This goes in the “just when you think you’ve seen everything” category.
One morning as Animal Caretaker Maida Ingalls prepared for her day, the early shift custodian pointed out to her that one of the naked mole-rats had escaped. This occasionally happens. A mole-rat will get out of the system of tubes and chambers, and wander aimlessly around the interior of their enclosure.
In this case, something much more dramatic had happened. The animal was spotted on the ground in front of the exhibit.
Maida quickly put him back and briefly recorded the escapee information. At first she couldn’t figure out how he got on the floor, but was able to deduce that he must have crawled between the doors and the sill, and then slid down the signs in front of the exhibit. Quite a feat for such a small animal! Surely the experience would dampen his enthusiasm for travel!
Not quite. Two days later, the same individual performed the same escape. This time there was a difference. While in his first escape, he had pushed one of the tubes out of a chamber, this time there was no visible means of escape. We did notice that one of the latrine chambers was filled especially high with bedding, almost to the very top of it. We believe he must have climbed the bedding and pushed the lid open to crawl out. So we taped down all of the chamber lids, hoping to prevent another escape. The offending mole-rat was marked with a black pen on the leg and observed for signs of trauma, then returned to the colony.
Only to escape yet again! During a cleaning later in the week, a new latrine chamber was installed without tape on the lid. Our perceptive mole-rat figured this out, filled the chamber with bedding and climbed out the top one more time. This time, when he reached the ground level, he climbed through a ventilation damper into the area below the exhibit, which could have been extremely dangerous if we hadn’t found him soon after. What was this hairless Houdini up to? Did he have a death wish?
Interestingly enough, this behavior has been described in other colonies as well, and it doesn’t appear to be entirely suicidal. This mole-rat is presumed to be a disperser morph – an individual within a eusocial group that is driven to carry its genetic material out of the colony of origin and found a new colony or integrate into an existing one. In the stable, well fed colonies kept in captivity, the disperser is usually a male, but in the wild males and females seem to become dispersers in about equal numbers.
The disperser might be thought of as a high risk, high reward behavior. The chances of survival in the wild for a solo mole-rat are slim. But any disperser hardy enough to stay alive and lucky enough to attract a partner is far more likely to produce offspring than he or she would be by remaining at home as a worker. To an animal living in an established colony, the pathways to breeding involve fighting – either with an established breeding animal, or with other contenders if the queen or her mate die. As founder of a new colony, the disperser would have ample opportunity to produce his or her own offspring rather than caring for those of others.
If our Houdini is a disperser mole-rat, his behavior is powerfully motivated and may continue. We are testing husbandry techniques to see whether high levels of enrichment will meet his dispersing need. If he is isolated from the colony, will he work to get back in? Or is getting away the whole point? Eventually, he may need to become a founder of his own, or join another organization’s colony, perhaps as a breeder. In the mean time, this peculiar behavior offers us yet another glimpse into the many adaptations of this eccentric species.
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