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Difference in Egg Shapes in Birds No Longer a Mystery

Despite the fact that the prime purpose of all eggs is to protect and nourish the developing chick inside, they come in different shapes and sizes. For instance, Owls have spherically shaped eggs, hummingbirds’ eggs are elliptical whereas sandpipers’ are pointy. So, what is the reason behind the variation in the shapes of birds’ eggs? researchers think they have cracked the puzzle.

Scientists from various fields have teamed up to perform one of the most comprehensive researches on egg shells. According to the study, which was published in the journal Science, it has to do with the bird’s flight capabilities and the structural adaptations resulting from a long period of evolution.

In the previous researches, scientists had formulated different hypotheses to explain the phenomenon, such as:

•    Birds with a limited supply of calcium in their diet lay rounded eggs to cut on the amount of shell material.

•    Birds that build their nests on cliffs have more pointed eggs to protect their eggs because pointed eggs will spin in a circle rather than fall off when bumped.

•    The different shapes of eggs are necessary so they can better fit in a nest, enabling equal incubation of all the eggs.

Since the hypotheses had neither been tested nor verified, a team of researchers from Harvard, Princeton, and other learning institutions took up the task of unscrambling the mystery. According to the study, the shape has majorly been affected by the ability of the bird to soar high in the sky and fly fast over long distances.

In their research, scientists analyzed close to 50,000 photographs of eggs from 1,400 bird species all over the world. The eggs were collected in the late 19th and early 20th centuries by naturalists and their pictures are stored in an online database belonging to the Museum of Vertebrate Zoology in Berkeley, California.

The research was enhanced by a computer program written by the team, which they named ‘Eggxtractor’. The program was designed to take width and length measurements from all the photographs. Those measurements were then used to determine the extent to which the eggs were elongated, pointy and spherical. The results showed that some eggs fell under several shape categories while others took only one. However, no eggs were both short and pointy.

Another key input in the study was the knowledge that the shape of eggs from the same bird is determined by the membrane and not the egg shell. Evolutionary biologist Mary Stoddard from Princeton University worked alongside L. Mahadevan, a physicist at Havard University and his student Ee Hou Yong to formulate a mathematical model based on how much pressure the membrane received (from the chick growing inside), and it’s properties.

 Stoddard and her team then used the model to extrapolate egg shapes by varying the two parameters. They used the data to compare egg shapes across different bird species. In the comparisons, they took into consideration various characteristics — like how big the birds were, where they made their nests, their diet and flight prowess. According to Stoddard, the results showed that none of the above characteristics create a consistent trend, apart from how good the birds were at flying. Birds that are excellent at flying had more asymmetrical eggs that were pointier and more elongated.

The explanation: As bodies of birds evolved to become better adapted for flight, they acquired a more sleek and streamlined shape. Their internal organs also became more compressed to take shape. For example, their oviducts became stretchier. Within the oviduct, a stretchy membrane that gives eggs their shape is formed around the white and yolk before the egg shells are cast. Therefore the membrane took the slender shape of the tube. The structure also enabled eggs to pack as many nutrients as possible

For instance, fast and powerful fliers like common murres have evolved to have asymmetric eggs. So have sandpipers, which are known to migrate over long distances. Wondering albatross have elliptical eggs, and they are one of the farthest flying birds. On the other hand, Eastern screech owls hardly explore life beyond their small territory. They fly with little low-powered glides. As a result, their eggs take a more spherical shape.

However, other biologists have argued that the research is far from over. In a perspective published alongside the Science paper, Claire Spottiswoode (who did not participate in the study) said, “This discovery will be far from the final word”.  Among the questions raised was:  Why do birds that are not as excellent at flying lay more rounded eggs? How does it affect the ease with which the chicks hatch? Stoddard herself added that she had more questions now than she did at the start. “I think that is the surprising wonder that came with the study,” she said.

 

Comments: Title with important words should be in all caps...titleshould be short, terse and direct to the point. Otherwise perfect writing. Thank you

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