The fact that eggs are shaped different has baffled scientists for centuries. But a team of scientists from Princeton University may have found a reason as to which this is so.
Eggs Are Shaped Different Depending on Bird’s Flight Capacity
The reason that eggs are shaped different is tied to the time that a bird spends flying. The fact that scientists have long emitted hypotheses about the reasons of different shapes of eggs is no new news. Aristotle, for example, thought that
“Long and pointed eggs are female; those that are round, or more rounded at the narrow end, are male”.
This was written by Aristotle in The History of Animals, published in the fourth century B.C. But, recently, scientists may have found another reason to account for the fact that eggs are shaped differently. One reason would be that it is an evolutionary advantage for birds that nest in tall cliffs. It thus prevents tumbles over the cliff edge, making the eggs roll in a tight circle.
Mary Stoddard, an evolutionary biologist at Princeton University, took into consideration a vast amount of egg shape data to understand exactly why eggs are shaped differently.
She and her team started compiling a database of egg images from the Museum of Vertebrate Zoology at UC Berkeley. Then, the team developed a software that can scan the images and extract information in detail pertaining to the eggs’ size and shape. The software analyzed a total of 13,049 images that contain 49,175 individual bird eggs, which appertain to 1,400 different species, including members of every bird family.
Then, the team mapped the full range of egg shapes. Depending on the geographical position in which the eggs were nested, the team found two factors standing out.
The first one was the egg’s overall size. The larger the egg, the more it must be compressed to fit through the mother’s narrow oviduct. Then, and this was the surprising reason for the team as to why eggs are shaped differently, deals with the bird’s hand-wing index. The hand-wing index is a measure that shows how pointed and elongated are the bird’s wings. And biologists use this measure as a proxy for flight strength.
It would appear that eggs are shaped differently because birds evolve to become stronger fliers. This results in a shift of their body, which may have become more streamlined. This impacts the shape of their eggs, the scientists hypothesize.
Image Source: Flickr