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Researchers have longtime been interested in deciphering the migratory habits of songbirds, but it wasn’t until recently that they managed to follow them on full migratory routes, with the help of miniaturized geolocators placed on 14 wood thrushes and 20 purple martins. The findings are reported in the February 13 issue of the journal Science.
The conventional satellite tracking was not a viable method of watching the songbirds all throughout their migratory journey, so researchers had to think of an alternative. Placing a tracking device on these birds proved challenging considering their size (they weigh less than 50 grams), so researchers created miniaturized geolocators that they’ve successfully attached to the backs of the birds.
The tracking equipment placed on birds breeding in Pennsylvania during 2007 revealed not only the complete route of these birds, but also the fact that their flight capabilities have been so far underestimated. The migratory songbirds traveled to South America, and back to North America at speeds three or four times greater than previously thought.
The average flight performance had initially been estimated at 150 km (93 miles) per day; however, the new geolocator data indicated that migratory songbirds can fly over 577 km (358 miles) per day. The scientists also found that for one of the birds, it took 43 days to reach Brazil during the fall migration, but it took only 13 days to get back from the Amazon to Pennsylvania.
Here is what Bridget Stutchbury, professor of biology at York University’s Faculty of Science & Engineering in Toronto and lead author of the study, had to say about the amazing performance:
Never before has anyone been able to track songbirds for their entire migratory trip […] We were flabbergasted by the birds’ spring return times. To have a bird leave Brazil on April 12 and be home by the end of the month was just astounding. We always assumed they left sometime in March.
The tracking devices also answered some questions about the songbird populations, which have been declining for the past three or four decades by approximately 30 percent. The researchers found that wood thrushes from a single breeding population wintered in a small region in eastern Honduras or Nicaragua, instead of scattering over the tropical wintering grounds. This, researchers said, is a very important discovery as it puts in perspective the devastating effects heavy deforestation in this small region would have over the wood thrushes.
Tracking birds to their wintering areas is also essential for predicting the impact of tropical habitat loss and climate change, said Stutchbury. Until now, our hands have been tied in many ways, because we didn’t know where the birds were going. They would just disappear and then come back ion spring. It’s wonderful now to have a window into the journey.
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