The Surprisingly Specific Conditions Robins Need to Nest

Not only is temperature a factor, but the picky birds also take into account humidity levels. Here's why.

This audio story is brought to you by BirdNote, a partner of The National Audubon Society. BirdNote episodes air daily on public radio stations nationwide.


This is BirdNote.

When we look for robins in spring and early summer, we often see them with their beaks full of earthworms. That tasty payload tells us a couple of things. For one thing, there’s a nest full of baby birds nearby, waiting for their next meal. But that beakful of worms is also a clue about the conditions in which robins choose to nest.

It turns out that robins are pretty choosy about this. When scientists looked at climate data for over 8500 robins’ nests in many parts of the US, they found that temperature is important: robins will nest only if the mean noon temperature is between 45 and 65 degrees. But even more critical is relative humidity: it needs to be right around 50 percent in the middle of the day. And if it isn’t, the birds will hold off.

What’s so special about this combination of temperature and humidity? It's the sweet spot when soft invertebrates move up near the surface of the soil. Like earthworms. Essential fuel for hungry nestlings. As for exactly how robins sense when the humidity is 50 percent — that's still an open question.

For BirdNote, I’m Michael Stein.



Written by Bob Sundstrom

Producer: John Kessler

Executive Producer: Dominic Black

Bird sounds provided by The Macaulay Library of Natural Sounds at the Cornell Lab of Ornithology, Ithaca, New York. American Robin song [168300] recorded by W L Hershberger; American Robin call [133356] recorded by G A Keller. 
BirdNote’s theme music was composed and played by Nancy Rumbel and John Kessler.

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June 2017  ID#  AMRO-13-2015-06-04 AMRO-13