Birds of a Feather
Do younger siblings get all the breaks? A new study reveals how birth order in birds influences survival
First is the worst, second is the best? Many first-born siblings have long believed their parents favor the younger child over the oldest and in the world of birds, that may in fact be the case.
A new study out of the University of North Carolina-Chapel Hill shows that first-laid eggs are actually the least likely to hatch.
While the youngest hatchlings, too small to counter their brothers and sisters in the scrum for the limited food provided by their parents, are the most likely to die after birth, it is the first-laid egg that has the worst chance of even hatching at all.
“I believe this is the first study to follow siblings from laying through fledgling and demonstrate that the effect of laying order on hatching is very different from its effect post-hatching,” said Keith Sockman, assistant biology professor at UNC-Chapel Hill.
Sockman believes that the reason for the trend is because mother birds typically do not start incubating the eggs until after they have gathered food. At the same time, he supposes that this is why so many chicks live to become young birds.
“If the female did start incubating all her eggs as soon as she laid them, it would increase the probability they’d all hatch,” Sockman said. “But it would also give a huge head start to those first-laid eggs and the chicks that emerge from them, putting their youngest siblings at even more of a competitive disadvantage once they begin battling for food and their mother’s attention.”
No conclusions or parallels have been drawn between the bird study and humans, which means the verdict is still out on why parents are so unfair in the first place.
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