Early birth is not always beneficial

Competition with older siblings has always been a difficult job, any child can tell you this. But the new study by a biologist at the University of North Carolina at Chapel Hill shows that for some birds, the first born - or more precisely, the first hatched - are the ones loss needs sympathy.

This finding seems to be contrary to common sense, that in the same litter, pre-born young birds have more chances to survive to leave the nest.

But after studying some Lincoln sparrow in a remote stretch of the San Juan Mountains in Colorado, Keith Sockman, assistant professor of biology at the UNC College of Arts and Sciences, discovered. that the eggs are laid first, are actually the hardest to hatch.

'I believe this is the first study to track young birds from spawning until birth and prove the consequences of the order of laying on the process before and after the eggs are very different.' Sockman said.

Newly born Lincoln finches (Photo: Keith Sockman)

In fact, the fact that being born only about a day later often creates a situation where the last child dies. That is because they are too small to compete with the limited food that parents provide, with more aggressive peers. Inadequate competition created by this birth order can be found in many animals. another - from beetles, marsupials to humans - sometimes giving birth continuously, then raising them all at once.

But Sockman said that such observations often cannot explain what happened to the eggs before hatching.

Normally Lincoln sparrows lay one egg a day, about three to five eggs in total. While carefully observing and tracking tiny birds over three breeding seasons, Sockman and colleagues in the research team found that the mother bird did not park and started brooding right away, because they still had concerns. other minds in the egg-laying cycle, such as finding food.

Sockman believes that this contributes to reducing the chance of hatching the first laid eggs - but helps ensure that a larger number of healthy and aggressive offspring expand and continue to grow into birds. young'At this height, environmental conditions can be quite harsh even in the summer when Lincoln sparrows give birth,' Sockman said. 'The night is usually cold, this is very unfavorable for eggs that have not been hatched. , while during the day the temperature is high enough for harmful germs to grow. Since the mother bird is not kept at the appropriate incubation temperature right from the first day, pre-laid eggs may suffer from the harsh environment and thus reduce the chance of hatching into young birds to see the world. outside.'

' If the female immediately incubates all eggs when she has just given birth, it is likely that all of the eggs will hatch into a baby. But it also provides a very good start for pre-laid eggs, and young hatchlings will have a hard time entering the competition for food and care of the mother bird . ' Sockman explains: 'This also reduces the number of eggs that a mother bird can lay.'

"The adjusted caution of the mother bird allows it to have three to four equally healthy offspring, instead of one or two healthy young birds rising and some stunting," Sockman added.

Sockman now intends to study whether the order of birth affects the lives of birds when it matures? 'The fiercely competitive environment in the team can affect each bird's ability to compete for food and partners in the next few years when it is mature and fertile,' Sockman concluded.

The study, entitled ' Order of reproduction, mediates the balance of pre-hatching survival and postnatal survival ' published on PLoS One on March 12.