Scientists have previously documented how bird migrations around the world are happening earlier every year. Recently, researchers from the University of East Anglia’s Schools of Biological Sciences in the U.K. fingered climate change as the culprit for early godwit migrations in Europe.

“We have known that birds are migrating earlier and earlier each year – particularly those that migrate over shorter distances,”  Jenny Gill, a biologist from the University of East Anglia and one of the authors of a bird migration study, said in a statement, according to Red Orbit. “But the reason why has puzzled bird experts for years. It’s a particularly important question because the species that are not migrating earlier are declining in numbers.”

The team observed Icelandic black-tailed godwits, a group of large, long-billed, thin-legged migratory birds, for 20 years. Over that period, they found that the birds were flying the coop two weeks earlier than in previous years. According to their report, published in the Proceedings of the Royal Society B, researchers were helped by more than 2,000 birdwatchers, who reported sightings of the godwits over Iceland, Spain and Portugal.

“Climate change is likely to be driving this change, because godwits nest earlier in warmer years, and birds that hatch earlier will have more time to gain the body condition needed for migration and to find good places to spend the winter, which can help them to return early to Iceland when they come back to breed,” Gill explained.

According to Science World Report, researchers found that global warming seems to be causing birds to nest and hatch earlier in the year. With 2013 recently being dubbed the seventh warmest year on record – this year has seen record heat waves in Australia and floods all over from Sudan to Europe, and Japan had its warmest summer on record – this could explain why birds are hatching sooner. This highlights the long-term trend of higher global temperatures.

"The obvious answer would be that individual birds are simply migrating earlier each year,” Gill said in a statement. “But our tracking of individual birds shows that this is not the case. In fact, individual birds do almost exactly the same thing every year - arriving punctually at the same time year-on-year," Gill said.

This isn’t the first scientific report to highlight the early migration trend among migratory birds. A study from February 2012 from the University of North Carolina at Chapel Hill found that North America birds were speeding up the tempo when it came to heading south for the winter.

"Timing of bird migration is something critical for the overall health of bird species," Allen Hurlbert, a professor of biology at the University of North Carolina, said in a statement. "They have to time it right so they can balance arriving on breeding grounds after there's no longer a risk of severe winter conditions. If they get it wrong, they may die or may not produce as many young. A change in migration could begin to contribute to population decline, putting many species at risk for extinction."