‘Birds flock together while migrating at night’

July 8th, 2008 - 3:48 pm ICT by IANS  

Washington, July 8 (IANS) In a first, a new study has corroborated statistically what many ornithologists have long suspected — that most birds fly in flocks even at night. Researchers have spent decades trying to track how birds migrate at night, a problem compounded by their tiny size flying and the great height at which they fly.

Previous studies “sometimes very strongly suggested that the birds were flying tens of meters apart and yet somehow keeping together. But the evidence for this was ‘indirect and suggestive’”, said Robert Larkin, wildlife ecologist with the Illinois Natural History Survey.

Even if birds were presumed to be flying in groups, no one knew whether they were simply being swept along together passively or whether they were actively, intentionally, travelling together, Larkin said.

Now, researchers have used stationary light beams, radar-mounted tracking spot lamps and long-range radar to try to figure out what is going on in the night sky.

Decades of such observations suggest that birds do travel together, but not in compact flocks, as in daytime, said Larkin.

In the new study, the researchers took a fresh look at bird-flight data Larkin had collected in the 1970s and 1980s using low-power-density tracking radar.

The radar directed microwaves in a narrow cone - a “pencil-beam” — that could be pointed at virtually any target within range.

“If there is a bird target here, you can see it on the radar display as an echo,” Larkin said. “You throw a switch and it locks onto the target, it tracks the target, and wherever the bird flies, the radar points at it.”

In collecting the data, Larkin had used the radar in a new way. Once the radar operator had identified a flying object that might be a bird and began tracking its flight, he or she looked for other objects entering the radar’s beam.

If another potential target appeared, the radar could follow it for a few seconds before switching back to the first. By repeatedly switching back and forth between two targets, the operator could potentially detect the discrete flight details of two birds at a time.

The findings of the study are slated to appear this month in the journal Integrative and Comparative Biology.

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