பறவை முட்டையின் வடிவமும் பறக்கும் திறனும்

பறவைகளின் முட்டைகள் பலவித வடிவங்களில் இருப்பதற்கு  பறவையியல் வல்லுனர்கள் பல காரணங்களை சொல்கின்றனர். உயரமான கூடுகளிலிருந்து உருண்டு விழாமல் இருக்க நீள் வட்ட முட்டைகளும், கீழே விழுந்தால் உடையாமல் காக்க, கோள வடிவ முட்டைகளும் உருவாகியிருக்கலாம் என்பது பலரது கருத்து.

ஆனால், அண்மையில், 14,000 பறவையினங்களின் 50 ஆயிரம் முட்டைகளின் வடிவங்களை ஆராய்ந்த ஹார்வர்டு மற்றும் பிரின்ஸ்டன் பல்கலைக்கழக (Harvard University and Princeton University ) ஆராய்ச்சியாளர்கள், பறவைகளின் பறத்தல் திறனைப் பொறுத்து அவை இடும் முட்டைகளின் வடிவங்கள் மாறுபடக்கூடும் என்று விளக்கமளித்துள்ளனர்.

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பறக்கும் திறன் வலுவாக உள்ள பறவைகளின் உடல் அமைப்பு பறப்பதற்கு ஏற்ற வகையில் இருப்பதால், அவற்றின் இனப் பெருக்க உறுப்பு சிறியதாக அமைந்திருக்கும். எனவே, அவை இடும் முட்டைகள் நீள்வட்ட வடிவில் இருக்கின்றன என்று ஆராய்ச்சியாளர்கள் விளக்கம் தந்துள்ளனர்.

4

Why Do Bird Eggs Have Different
Shapes? Look to the Wings

Owls’ are spherical, hummingbirds’ are elliptical and sandpipers’ are pointy.

All bird eggs have the same function — to protect and nourish a growing chick. But they come in a brilliant array of shapes. This variety has puzzled biologists for centuries. Now, in the most comprehensive study of egg shapes to date, a team of scientists seems to have found an answer.

The researchers cataloged the natural variation of egg shapes across 1,400 bird species, created a mathematical model to explain that variation, and then looked for connections between egg shape and many key traits of birds. On a global scale, the authors found, one of the best predictors of egg shape is flight ability, with strong fliers tending to lay long or pointy eggs.

The authors conducted a multistep investigation that brought together biology, computer science, mathematics and physics. They first wrote a computer program, named Eggxtractor. With Eggxtractor, the researchers plotted nearly 50,000 eggs, representing all major bird orders, from a database of digital images by the Museum of Vertebrate Zoology in Berkeley, Calif.

Next, the researchers attempted to answer how eggs might acquire varying shapes. Rather than looking at the shell, as one might expect, they focused on the egg’s membrane (the film you see when peeling a hard-boiled egg), which is essential to the egg’s shape.

The scientists identified two parameters that could influence egg form: variations in the membrane’s composition and differences in pressure applied to the membrane before the egg hatches.

By adjusting these two parameters, “we were able to completely recover the entire range of observed avian egg shapes” — a good test of the model, said L. Mahadevan, a professor of applied math, biology and physics at Harvard University and an author of the study.

Finally, the researchers looked into why egg shapes might be so spectacularly diverse. One popular hypothesis centered on nest location: Cliff-nesting birds, it was thought, lay pointy eggs so that if the eggs are bumped, they spin in a circle rather than rolling off the cliff. Another suggested that birds lay eggs in shapes that pack together best in different-size clutches.

But when the authors related egg shape to these and other variables, they were surprised to find that none of them fit on a global scale (though they may still play important roles on smaller scales). Instead, egg shape was strongly correlated with a measure of wing shape, called the hand-wing index, which reflects flight ability.

Wandering albatrosses are one of the most far-ranging fliers — some have been known to circumnavigate the Antarctic Ocean three times in a year — and have elliptical eggs. Eastern screech owls rarely move beyond their small territory, where they tend to fly in short, low-powered glides, and have almost spherical eggs.

Source : Dinamalar and New York Times

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