Study of migratory birds

The task of studying migratory birds was almost impossible to solve until the beginning of the age of small satellite transmitters. Of course, people knew that the birds were flying away somewhere for a while. And how many of them, where, with what stops and routes remained a mystery. What added to the intractability of the task until the 21st century was that birds literally flapped their wings at all human borders: they live in Italy, winter in Egypt or Turkey, and cross any regions.

But the age of affordable satellite Internet, navigation with an accuracy of up to 10 meters, small receivers, location signal transmitters, good but not heavy lithium batteries, and even the most compressed power consumption of devices have arrived.

As a result, birds began to be studied comprehensively in terms of migration, such as the Egyptian vulture. But this is no longer a job for some genius or institute or country. The whole world is needed here. The list of scientists for one study is off the charts – 40 people, these are just the specialists themselves, and they all had assistants.

The vulture is extremely fond of different countries. As a result, each individual individual studied could fly anywhere from 28 countries of the world; the total range includes even more so 44 countries.

Now the numbers. 94 birds were captured and equipped with transmitters. The study involved 11 separate scientific teams; they worked in Albania, Armenia, Bulgaria, Ethiopia, France, Greece, Israel, North Macedonia, Portugal, Russia, Spain and Turkey. The ranges of the tagged individuals extended over 4,000 km from the Iberian Peninsula to the Caucasus region in Western Asia. And 4000 kilometers from Southern Europe to the Sahara.

The weight of the transmitters is from 24 to 45 grams, which is 35 of the body weight of the Egyptian vulture. They were attached through the “backpack + belt system with leg loops.” GPS fixation data frequency varied from one signal per minute to two hours. The accuracy of bird location is ± 18 meters.

The birds were chosen at different ages: from young ones, with little or no flight experience, to older ones, with a lot of experience.

Data from the sensors was uploaded to the online repository movebank.org, and erroneous location determinations were removed using general-purpose data filters. The error radius is set to 30 meters. In total, 188 complete migrations were calculated and verified: 71 spring and 117 autumn.

General conclusions of the study:

1. The subpopulation from the Balkans overlapped during wintering with the subpopulations of the Middle East and the Caucasus. And so with other subpopulations – birds constantly flew to other people's wintering grounds, which ultimately ensures active mixing of genetics within the species, eliminating dangerous inbreeding.

2. The onset of migration varies by a month or more among the different birds of this species studied in this study.

3. Adults migrated better and faster, flying to wintering grounds along more direct routes. Young people are worse. Learning is to learn from each other, plus personal experience gained through hunger, thirst and possible death. There is no mega-map inside the birds’ heads, they are taught by the individuals around them, they just need to repeat what is happening. That same instinct also plays a big role. This does not mean that at the appointed hour a 3D map lights up in the bird’s head and the requirement to fly to such and such a point, as on the Yandex map. Over thousands of generations, hormones have undergone natural selection so that they act on birds as they do on cats. The bird simply flies after its species, and if there is no one nearby, it rushes about and also flies. Solitary birds flying for the winter worry in the same way as flocking birds.

4. It has been shown that migration itself constantly encourages people to try new places for wintering and return routes afterward. During periods of migration, birds periodically fly to different places, which stimulates the mixing of different genetics.

Here is the basic article for the first part.

The second example of mass research of migratory birds. The object of the study is the harrier bird of prey. Circus pygargus . For the reasons described above, before the age of satellite positioning, ornithologists relied only on bird banding, which is very labor-intensive: literally hundreds and hundreds of birds of each species must be banded and this does not provide any guarantee that the bird will be seen by anyone again.

The study involved 34 adult harriers and tracked them through six migrations, from 2005 to 2011. Harriers were caught to be equipped with sensors in Denmark, Germany, the Netherlands, Poland, and Belarus.

All individuals were caught near the nests. They were released 40 minutes after capture. The transmitters were secured with 6 mm thick Teflon tape. Solar satellite transmitters weighing from 9.5 and 12 grams were used – PTT-100 series, Microwave Telemetry Inc., Columbia, MD, USA. The transmitters are programmed for two on-off cycles of 10–48 and 6–16 hours. Data from them were obtained through the ARGOS system, Toulouse, France. 47,000 corrections were made during information processing. A total of 104 migration tracks were obtained, 17 of which were incomplete due to the death of the bird or sensor failure. A Mantel test to quantify the strength of migration ties was conducted using the R package 'ade4', in which the statistical significance of the Mantel correlation coefficient was determined using 9999 random permutations.

General results – birds are conservative in choosing a migration route, depending on the place of birth. Those born in the western breeding population migrated 78% of the time along the western route and 22% of the time along the central route; no birds flew along the eastern route. Of the two birds of the central breeding population, one male migrated westward, and one female migrated centrally. All individuals of the eastern breeding population migrated via the eastern route.

Basic article.