Nests are not for sleep. They are for babies. Flickr/Anna Hesser, CC BY-SA

Curious Kids is a series for children. If you have a question you’d like an expert to answer, send it to curiouskids@theconversation.edu.au You might also like the podcast Imagine This, a co-production between ABC KIDS listen and The Conversation, based on Curious Kids.

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I would like to find out something about swallows: we have noticed that they return to the same nests each year, but there must be younger birds that have no nest. Where do they sleep until they have built their new nest? – Nefeli, age 13, Corfu, Greece.

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Thank you for your question, Nefeli.

It’s true that some swallows return to the same nests each year. But what do they do there?

We need to understand what nests are really for – and they are not for sleeping. They are for putting eggs into. The eggs need protection from the weather (hot and cold, wind and rain) and from other animals that would eat them. For predators, eggs taste great!

Adult swallows must build their nests away from predators and unsafe weather conditions, such as the wind, heat and cold. merec0/flickr, CC BY-NC

Eventually the eggs hatch, then a blind and featherless baby swallow emerges. The babies are called nestlings or sometimes chicks. So nests are not for sleeping, they are for raising a family.

The babies that hatch from the swallow’s eggs are called nestlings or chicks. Rafael V/flickr, CC BY-NC

It is true that when an adult is sitting on eggs and nestlings, it may sleep, especially at night.

But the young swallows who don’t have a nest to return to must build their own nest (to protect and feed their babies) or sleep on a tree branch, a rock ledge of a cliff face, or inside the hollow of a tree.

When swallows sleep away from the nest they sleep in places called roosts.

So remember: nests are mostly for babies; roosts are for sleep.

A swallow might sleep in a tree. Flickr/Corine Bliek, CC BY

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Read more: Curious Kids: is water blue or is it just reflecting off the sky?

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Hello, curious kids! Have you got a question you’d like an expert to answer? Ask an adult to send your question to curiouskids@theconversation.edu.au Please tell us your name, age and which city you live in. We won’t be able to answer every question but we will do our best.

Graham Fulton does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.