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Mystery Unlocked: Bird Egg Shapes and Flight Ability are co-related, says Study

The analysis revealed that birds tend to lay eggs that are more asymmetric and more elliptical if they are better fliers

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Bird egg
Different shapes of bird eggs. Pixabay
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  • Team of researchers has found that the egg shape is related to flight ability
  • The team used photographs to analyze the shapes of nearly 50,000 eggs representing 1,400 species.
  • The egg membrane may also play a critical role in determining the shape

New York, June 24, 2017: In what could perhaps crack the long-term mystery behind the astonishing variety of bird egg shapes, an international team of researchers has found that the egg shape is related to flight ability, with good fliers tending to lay pointy or elliptical eggs.

Avian eggs have fascinated humans for millennia because they come in different shapes — elliptical in hummingbirds, spherical in owls, pointy ovoids in shorebirds and almost everything in between. But we still lack the answer to this simple question — why did different egg shapes evolve, and how?

The new study published in the journal Science suggests that egg shape is related to flight ability, and that the egg membrane may play a critical role in determining shape.

“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,” said the study’s lead author Mary Caswell Stoddard of Princeton University in New Jersey, US.

“In addition, we propose that the stretchy egg membrane, not the hard shell, is responsible for generating the diversity of egg shapes we see in nature,” Caswell said.

To unravel the mystery of egg shape, the researchers used a multi-step, multidisciplinary process, applying tools from computer science, comparative biology, mathematics and biophysics.

First, the team used photographs to analyse the shapes of nearly 50,000 eggs representing 1,400 species.

The eggs, from the online database of The Museum of Vertebrate Zoology at Berkeley, came from across the globe and were largely collected by naturalists in the late 19th and early 20th centuries.

Using computer code, the researchers quantified each egg’s asymmetry and ellipticity.

By combining the power of high-throughput digital image analysis with the wealth of data in the museum egg collection, the team was able to map the world of egg shapes.

The team then developed a biophysical model to explain how processes in the bird’s oviduct might generate different egg shapes.

The team also used an evolutionary framework to test hypotheses about egg shape.

Using a recently constructed phylogeny, or family tree, of birds, the researchers compared egg shapes across different bird lineages. In this analysis, they included details about nest type and location, clutch size, diet and flight ability.

Also Read: Why Birds have Beaks? Researchers discover a Dinosaur Species that shed its “Milk teeth” but did not Replace them 

The analysis revealed that birds tend to lay eggs that are more asymmetric and more elliptical if they are better fliers.

The researchers suggest that as birds’ bodies became adapted for powered flight, this resulted in morphological changes like reduced body size and a reduced abdominal cavity.

The discovery that morphological constraints associated with flight may contribute to egg shape challenges the conventional wisdom that egg shape is largely influenced by clutch size or nest location. (IANS)

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Rescue Efforts For Wild Puerto Rican Parrot In Motion

Scientists also are now collecting new data on the number of predators at El Yunque, including el guaraguao, a red-tailed hawk that hunts Puerto Rico parrots.

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Puerto Rican Parrot
A Puerto Rican parrot eats inside one of the flight cages in the Iguaca Aviary at El Yunque, Puerto Rico, where the U.S. Fish & Wildlife Service runs a parrot recovery program in collaboration with the Forest Service and the Department of Natural and Environmental Resources, VOA

Biologists are trying to save the last of the endangered Puerto Rican parrots after more than half the population of the bright green birds with turquoise-tipped wings disappeared when Hurricane Maria hit Puerto Rico and destroyed their habitat and food sources.

In the tropical forest of El Yunque, only two of the 56 wild birds that once lived there survived the Category 4 storm that pummeled the U.S. territory in September 2017. Meanwhile, only 4 of 31 wild birds in a forest in the western town of Maricao survived, along with 75 out of 134 wild parrots living in the Rio Abajo forest in the central mountains of Puerto Rico, scientists said.

And while several dozen new parrots have been born in captivity and in the wild since Maria, the species is still in danger, according to scientists.

 

Puerto Rican Parrots
Parrot eating a fruit. Flickr

 

“We have a lot of work to do,” said Gustavo Olivieri, parrot recovery program coordinator for Puerto Rico’s Department of Natural Resources.

Federal and local scientists will meet next month to debate how best to revive a species that numbered more than 1 million in the 1800s but dwindled to 13 birds during the 1970s after decades of forest clearing.

The U.S. and Puerto Rican governments launched a program in 1972 that eventually led to the creation of three breeding centers. Just weeks before Maria hit, scientists reported 56 wild birds at El Yunque, the highest since the program was launched.

But the population decline is now especially worrisome because the parrots that vanished from El Yunque were some of the last remaining wild ones, said Marisel Lopez, who oversees the parrot recovery program at El Yunque for the U.S. Fish & Wildlife Service.

Puerto Rican Parrot
These two Puerto Rican parrots were photographed at the aviary in El Yunque National Forrest after Hurricane Maria. Flickr

“It was devastating. After so many years of having worked on this project…,” she stopped talking and sighed.

The Puerto Rican Amazon is Puerto Rico’s only remaining native parrot and is one of roughly 30 species of Amazon parrots found in the Americas. The red-foreheaded birds grow to nearly a foot in length, are known for their secrecy and usually mate for life, reproducing once a year.

More than 460 birds remain captive at the breeding centers in El Yunque and Rio Abajo forests, but scientists have not released any of them since Hurricane Maria. A third breeding center in a forest in the western rural town of Maricao has not operated since the storm. Scientists are now trying to determine the best way to prepare the parrots for release since there are such few birds in the wild they can interact with, and whether Puerto Rico’s damaged forests can sustain them.

One proposal scientists

Puerto Rican Parrot
When in flight, some of the PR Parrots show their beautiful blue primary feathers. Flickr

Scientists are tentatively planning to release 20 birds next year in Rio Abajo.

Another proposal is to release more parrots in Maricao, which was not as heavily damaged by Maria.

“Our priority now is not reproduction. … it’s to start releasing them,” Lopez said, adding that breeding centers can hold only so many parrots.

But first, scientists need to make sure the forests can offer food and safe shelter.

Jessica Ilse, a forest biologist at el Yunque for the U.S. Forest Service, said scientists are collecting data about the amount of fruit falling from trees and the number of leaves shed. She said the canopy still has not grown back since Maria and warned that invasive species have taken root since more sunlight now shines through. Ilse said that many of the large trees where parrots used to nest are now gone and noted that it took 14 months for El Yunque’s canopy to close after Hurricane Hugo hit Puerto Rico in 1989 as a Category 3 storm.

Puerto Rican Parrot
Puerto Rican Parrot Recovery Program. Flickr

Scientists also are now collecting new data on the number of predators at El Yunque, including el guaraguao, a red-tailed hawk that hunts Puerto Rico parrots. Without a canopy and proper camouflage, wild parrots have become an easy target.

Ilse said local and federal scientists plan to help the forest recover through planting. By the end of November, they expect to have a map detailing the most damaged areas in El Yunque and a list of tree species they can plant that are more resistant to hurricanes.

Also Read: India To Release 8 Endangered White-Backed Vultures In The Wild

“People keep asking us, ‘How long is it going to take?'” Ilse said.

But scientists don’t know, she added.

“The damage is more extensive than [hurricanes] Hugo and Georges. … It’s been a complete change to the ecosystem.” (VOA)