On our webpages we repeatedly raised the question of studying migration of birds of prey using satellite telemetry. This method has pluses and minuses compared to traditional ringing, colour marking etc. The review makes an attempt to reveal, at least partly, potential opportunities of the satellite telemetry on the example of studying migrations of the Short-toed Eagle.
Some researchers and birdwatchers oppose the direct installation of satellite transmitters on birds basing on ethic reasons. Their main argument: until the absence of negative impacts is proved the method cannot be used in researches. However, it is not an easy task to receive such proofs. It would require control observations of certain types of transmitters and certain bird species and further processing of results with the use of statistical analysis to minimize as much as possible the effect of random factors. Firstly, the sample of birds should be large enough for such processing, which means installation of a lot of transmitters, secondly we must conduct parallel observations of the control bird group without transmitters attached. But exactly the latter is impossible since nowadays there are no other effective methods designed for long-term tracking of birds in their natural environment. In addition, installation and monitoring of even a single transmitter is still fairly expensive, not to mention their dozens. This fact puts restrictions on the use of this method in favour of its opponents.
Below there are data on the size of breeding populations of Falconiformes and Strigiformes of Ukraine (table). If have a look, they prove that numbers of many raptors go on declining. Compared to the previous one (Red Data Book of Ukraine, 1994) the new edition (Red Data Book of Ukraine, 2009) additionally added two species of Falconiformes and Owls. Numbers of eight species don’t exceed several dozens of pairs. Two species (Red Kite и Pallid Harrier) stopped breeding in Ukraine, another two (Osprey и Lesser Kestrel), are also obviously extinct.
For the last 15 years increase of numbers was noted for 6 species of Falconiformes, while 5 species have decreased, and 5 have a stable population; as for the other, their trend isn’t possible to estimate since they stopped breeding or breed only in few quantity.
Quite a great reduction of numbers has been recorded for the Black Kite, Montagu’s Harrier, Spotted Eagle, Levant Sparrowhawk и Lesser Kestrel. Increased numbers have the Long-legged Buzzard, Imperial Eagle, White-tailed Eagle, Saker и Peregrine Falcons. Stable, with small fluctuations, are populations of the Short-toed Eagle, Booted Eagle, Lesser Spotted Eagle, Golden Eagle, Black Vulture и Griffon Vulture.
As for Owls, growth of numbers was registered for the Eagle Owl, Ural Owl and Great Grey Owl. Trends of other Strigiformes are hard to estimate reliably because these birds are poor studied.
Seasonal migrations are an important stage in the annual life cycle of birds. They are characteristic for most species of Ukrainian birds of prey. However by the present time migratory routes and sites of mass concentrations are still poor known. Except for scientific importance this knowledge is essential for planning and organization of conservation of birds of prey. Also, sites of mass migration are of obvious interest for all birdwatchers.
Nowadays, the majority of migrants in Ukraine is considered to pass the country by a wide front, though with the reservation accepted that migrations pass not evenly everywhere but mainly follow “ecological routes”, or, at least, ecologically favorable places (Sevastyanov 1992). Therefore migration of birds of prey can be observed over all the territory of Ukraine. However its intensity differs in different regions and separate places.
There are several reasons of it. Birds with specific trophism (the Osprey, White-tailed Eagle) have to keep usual habitats, and for them migratory “corridors” are expressed more distinctly. Thus, the White-tailed Eagle and Osprey in Ukraine can be much more often met along the Dnieper and other large rivers. However even for these species a part of individuals flies during migration time over all the territory of Ukraine.
The more eurytropic are migrants in terms of their trophism, the more similar to the continuous is their migration front. Thus, the majority of birds of prey pass the country in a broad front. The narrowing of their front of migration is caused by landscape or weather and climate barriers.
To analyze the intensity of migration of birds of prey in the territory of Ukraine we have used the data on the maximum number of the individuals met for one day at one observation point during autumn migration (picture).
Despite small quantity of the data, results confirm that the migration goes by a broad front. Essential influence on the migration intensity is caused everywhere by weather conditions. In peak days of passage the number of migrants can increase in dozens times.
There came a period of bird spring migration, and again we’re searching the sky for silhouettes of our favourites. Quite often we don’t guess that our observations might give an unexpected result. During last decades an individual marking of birds of prey by using colour rings, wing tags or ‘windows’ on wings is rather common-spread. These are the elements which should be paid attention when observing birds, also during migrations. A camera may be very useful as modern technical devices give a possibility to take a picture of a bird, and then have a better look at necessary features. Therefore we can advise not only gaze at flying birds, but take a picture.
First three photo are taken from the paper: Dravecký M, Sellis U, Bergmanis U, Dombrovski V, Lontkowski J, Maciorowski G, Maderič B, Meyburg B-U, Mizera T, Stój M, Treinys R & Wójciak J 2008: Colour ringing of the Spotted Eagles (Aquila pomarina, Aquila clanga and their hybrids) in Europe – a review. Slovak Rapt J 2: 37–52.
The colour marking of birds in Ukraine was not provided yet, but basing on migratory routes, you can meet the raptors marked in other countries, as follows: