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How much sleep does a bird need, and do they ever roost during the daytime in Summer with daylight hours being so long?

Sent in by John Newton, Liverpool

A good question. I don't think if anyone fully knows how much sleep a bird actually needs for healthy existence, since the amount of sleep they get is very variable. Sleep is something birds do when there either is nothing 'better' to do, or when darkness prevents other activity, importantly feeding. Its function is to save energy.

Most birds perch horizontally when they are sleeping, but some, such as treecreepers and woodpeckers, choose a vertical position on a tree trunk. Swifts sleep on the wing high up in the sky. Most curiously, parrots in the group Loriculus hang upside down like bats!

When birds sleep/roost and how long they do so does vary with the type of the bird you are looking at. Most birds in the UK are daytime birds, which carry out all their activities during the daylight hours, and rest/sleep at night since they need to see their food, and their eyes are not adapted to function so well in the darkness. If these birds have spare time during the day, they can sleep for short periods even in the middle of the day.

Owls, on the other hand, reverse this process, being active at night hunting small rodents that are also active then, and spend the daylight hours resting and conserving energy. At the height of the summer many owls end up hunting even in daylight, as the night is too short for them to catch enough food for themselves and their growing brood.

Many waders have yet a different pattern of activity. These birds feed on coastal areas, looking for small animals in the mud and shallow waters of estuaries and open shore. They have better eyesight in low light than our daytime birds have, and they feed by touch rather than by sight. Since their food only becomes available to them when the tide is out, they have adapted to be active and feed at low tide, and rest and sleep at high tide, regardless of whether it is day or night.

Many species of birds that nest in the UK also nest further north, right up to and beyond the Arctic Circle, where the sun does not set at all during the summer. These birds tend to have periods of rest, possibly sleep, either at a certain time during the 24 hour cycle, or in short periods at different times of the day. The overall length of time they spend sleeping tends to be a fraction of the time at more southerly latitudes where it gets dark at night.

Researchers consider this behaviour evidence that birds do not need much sleep at all, but are forced to do so in some habitats by the 'inconvenience' of darkness that limits their ability to carry out other behaviours for part of each 24 hour period. This may explain why birds like robins are reported so regularly singing at night close to a streetlamp or another source of light during the winter months.

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