Zebra finches program their offspring to prepare for global warming by singing to eggs before they hatch. In especially hot areas, finch parents make a special call to incubating eggs, basically telling them it’s really hot outside and they better not grow too big. The hatchlings listen — and this mechanism might explain how birds learn to adapt, and survive climate change.

Many bird species sing to their eggs. These calls have been shown to do everything from improving learning to synchronizing hatching times. When it comes to the Australian zebra finch, we already know that they make a specific call when it’s unusually hot outside, which in this case means over 79 degrees Fahrenheit no matter what season it is. Finch parents start making these calls about five days before the eggs are supposed to hatch and the calls become more frequent the closer it gets to hatch time. This suggests the calls are a way to tell the soon-to-be-born finches about the world outside, and not just the parents complaining about the heat.

Nestlings that heard the “heat” calls were smaller than the ones who didn’t

But how do we know if it’s just a coincidence? Mylene Mariette and Katherine Buchanan at Australia’s Deakin University figured out a way to test this. For a study published today in Science, they put a bunch of zebra finch eggs in an incubator that created a temperature around 100 degrees Fahrenheit. Mariette and Buchanan then played the “global warming” call for some of the eggs and not others.

Next, the scientists waited to see if there were significant differences between the two groups. If there were, it was probably because of the difference in the calls they heard.

After the eggs hatched, the baby finches were raised in an environment where the temperature varied naturally. By day 13 after hatching, nestlings that heard the “heat” calls were smaller than the ones who didn’t. This seems to confirm that the embryos in the eggs really do listen to the calls and then change how they grow.

All this makes sense because other research tells us that animals end up smaller when it gets hotter because the smaller size makes it easier to cope with high temperatures. Mariette and Buchanan also found that birds who were smaller in hot conditions produced more fledglings during their first breeding season, showing that this is a good evolutionary strategy after all.

In this case, at least, it’s a clearly good idea to listen to what the parents are saying. I imagine the lullaby goes something like this, in the spirit of the best Disney songs:

be a bird

you must be swift as a coursing river

be a bird

with all the force of a great typhoon

we a bird

with all the strength of a raging fire

but stay small or global warming will be our ruuuuin