Many migratory birds could face extinction risks from loss of habitat on their long-distance flight paths, unless greater international protection efforts are initiated, researchers are warning.

Poorly-coordinated efforts at conservation on a global scale have left around 90 percent of the world's migratory birds inadequately protected, they say.

"More than half of migratory bird species travelling the world's main flyways have suffered serious population declines in the past 30 years," says Claire Runge of the University of Queensland in Australia.

"This is due mainly to unequal and ineffective protection across their migratory range and the places they stop to refuel along their routes," says Runge, lead author of a study led by the ARCE Center of Excellence for Environmental Decision and published in the journal Science.

The study found worrying gaps in the global conservation efforts directed at migratory birds, especially across India, China and parts of South America and Africa, the researchers report.

The problem arises because most migratory birds rely on a number of different geographic regions in their annual cycle of feeding, resting and breeding, Runge says.

Many species cross entire continents to seek out warmer habitats during winter months and for breeding, she points out, and long-distance migration puts a strain on the birds, which can lose a significant amount of their body weight during the journey.

"So even if we protect most of their breeding grounds, it's still not enough — threats somewhere else can affect the entire population," she explains. "The chain can be broken at any link."

Evidence of that is already being seen, the study authors note.

For the study, the scientists gathered data on the movement of migratory birds species throughout the year and compared this information with maps of protected areas in different habitats, including wetlands, savannas, forests, Arctic tundra and desert environments.

"We overlaid those two things on top of each other and asked how well protected each migratory species was across its whole annual cycle," says University of Queensland biologist Richard Fuller.

"We found that more than 90 percent of species have one or more parts of their life cycle poorly protected," he says.

Of 8,200 areas identified as internationally-important stopover points for migratory bird species, just 22 are completely protected, the researchers found.

While individual countries can protect habitats within their borders, to safeguard the globe's migratory birds will require international collaboration and coordination, they say.

"We need to work together far more effectively [a]round the world if we want our migratory birds to survive into the future," says Fuller.

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