Birds migrate at night in scattered flocks

A recent analysis indicates that birds do not fly alone when migrating at night. At least some of them go together in their migration journey, they still fly together even when separated from each other by 200m or more.

Research conducted by the University of Illinois and the Illinois Natural History Survey was published this month in Integrative and Comparative Biology. This is the first study to confirm by statistics what the ornithologists and observers have long suspected: birds fly together in discrete flocks during their night migration.

Researchers have spent decades trying to identify migratory birds at night - the time when most migrations take place - how. But tracking traces of small-sized flying trails at night with a height of ¼ miles to 1 mile is not an easy task. They had to use stop beams, radar lights, and a wide-range radda to know the course of the night's journey. Some even saw birds flying across the moon.

Over decades of meticulous observation, Ronald Larkin, the research leader and animal biology professor, conducted the study with Robert Szafoni - learned that birds fly together at night but do not follow the flock. crowded like daytime. Larkin is also a wildlife ecologist working for the Illinois Natural History Survey (INHS) where Szafoni plays a research scientist. Szafoni is currently a member of INHS.

Ronald Larkin and his colleagues used a low-density Korean surveillance radar from Korea to detect and record the details of individual birds' flights at the same time.He said: 'Whenever the bird flies, the radar will point towards it.' (Photo: Brian Stauffer, University of Illinois News Bureau)

According to Larkin, previous studies 'sometimes assert that birds fly 10 meters apart but somehow they remain grouped together'. But evidence proves 'indirect and suggestive.'

Even if there is a hypothesis that birds fly together, no one will know if they are swarmed into a passive group or they actively fly together.

In the new study, scientists have access to new bird flight information that Larkin has collected from the 70s and 80s using low-power tracking radar. The radar emits microwaves in a narrow cone - a pencil that can point to any object within a defined range.

Larkin said: 'If a bird becomes a target, we can see it through the radar signal. Just turn the button, it will circle the target, keep track of the target even if the bird flies all the way to the radar.

The radar tracks the target distance (calculated from radar), altitude as well as the direction of movement at all times. It also provides data for calculating the target's flapping frequency. Because the radar can also track flying insects or other arthropods, wing-beating data is important to distinguish birds and bugs.

To gather data, Larkin and Szafoni and his colleagues used the radar in a new way. Once the radar operator has identified the flying object as a bird, the person will continue to monitor its flight. He also needs to search for other objects within the radar beam. If another potential object appears, the radar can track it for a few seconds before switching to the original target. By traveling back and forth between the two targets, the operator can distinguish the details of the two birds' separate flight at the same time.

According to Larkin, determining whether the two birds actively fly together requires sophistication and skill.

He said: 'Back in the 1970s, it was clear that two birds flew parallel to each other from the same direction at the same height, but they flew at different speeds, one chasing after the other. They are just like cars on the highway. They simply go along the same path but don't go together. '

Similarly, two animals can go at the same speed but with slightly different angles to each other.

'After only a while they were miles apart'. This is clearly proof to prove that the birds do not fly together.

After analyzing a lot of experiments, the researchers determined that the proportion of significant migratory birds they had tracked flew at the same altitude, at the same speed and in the same direction. Some of the pairs of birds are relatively far apart, about 200 meters - this is close to two football pitches - but they still fly together.

In order to determine whether the birds were swarmed by the wind in a passive manner or that they actively flew into groups, the scientists analyzed the flight pattern of insects and other arthropods flying in the same space. at the same time as the birds. These tiny creatures are left to the wind, which has led researchers to get a reliable picture of airflow patterns.

The analysis above demonstrates that birds follow their own path and are not simply swept by the wind.

Larkin said: 'For me, this is interesting. Birds fly in mid-night flocks in the sky through territories that they have never been to before. '