia of Shady Pines because she is the oldest!

While all PPM at the facility are optimally managed, there are some perks to being a resident of Shady Pines. Because these mice are not being considered for breeding trials or reintroduction, we are able to handle these mice less frequently. We can provide slightly larger cages, and as long as their weight stays above 6.0 g (approximately the weight of 3 pennies), and they are in good physical condition, they have access to a buffet of native seeds, finch seeds, sunflower seeds, and greens. 

The retirement home here at the facility is so popular that there is now a waiting list! In other words, we have more mice that are approaching retirement than we have room for in our designated Shady Pines room. Do not worry, though, the mice on the waiting list are still retired and receive all of the perks, but are waiting for a vacancy to be moved into the Shady Pines Room. 

Overall, the addition of Shady Pines to our facility has been very positive, and our retired mice love their Shady Pines community!