Why do eggs have a blunt and sharp end?

2024 Author: Seth Attwood | [email protected]. Last modified: 2023-12-16 15:55

Many birds' eggs are sharpened at one end to prevent them from rolling out of nests located on uneven surfaces. This is the conclusion reached by biologists who observed the life of Arctic birds and published their findings in the Journal of Experimental Biology.

“We found that the difference in size between the blunt end and the sharp end of the egg had the strongest effect on how quickly it rolled down an incline. This explains why guillemots and many other birds that nest on rocks and steep banks lay very asymmetrical eggs,”says Mark Hauber of the University of Illinois at Chicago, USA.

The eggs of many birds, unlike crocodiles, dinosaurs and other reptiles, are often conical and very elongated. How this unusual feature of eggs arose and what role it played in the evolution of birds has long worried not only the midgets from "Gulliver", but also evolutionary scientists.

For example, they recently found out that the general shape of the egg and the degree of its elongation does not depend on the size of the bird, but on how well it can fly and how often it does it. Discoveries like these have prompted Hauber and his colleagues to ponder how differences in the size of the blunt and sharp ends of eggs could have arisen during the evolution of birds.

Comparing the clutches of different birds, scientists drew attention to the unusually pointed eggs of thick-billed guillemots, similar in shape to a pear. Guillemots live in bird colonies beyond the Arctic Circle, setting up giant colonies on sheer cliffs located on the very shores of the Arctic Ocean.

During the breeding season, they form pairs and lay their eggs directly on the rocks, making nests at the very edge of the cliffs. This fact prompted scientists to think that the pear-like shape of murre eggs can help them keep themselves in place and not slide into the abyss.

They checked whether this is actually so by 3D-printing several dozen replica eggs of guillemots and other birds, which have a more "symmetrical" shape. As it turned out, pointed eggs rolled much worse off sloped surfaces than their rounder rivals.

Interestingly, long and "thin" eggs rolled much better than other dummies, but such characteristics influenced the likelihood of their "escape" from the nest much less than the difference in size between blunt and sharp ends.

Likewise, according to Hauber and his colleagues, evolution could have influenced other properties of eggs, including yolk and white size, total egg weight, and other properties that subtly affect whether a bird's offspring survive or die.

Studying them will help us uncover the secrets of how feathered dinosaurs turned into birds and in what conditions they lived.