The study, published in the Biological Journal of Linnean Study, focused on zebra finches, a small species who form life-long pairs. Unlike elsewhere in the animal kingdom, male and female zebra finches share parental duties equally -- from nest-building to watching eggs and chicks. They even take it in turns to incubate their eggs, with one partner sitting on their eggs and one partner foraging at any one time.
Researchers observed 12 male-female pairs of zebra finches in an aviary. While the male of each pair was foraging, researchers trapped them for around an hour, delaying their return to the nest. When they returned within the normal time period, the two birds engaged in normal exchanges. But when the male was delayed, this exchange was "accelerated", with normal calls made much more rapidly.
The researchers also found that the time females spend away from the nest was not dependent on the time her partner was away in her previous shift incubating the eggs, but on how much he squawked when he returned -- males who called lots of times, rather than just a few, were rewarded with a swiftly returning mate.
Researchers say that this indicates that birds are not so different from humans -- rather than approaching parenthood 'tit for tat', they actually communicate just like us.