Published: Saturday, August 22, 2015
A new mystery is unfolding in the migratory behavior of birds.
Billions of songbirds travel long distances during their annual migrations — up to 18,600 miles in a single year. Researchers have long believed that, in order to conserve energy, these birds might pick an altitude with favorable winds and stick with it rather than climbing and descending repeatedly.
A new study by University of Michigan-Dearborn Assistant Professor of Biology Melissa Bowlin shows that’s not necessarily the case. Bowlin and her colleagues recently completed the first full-altitude flight data for migrating songbirds and found that Swainson’s thrushes (Catharus ustulatus) made repeated altitude adjustments of more than 100 meters over the course of their nighttime migratory flights.
“We expected the birds to behave like commercial aircraft, ascending to a particular altitude, leveling off and cruising near that altitude, and then coming down just before they landed,” Bowlin said. “I was shocked when I made the first graph for the first bird, and thought it was an anomaly—maybe the transmitters weren’t working correctly. The more data we obtained, however, the more often we saw the up-and-down pattern to the birds’ flight.”
The team of researchers equipped the birds studied with radio transmitters to measure both air temperature and air pressure. From these two sets of data, the team could determine the altitude of the birds and discovered that thrushes change altitude midflight both dramatically and often: The graphs in Bowlin’s paper, which represent the birds’ altitude, show multiple peaks and valleys over periods of several hours.
No comments:
Post a Comment