Early bird doesn't always get worm, researcher finds

Mar 12, 2008

Competing against older brothers and sisters can be tough work, as any youngest child will tell you. But new research from a biologist at the University of North Carolina at Chapel Hill shows that when it comes to some birds, you should reserve any underdog sympathies for the first born – or rather, first laid – siblings as well.

The finding, published in the March 12 issue of PLoS ONE, runs somewhat counter to common wisdom, which holds that baby birds that are laid before their brood mates have a better chance of surviving long enough to leave the nest.

But after studying a population of Lincoln’s sparrows in a remote stretch of Colorado’s San Juan Mountains, Keith Sockman, an assistant biology professor in UNC’s College of Arts and Sciences, has discovered that first-laid eggs are, in fact, the least likely to hatch at all.

“I believe this is the first study to follow siblings from laying through fledging and demonstrate that the effect of laying order on hatching is very different from its effect post-hatching,” said Sockman.

It is a well-documented fact that being born just a day or so later often sets the stage for a situation whereby youngest hatchlings die. That’s because they’re too small to compete against their feistier brood-mates for the limited resources provided by their parents. Such competitive disparities caused by hatching or birth order can be found in other animals – from beetles to marsupials to humans – which sometimes produce their young in series, then rear the resulting offspring simultaneously.

But Sockman says up until now, such observations have usually failed to take account of what happens to eggs before they hatch.

Female Lincoln’s sparrows lay one egg per day, usually producing three to five eggs in total. While carefully observing and tracking the tiny birds for three breeding seasons, Sockman and his team of researchers noticed that typically, mothers do not settle down and start incubating the eggs right away, since they still have other concerns during the laying cycle, such as foraging for food.

Sockman believes this contributes to the lower probability that first-laid eggs will hatch at all – but also helps to ensure that overall, a greater number of reasonably healthy, strong and feisty chicks hatch and go on to develop into young birds.

“At these elevations, conditions can be fairly harsh even during the summer when Lincoln's sparrows breed,” said Sockman. “It’s often freezing at night, which is hard on an un-incubated egg, while daytime temperatures are warm enough to foster the growth of harmful microbes. As a result, since the mother sparrow isn’t keeping them at the most optimal incubating temperature from day one, first-laid eggs can be exposed to environmental conditions that lower the chance those embryos will ever see the world outside their shell.”

“If the female did start incubating all her eggs as soon as she laid them, it would increase the probability they’d all hatch. But it would also give a huge head start to those first-laid eggs and the chicks that emerge from them, putting their younger siblings at even more of a competitive disadvantage once they begin battling for food and their mother’s attention,” said Sockman. “It may also reduce the number of eggs she is capable of laying.”

The mother’s careful balancing of this trade-off enables her to end up with three or four relatively equally robust offspring, instead of one or two strong hatchlings and several “runts of the litter,” said Sockman.

Sockman now intends to examine what, if any repercussions laying order has once young birds reach adulthood. “The severely competitive environment in the nest may have consequences on the individual's ability to compete for resources and mates the following year when it is reproductively mature,” said Sockman.

Source: University of North Carolina at Chapel Hill

Explore further: Parasitic worm genomes: largest-ever dataset released

add to favorites email to friend print save as pdf

Related Stories

Bridgmanite: World's most abundant mineral finally named

12 minutes ago

A team of geologists in the U.S. has finally found an analyzable sample of the most abundant mineral in the world allowing them to give it a name: bridgmanite. In their paper published in the journal Science, the te ...

Pop music heritage contributes to the formation of identity

32 minutes ago

The musical rebels of the past are today's museum pieces. Pop music is increasingly penetrating heritage institutions such as museums and archives. That is apparent from the PhD research of Arno van der Hoeven. On Thursday ...

Male sex organ distinguishes 30 millipede species

33 minutes ago

The unique shapes of male sex organs have helped describe thirty new millipede species from the Great Western Woodlands in the Goldfields, the largest area of relatively undisturbed Mediterranean climate ...

Orion on track at T MINUS 1 Week to first blastoff

49 minutes ago

At T MINUS 1 Week on this Thanksgiving Holiday, all launch processing events remain on track for the first blast off of NASA's new Orion crew vehicle on Dec. 4, 2014 which marks the first step on the long ...

Helping older employees stay in their jobs

52 minutes ago

Factors that can hinder older employees from continuing to work include workload, a poor memory and the pensionable age-effect. The Job-Exposure Matrix is a newly developed instrument that provides an easy way to chart the ...

Recommended for you

Parasitic worm genomes: largest-ever dataset released

6 hours ago

The largest collection of helminth genomic data ever assembled has been published in the new, open-access WormBase-ParaSite. Developed jointly by EMBL-EBI and the Wellcome Trust Sanger Institute, this new ...

Male sex organ distinguishes 30 millipede species

7 hours ago

The unique shapes of male sex organs have helped describe thirty new millipede species from the Great Western Woodlands in the Goldfields, the largest area of relatively undisturbed Mediterranean climate ...

How can we avoid kelp beds turning into barren grounds?

11 hours ago

Urchins are marine invertebrates that mould the biological richness of marine grounds. However, an excessive proliferation of urchins may also have severe ecological consequences on marine grounds as they ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.