Image copyright SPL Image caption Turkey vultures are a very common species in North America

Some species of vultures have developed the ability to tap into turbulent air as a way of gaining altitude according to a new study.

Researchers found that these species compensate for their poor flapping skills by seeking out turbulence at low altitudes.

The researchers say this explains their awkward, wobbling flying style near tree-tops.

The study is published in the journal The Auk: Ornithological Advances.

Sometimes called buzzards, Turkey vultures are the most widespread of these species in North America

They are unique among these birds as they use their sense of smell to find carrion.

For this study researchers in this study observed both Turkey and Black vultures in south eastern Virginia in the US.

According to the study's lead author Julie Mallon, then at the University of West Virginia, these particular vultures have evolved a different style of flying, skirting low along the edge of forests.

"It's an energetic thing," she told BBC News.

Image copyright Michael DiGiorgio Image caption A graphical representation of how vultures use tree top turbulence

"They don't have the muscular power other raptors like eagles have to give chase, vultures don't pursue their prey and they've lost a lot of those adaptations that allowed them to do that and one of those is sustained flapping flight."

In the place of sustained flapping, they've developed the ability to tap into the small scale turbulence that occurs when horizontal air currents hit the edge of a forest or a similar barrier.

The disturbance usually produces a small uplift that the vultures utilise to stay aloft. Researchers have termed this manoeuvre "contorted soaring".

"They are very close to the trees, often only a metre above them, they look like they are going to crash but they stay aloft, its really amazing to see," said Julie Mallon.

"They are generally following a straight line, but they will move suddenly to one side or bump up and down like a roller coaster."

"It's not a very smooth flight, but at the same time it's very graceful, the way they can keep catching air."

Image copyright SP Carey Image caption Turkey vultures' strong stomach acid helps them survive on a diet of rotting meat

The scientists believe that by staying low, Turkey vultures increase their chances of sniffing carrion while avoiding the notice of higher flying birds that use visual cues to spot food.

The researchers made the discovery by the rather old fashioned method of observation - Scientists used binoculars to watch the vultures over long periods of time and record their altitudes and different types of flight.

"This paper is a real step forward in the study of vultures and other birds that use soaring flight for efficient movement across large areas," said USDA scientist Travis DeVault, an expert on the ecology of scavengers.

"Kudos to them for recognizing and describing this behaviour, which is probably used by many species worldwide."

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