According to a new study published in the journal Science, more than 90 percent of migratory bird species are without adequate protections.

The research reveals the difficulty in protecting migratory species, whose journeys can span hundreds of thousands of miles over a lifetime.

"A typical migratory bird relies on many different geographic locations throughout its annual cycle for food, rest and breeding," study author Claire Runge, a researcher with the ARC Centre of Excellence for Environmental Decisions (CEED) and the University of Queensland, said in a press release.

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

Runge and her colleagues analyzed the findings of previous research efforts concerning some 1,451 migratory bird species, of which 1,324 face inadequate habitat protection for at least a portion of their journey.

The study makes starkly clear the importance of habitat protections for migratory birds. It's no coincidence that of the migratory species included on the International Union for Conservation of Nature Red List by BirdLife International, fewer than 3 percent are adequately protected.

"For example, the red-spectacled amazon -- a migratory parrot of Brazil -- is threatened by habitat loss," said study co-author Stuart Butchart, the head scientist at BirdLife International. "And yet less than four per cent of its range is protected, and almost none of its seasonal breeding areas in southern Brazil are covered."

One of the problems is a lack of coordination among nations.

"For instance, Germany has protected areas for over 98 percent of the migratory species that pass its borders, but fewer than 13 percent of its species are adequately protected across their global range," said co-author Richard Fuller of CEED.

Fuller said there isn't necessarily a divide between wealthier and less developed nations.

"Many Central American countries, for example, meet the targets for more than 75 percent of their migratory species, but these same species have less protected area coverage in Canada and USA."

The key is adequate protection everywhere. To facilitate coordination, the study's authors highlighted several thousand areas where protections are lacking for many migratory species.

The largest protection gaps in habitat crucial to lots of bird species were located in China, India and parts of Africa and South America.