Sleep deprived birds have more chicks

Mating For pectoral sandpipers, losing sleep means gaining offspring

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Sleep deprived birds appear to have greater mating success, according to a study conducted in Alaska.

By analysing sleep patterns and testing the paternity of chicks, a team of researchers from Germany and Switzerland have found that male individuals that sleep less, sire the most offspring.

This is at odds with the assumption that sleep loss retards the ability to perform complex tasks.

The research is published in Science.

Out all night

The birds studied were pectoral sandpipers (Calidris melanotos), which engage in long migrations between the Southern and Northern hemispheres.

In May and June, the shorebirds mate and nest on the barren tundra of Alaska, when the area experiences almost 24 hours of sunlight.

During fieldwork near Barrow, director of the Avian Sleep Group at the Max Planck Institute for Ornithology and leader of the study, Prof Bart Kempenaers noticed a peculiar behaviour.

"He discovered that these male pectoral sandpipers were being incredibly active throughout the 24-hour period," co-author Dr Niels Rattenborg told BBC News.

"We used a variety of methods to gain insight into what was actually going on up there. What were these sandpipers doing? We put transmitters on their back that could measure when they were moving. So we could record patterns throughout 24 hours, over a period of several weeks," Dr Rattenborg said.

By analysing these data, along with brain activity recordings, the team found that some male pectoral sandpipers were extremely active during the whole day, whereas others were engaging with fewer females, choosing instead to sleep.

You snooze, you lose

Dr Rattenborg and his colleagues then tested the paternity of the young that were laid on the site.

"We collected every egg on the study site, incubated them, hatched them and then got DNA from each of the chicks, so we could tell how many chicks a given male sired. Then we returned the chicks to the mothers out in the field," Dr Rattenborg said.

This paternal data proved that the individuals that were the most active - up to 95% of 24 hours - sired the most young, despite having hardly slept over a period of weeks.

Tags Male and female pectoral sandpipers were equipped with tags to monitor their activity

The behaviour may be linked to the mating strategy employed by the birds, as pectoral sandpipers are "polygynous", meaning males mate with many females during periods of intense competition, whereas other species of sandpipers concentrate their efforts on a single female.

"We also observed that the monogamous species of sandpipers nesting in exactly the same area had periods of inactivity during the dimmest part of the 24 hour period. So they seemed to be sleeping, where some of the male pectoral sandpipers are engaging in almost constant activity," said Dr Rattenborg.

The findings were a surprise to the team, especially as the sleep deprived males seemed to suffer no ill-effects, returning to the breeding site the following year.

"There's an extensive body of research looking at the effects that sleep loss has on performance in a variety of types of animals. Pretty much across the board these studies showed that even losing a relatively small amount of sleep, just a couple of hours a night, has adverse effects on our ability to perform waking functions," explained Dr Rattenborg.

Yet this appeared not to faze the "super-active" pectoral sandpipers with the individuals developing "adaptive" sleep loss being more successful, from an evolutionary point of view, even after migrating vast distances from the Southern hemisphere.

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