Politics

The Great Tit Sacrifices Food to Be With Its Partner

Animals do the most amazing things. Read about them in this series by Janaki Lenin.

A great tit. Credit: Keith McMahon

A great tit. Credit: Keith McMahon

Great tits, sparrow-sized European birds, spend most of their waking hours looking for food. This tendency to follow their stomachs is even more important in winter, in the weeks preceding nesting. Breeding takes a lot out of these small birds. They lay up to 12 eggs, keep them warm, and then cater to the growing demands of chicks until they fledge. Parents have to be in fine form to withstand these rigours. Single parenthood is not an option. The strong bond between parents sees them through the tough time.

Scientists from the University of Oxford, and University of Konstanz, Germany, put the birds to the test to see which of these needs outweighs the other: food or mate.

In the Wytham Woods, west of Oxford, U.K., great tits feed at feeders set by humans. Scientists fitted 17 pairs of great tits with radio-identification tags, also known as PIT tags.

“They are mini, lightweight, cheap, and power-free tags that can be detected as the individual animal comes within range of a reading station,” says Joshua Firth, the lead author of the study. “This allows us to track great tits through their whole life. By deploying PIT-tag detecting feeding stations throughout Wytham Woods, we have over 12 million detections of over 4000 great tits.”

Firth and his team connected the doors of the feeding stations with PIT tag readers that recognise each bird’s unique tag number. They programmed half the readers to open the feeding stations for birds wearing odd-numbered tags, and the other half to open for birds wearing even-numbered tags.

If both the male and female of a pair had the same type of tags, they didn’t have to decide. They fed together at an accessible feeder. Other pairs were not so lucky. Where the male could feed, the female was prohibited, and where the female could feed, the male was barred. So what would the starving birds do?

Would they heed the rumbles of their empty stomachs and abandon their mates? Or, would they rather starve and consort with their partners that are busy stuffing themselves? For great tits, both must be important. But when faced with a dilemma, how would they decide?

Animals are expected to be where they can access resources, especially food, says Firth. And they hang out with others who share the same area. This is a general theory in behavioural ecology.

Since birds are simple creatures, one would expect the demands of filling their bellies would be more immediate than bonding with their mates.

However, the great tits surprised the scientists. Instead of going to another feeder where they could hog, the birds opted to go hungry and stay with their mates.

Did the pairs always frequent the same feeder? Did males follow the females?

“It was actually quite variable what they did,” says Firth. “In some cases, it was a fairly even split between which feeders they went to. In others it was dominated by one bird mainly going to their preferred feeder and the other one following it there. Interestingly, this doesn’t seem to be strongly related to the sex of the birds, and more to do with the individual pairs themselves. In future work, it’d be great to test what causes some individual birds to take control and dominate the decisions of the pair to suit their own needs.”

The researchers suggest mates are a resource, just like food. Doing their utmost to keep the bond with their mates strong is their only ticket to success as parents. The birds sacrifice their short-term needs for long-term profitability.

“Therefore, even in wild animals, an individual’s behaviour can be governed by aiming to accommodate the needs of those they are socially attached to,” says Firth.

Another study published in 1989 also came to a similar conclusion. Ruth Mace, the author of that paper, performed the experiment in May in the midst of nesting. This is a time when males preferred to be with their mates than feed. They were guarding them, making sure they didn’t mate with other males.

Firth describes how the two studies differ. “I did not focus on mate guarding behaviour during the females’ fertile period. A male may choose immediate mating opportunities, rather than the maintenance of a relationship itself. We hope that our work, done when males and females are not breeding, may be widely applicable to all kinds of different relationships, rather than those driven by copulations.”

By accommodating their partners’ needs, the birds let themselves in for other changes, such as their social network.

“Our previous study published earlier this year showed that manipulating where individuals could access resources did indeed change who their flock-mates were,” says Firth.

Under normal circumstances, birds would feed at the feeders with their buddies. Hungry birds consorting with their mates also spend time with others who don’t belong to their normal flock. By associating with a cohort of strangers, these birds build new social relationships.

The great tits had another surprise in store. The devoted birds that stayed close to their partners didn’t starve to death.

Not for nothing are great tits known for their problem-solving skills. The enterprising birds observed that the feeders’ locking mechanism was delayed by two seconds. As soon as their partner got seeds and moved off, they too snuck food out of the feeder before it locked itself again.

“Interestingly, a relatively large amount of this scrounging was enabled by the bird’s own partner unlocking the feeding station, suggesting it may be a cooperative strategy,” says Firth.

Over the three-month experiment, the birds grew more proficient at the technique. What’s remarkable about this study isn’t that birds gave up food to stay with their mates. They recognised their mates were hungry and helped them access food. That’s true pair bonding.

The study was published in the journal Current Biology on 12 November 12, 2015.

Janaki Lenin is the author of My Husband and Other Animals. She lives in a forest with snake-man Rom Whitaker and tweets at @janakilenin.