Number dynamics of the White Stork in Ukraine in 1994–2003. - V.N. Grishchenko. - Berkut. 13 (1). 2004. - P. 38-61.
White Stork is a convenient species for the analysis of patterns of population dynamics. Moreover, reasons of general and synchronous number increasing remain in many respects not clear. In Ukraine number dynamics of the species is influenced by two factors during many years: general changes in numbers and continuing expansion of the White Stork to the east. Therefore trends differed in east regions and in other parts of the country. In Ukraine in 1992 has started the program of monitoring of the White Stork population. Ornithologists and voluntary helpers take part in observations. Data are obtained on the net of constant study plots in different regions. They let control breeding success and number dynamics in the country. In total the information from 134 plots in 22 regions of Ukraine is obtained in 1992–2003. On 63 from them observations were carried out during 3 and more years, on 15 ones – during 10–12 years, on 1 – 17. Since 1994 the obtained data are sufficient for the analysis of number dynamics. Considered ten years cover the period between Vth (1994–1995) and VIth (2004–2005) International White Stork Censuses. For the analysis of population dynamics the average increment of numbers on study plots in % were used. Since 1994 the increase of number permanently rose (Fig. 1). Maximum of increasing was registered in 1996 and 1998. In 1997 number of the White Stork has sharply decreased. This year was catastrophic for the species almost in whole Europe. It was caused by bad conditions during wintering and spring migration. Already the next year population was completely restored and number increasing continued. Since 1999 rate of growth began to decrease and last years population was stabilized. Comparison of dynamics of number increasing in three large regions of Ukraine (Fig. 2) shows that this process has firstly started in North-East Ukraine, the greatest increase of number was registered also here. In 1994–1998 numbers changed in all three regions synchronously. Later this synchronism was reduced and last years changes went discordantly. Ceasing of number increasing after 2000 was registered also in other countries, for example in Germany. Expansion of the White Stork has wave-like pattern. One of such waves in fact was traced during the period of observations. This wave has started in Ukraine with number increasing early in 1990s. Enlargement of the breeding range was observed in east regions of the country. At the same time the expansion livened up in Russia. General questions of expansion and number increasing of the White Stork are discussed. In Ukraine the number increased first of all and to a greatest extent in optimal habitats with low population density. Expansion of the White Stork in East Europe can be considered as filling of “faunistic emptiness” remaining in North Palearctic after the last glaciation. The expansion is vectorial. In East Europe it goes to the east, a lesser degree – to the north, but not to the south. This phenomenon can be connected with genetic determination of direction of young birds dispersal in population near the east border of the breeding range. Such “directed” population can be formed by the natural selection. Mechanism is similar to genetic control of partial migration well studied by P. Berthold and colleagues. If different directions of dispersal are equal for the population, existing various genetic programs of dispersal will remain in the same ratio. But if one of the directions give a preference in breeding success, the part of birds with this variant of the program will increase. “Vector of expansion” can be predetermined also by other factors. For example, dispersal goes on the way of “minimum resistance”, on areas having favourable conditions for breeding but with low population density of storks or full absence of them. At last, combination of endogenous and exogenous control of dispersal is possible. Breeding success of the White Stork is higher in east part of the breeding range: in Ukraine (the Dnieper area and eastwards from this river) and in many regions of Russia. This fact explains a well known contradiction: storks continued advance to the east in spite of number decreasing of the species and depression of populations in many countries. The east part of breeding range are all-sufficient for the expansion: high breeding success and predominant direction of dispersal create the necessary prerequisites for further moving eastwards in spite of the situation in other parts of the breeding range. In Ukraine the negative correlation between population density and breeding success of the White Stork was not found. Probably ecological capacity of environment is far from the saturation and population density is not a limiting factor. It creates prerequisites for further number increasing. Only on one large area in Ukraine considerable number decreasing of storks was noted: they almost stopped breeding in Chernobyl exclusion zone in 1990s. But it is connected not with population trends. This area became unsuitable for the White Stork because of evacuation of people and desolation of agricultural lands. Close correlation between changes of numbers and breeding success was found (Table 2). It means, that dynamics in both cases are caused by the same factors. First of all these are conditions in wintering area. Their influence on eastern population of the White Stork is discussed. It is supposed that reasons of its rise are also connected with African wintering grounds. May be global climate changes in Africa have caused the improvement of food supply for wintering storks. It promoted increasing the survival rate and breeding success and was an impuls for synchronous changes in numbers on the territory of whole breeding range of the European subspecies. Number of White Stork in Ukraine in 2003 is estimated at least in 25000–30000 breeding pairs. [Russian].
Key words: White Stork, Ciconia ciconia, Ukraine, number dynamics, breeding range, expansion, dispersal.
Address: V.N. Grishchenko, Kaniv Nature Reserve, 19000 Kaniv, Ukraine; e-mail: vgrishchenko@mail.ru