A recent study in the US Journal Science says that the variety observed in the shapes of an egg depends on how well the bird flies.
Until now, scientists had theories that suggested why the shape of the eggs is different and what could be the factors that are responsible for different shapes of eggs. One finding is that the flexible inner membrane of the egg, not the hard outer shell, is what generates the diversity of eggs out there in the nature. The other is that the variety of egg shape was dependent on the place where the bird places their nest determined the shape of eggs. For example, if a bird nests near a cliff, they often lay eggs that are cone shaped so that if they roll – they would do so in a tight circle and do not fall off the precipice.
To settle this debate, researchers looked at the shape of around 49,175 eggs from around 1,400 species of birds including the extinct species. This was provided from the database stored at the Museum of Vertebrate Zoology at the University of California, Berkeley. The eggs were then classified on basis of their shapes – asymmetrical or elliptical and also by bio-metric and environmental parameters. After creating a mathematical model they studied the associations between the shape of the egg and the physiological traits of the birds. This research determined that the best parameter to predict the shape of an egg is the bird’s skill at flying.
A biologist at Princeton University and one of the lead authors of this study, Mary Caswell said, “In contrast to classic hypotheses, we discovered that flight may influence egg shape. Birds that are good fliers tend to lay asymmetric or elliptical eggs.” Co-author Joseph Tobias of Imperial College London said, “The variation in size and shape is related to differences in ecology, particularly the extent to which each species is designed for strong and streamlined flight.”