The mother goat's floppy ears perk up. From across the field, she hears one of her kids—not the new baby that's still nursing, but the grown-up kid who's packed up and moved to a different pen. Even though she no longer sees or feeds her older offspring, she'd know that bleat anywhere.
It's hard to know how well animals recognize and remember each other's voices; you have to follow groups of animals around for long stretches and keep track of how recently they've seen each other. Yet we have a few answers already. An Australian sea lion remembers its mother's voice for years after it's left her side. Cotton-top tamarins recognize relatives' calls even when they haven't seen them for several years. African elephants have been shown to remember a former group member's voice 12 years later.
Domestic goats are good subjects for this area of research: they're chatty, they're easy to find from one year to the next (since they live in pens), and they form close relationships between mother and kid. So researchers in the UK, led by Elodie Briefer at Queen Mary University of London, went to a Nottinghamshire farm to study vocal recognition among a small group of goat mothers.
The scientists recorded baby goats' bleating when they were five weeks old. Then they played back those recordings to the mothers while the kids were away from them. The mother goats' reactions—how much they bleated, how quickly they looked toward the source of the sound—were measured as a baseline.
More than a year later, the researchers brought their speakers back to the farm. By now, the goat kids they'd recorded had been weaned from their mothers for at least seven months. Mother and kid were living in separate pens where they couldn't see or hear each other. Meanwhile, another year's batch of babies had been born, and the mothers were busy nursing their new kids.
The scientists played the old recordings of their kids to the mother goats. But this time they were mixed in with recordings from other, unrelated goat kids that currently shared their pen. Would the moms be able to pick out the voices of their now-adult children from the other familiar bleating?
The mother goats didn't disappoint. They reacted more strongly to the sounds of their own offspring than to the sounds of the neighborhood kids. Acoustic analysis of the recordings showed that the moms weren't just mistaking the voices of their older kids for the similar sound of their younger kids. The goats had distinct voices, and their moms recognized them even when after they'd grown up and moved out.
If the mothers still reacted strongly to the recordings made when their kids were five weeks old, the authors reason, they've probably stored memories of their kids' voices throughout childhood. They may be able to recognize their offspring for many years afterward. (It would be nice to see the experiment repeated with new recordings of the adult offspring, though, so we'd be sure that the moms can still recognize their grown kids once they have more mature voices.)
Assuming mother goats can recognize their kids throughout life, there are some advantages. Goats are social animals, for one thing, so keeping track of each other is important. And there's a less cute reason to remember which animals are your offspring: Inbreeding avoidance, which is biologists' way of saying "not mating with your relatives." Kids sure do grow up fast.
Briefer EF, Padilla de la Torre M, & McElligott AG (2012). Mother goats do not forget their kids' calls. Proceedings. Biological sciences / The Royal Society PMID: 22719031