Being the first-born may not be so good after all

Washington, Mar 12 : Contrary to a common perception that baby birds that are laid before their siblings have a better chance of survival, a new study at University of North Carolina at Chapel Hill has shown that the first-laid eggs are in fact least likely to hatch at all.

Keith Sockman, an assistant biology professor in UNC's College of Arts and Sciences along with his team studied the Lincoln's sparrows in a remote stretch of Colorado's San Juan Mountains for three breeding seasons.

"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.

During the study the team observed that female Lincoln's sparrows lay one egg per day, usually producing three to five eggs in total.

Mothers do not settle down and start incubating the eggs right away, since they still have other concerns during the laying cycle, such as scavenging for food.

Sockman deems that this leads to lower likelihood of the first-laid eggs to hatch at all, though it 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," he added.

It is a known fact that youngest hatchlings often die, as they're too small to compete against their feistier siblings for the limited resources provided by their parents.

"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.

ANI