Male Pacific pocket mice in the wild emerge from their winter burrows somewhere between February and April, and females follow suit about two weeks later. Almost immediately, we see the first matings of the year. We were hoping for the same in our new captive colony…if we provided the “correct” captive environment, anyway. If you have been following my previous posts (see Pocket Mice Arrive), you know that we brought the first Pacific pocket mice founders in from the wild last summer. We were surprised but thrilled to have a female go into estrus in January. The start of her reproductive cycling meant that at least one of the females found the captive environment suitable ☺.
This spring, a few females have come into estrus, and while no fights occurred during pairings with males, neither did matings. Females #9 and #13 were in estrus Saturday night. We waited until just after sunset and started the night by pairing Female #9 with four different males. Male after male there was no aggressive behavior, but Female #9 avoided each suitor. As similar to other species, female pocket mice prefer males that are interested but patient, persistent but not aggressive. Sound familiar? Males #21 and #25 were doing all the right things. In fact, I was so impressed with Male #25’s “moves” that I decided to try a pairing with him and Female #13.
I was crossing my fingers anticipating the first interaction. Female #13 came out of her tube first and started sand bathing. Male #25 emerged about a minute later. They approached each other a couple of times and then immediately began following each other in a tight circle. They were moving so fast that they looked like a spinning pinwheel with their little tails flying behind them. After only 30 seconds, they were mating. SUCCESS! The whole event was over in about eight minutes, and the next time the male approached the female, she tried to bite him on the head and ran away. It was clearly time for me to separate the pair.
This was the first mating of Pacific pocket mice in captivity! I left the facility at the San Diego Zoo Safari Park that night exhausted but thrilled.
We have moved #13 into a larger cage and changed her diet to support pregnancy, though we won’t know for a week or two if she is pregnant. Gestation for this species lasts about 22 days, so we are hoping to have little ones around June 9.
Debra Shier, Ph.D. is the San Diego Zoo Institute for Conservation Research Brown Endowed Scientist.