Island birds are losing their ability to fly. This has been revealed by a recent study conducted in New Zealand, known as a home for the weka, takahe, flightless ducks and kakapo. (Photo : Mike Hewitt/Getty Images)

Island birds are losing their ability to fly. This has been revealed by a recent study conducted in New Zealand, known as a home for the weka, takahe, flightless ducks and kakapo.

A total of 868 species was studied by Natalie Wright of the University of Montana. She gathered the data from among these species and found out that island birds have much smaller flight muscles than those who live in the mainland. This means that island birds are beginning to lose their ability to fly, a condition known as flightlessness, according to National Geographic.

"Pretty much all island birds are experiencing these pressures to reduce flight, even if some can't go to the extreme," said Natalie Wright.

The difference in their flight muscles size is because of the amount of predators present in the island. Island birds have the leverage of staying on the ground more often as there is less risk of predator attack. This is exactly the opposite on mainland birds as they will have to exercise flying more to keep and protect themselves from the danger of land animal attacks, according to Proceedings of the National Academy of Sciences of the United States of America.

The study, which began 20 years ago to find out why birds are loosing ability to fly, caused Wright to travel to five different natural history museums and examine bird skeletons. Measuring the size of each bird's leg and breastbone, she was able to identify the possible size of muscles these parts of the birds' bodies had.

Tree Swallow Nest Box Projects said that breast sternums, also known as the breastbones, carry the most significant flying part of a bird's body. The breast and shoulder muscles, which are considered as the flying muscles of a bird, make up 30 to 50 percent of its body.

Breastbones of birds from islands were found to be smaller and their limbs longer. This means that they had bigger muscles on their legs and smaller ones on their breasts; evidence that they used their leg muscles more often than the muscles they use for flying.

To know more about birds and their diminishing fight ability, watch this video.