When forced to choose, some songbirds prefer the company of their mates to a good meal. Social living entails some compromise; that’s as true for birds as it is for people. Foraging in flocks often means that some birds get a little less food than they might by flying solo, but there is also safety in numbers: flocks provide better defense against predators and more eyes to watch for danger. For most, a little food for a lot of security is a worthwhile tradeoff. Some songbirds, it turns out, are willing to make even greater sacrifices for the sake of staying close to their mates. Great tits – small songbirds with yellow, black, and white feathers – seem perfectly willing to spend time at a feeder where they can’t get any food, in order to stay close to their mates who can eat there.
Oxford University zoologist Joshua Firth and his colleagues set up several high-tech bird feeders in the woods west of Oxford. At each feeder, a radio frequency identification (RFID) reader would open the feeder only for birds with the correctly coded RFID tag. Half of the readers in the area opened only for even-numbered tags, and half opened only for odd-numbered tags. Some mated pairs ended up with matching RFID tags, allowing the couple to forage together at the same feeders. Other couples weren’t so lucky; one partner got an even-numbered tag and the other got an odd-numbered tag. Birds in these conflicted couples had a choice: they could feed, or they could stay near their mates, but they couldn’t do both at the same time. When forced to choose, most birds chose to stay close to their mates. Birds in conflicted pairs visited feeders they couldn’t use 3.8 times more often than birds in compatible pairs – who, of course, had little reason to visit feeders other than the ones they could use.
Not So “Bird-Brained”
At first glance, that might seem like poor decision-making on the part of the birds. On the other hand, without a mate a bird can’t reproduce or raise chicks, so it’s easy to see why natural selection might favor birds who choose the long-term benefits of mating over the short-term benefits of more food. Other social relationships also provide important survival benefits. Zoologists have developed models that predict birds’ foraging behavior based on the idea that birds will opt for whatever gets them the most food for their time and effort. But this experiment may prompt some zoologist to rethink that model in favor of one that takes social relationships into account.
The Art of Compromise
Like many human couples, compromise among bird couples doesn’t always make immediate sense to outsiders. You might expect conflicted birds to split their time evenly between their feeders, so that both partners could get some feeding time in, but that wasn’t always the case. “Some birds would get away with mainly going to their preferred feeder, and having its partner following it there - the flipside of this of course is that it means some birds pretty much spent all of their time at a feeder they were not allowed access to, just because its partner was going there,” says Firth. “Interestingly, this doesn't seem to be strongly related to the sex of the birds.” Birds who humored their mates more often didn’t necessarily go hungry, however. Instead, they found a clever way to make the most of the situation. The feeders stayed open for a couple of seconds at a time, so by landing at a feeder quickly enough after their mates, birds could “scrounge” some food before the feeder closed. Firth and his colleagues say that partners even seemed to be deliberately helping each other scrounge. Firth and his colleagues published their findings in the journal Current Biology.
Birds of a Feather
Choosing to stick close to a mate influenced the birds’ other social relationships. Birds in compatible pairs mostly hung out with the same group of birds, or, in this case, those with matching tag codes. But birds in conflicted pairs spent more time with their partners’ flock: birds with opposite tag codes from their own. On average, birds in conflicted pairs only associated with their own flock about 49 percent of the time. That’s a familiar situation for many people. “Whilst I'd prefer to spend my Friday nights in a burger place with all my friends, I've actually spent quite a few at fancy restaurants, sitting with people I don't really know,” says Firth. “The reason I'm there is because my wife is there, so it's consoling to think even wild birds might end up in a non-preferred place with a particular set of other individuals because that's what their partner has decided on.” So for birds, as for humans, mate choice has a big impact on social networks, which in turn can affect how diseases and information spread through bird populations.
Photo credit: EtiAmmos/Shutterstock