Trilobites: How Dwarf Mongooses Respond to New Immigrants
Dwarf mongooses, the African social mammals that are cousins to the ever popular meerkats, are not actually people. And new research about migration from one mongoose group to another has nothing to do with the current world political situation.
It’s necessary to make this point because the temptation to anthropomorphize these creatures is extreme.
For instance, the basic conclusion of a recent study is that immigrants to a new mongoose group don’t contribute a lot at first, and are not given much credit when they try. But after about five months, they do just as well as any other mongoose.
Stop right there. Repeat after me: Dwarf mongooses are not people. They do not live in large nations torn by political differences over how to treat their borders.
They are small predators that live in groups of a dozen or less, foraging for food like scorpions and insects. They are killed and eaten by snakes and birds and bigger mammals. In any group only one dominant pair gets to reproduce. And immigration in the terms of the study consists of the movement of one mongoose from one group to another.
Julie M. Kern and Andrew N. Radford at the University of Bristol study social communication and they wanted to know how new mongooses functioned as sentinels and how the information they conveyed while on sentinel duty was received by the rest of the group.
So they monitored their behavior, how often they stood guard emitting a surveillance call that means, “I’m on duty here. ”
New arrivals generally did less sentinel duty than long-term group members, perhaps because of the physical drain of immigration. It may take several months for a mongoose that leaves its group to find another group that will accept it.
The researchers, or, actually the 24 research assistants that the researchers make a point of thanking in their paper in Current Biology, observed the South African mongooses and gathered data over several years. They also recorded and played back surveillance calls from different mongooses to judge how the other mongooses responded.
The reaction of group members was different and changed over time. And at first foragers did not show a lot of confidence in immigrants. They would stay vigilant when foraging, looking up frequently to check their surroundings. If a known group member was sending out surveillance calls, however, foragers were more relaxed, keeping their head down.
Even among well-known sentinels there were differences, Dr. Kern said. The members of the dominant pair were much more trusted than other mongooses.
However, by the time five months had passed the immigrants were trusted just as much as any other group member.
The reason that mongooses bother to switch groups, said Dr. Kern, is to get a better chance at reproduction. “If you’re quite far down the hierarchy in one group,” she said, “you may try to join a group that has fewer individuals of your sex.” Then you have a better chance of one day becoming one of the dominant pair.
The biggest threat to reaching a position of dominance is predation. That is to say, being eaten before you get a chance to reproduce.
The findings show that mongooses don’t just take a sentinel’s call at face value. They know who is making the surveillance signal and they consider the source. A dominant group member on duty makes them more relaxed. A new immigrant on duty is not as reassuring.
The comparisons, of course, are tempting. How long before we trust the new arrivals? But, really, these are mongooses, and they are reacting to one new arrival at a time. About the only conclusion that applies to both mongooses and people is that all social animals must cope with new members joining the group. What’s at stake and how the groups deal with it depends n all sorts of factors, not least of which is the nature of the social animal.
Anyone want a bite of this scorpion?