EXPONENTIAL INCREASE OF THE DALMATIAN PELICAN (PELECANUS CRISPUS) POPULATION IN THE KURGAN AND TYUMEN REGIONS

摘要

In the 1930-1960's, the only breeding site of the Dalmatian pelican (Pelecanus crispus) in Western Siberia (within the borders of Russia) was Lake Chernoe located at the border between the Kurgan and Tyumen regions. In the 1970's, the species started breeding on two more lakes in the Tyumen Region: Bolshoe Beloe and Tundrovo. From the mid-2000's, another two lakes became sites for the species' breeding: the lakes Malye Donki and Manyass in the Kurgan Region. At the end of the 20th century, 100 and more pairs bred on each lake every year and smaller colonies lived on some other lakes. The total number of the species amounted at that time to 300-400 pairs. In 2004-2012, the number of Dalmatian pelicans reached already 600-800 pairs. These estimates are partially reconstructed, as there has never been a year when a bird census would be accomplished in all of the regional colonies at once. On 1-6 May 2017, we did a pelican census using drone aircraft on all lakes where large pelican colonies had been found. The highest number of occupied nests (430) was found on Lake Tundrovo; Lake Manyass - 243 pairs; Lake Chernoe 170 pairs; Lake Bolshoe Beloe was only inhabited by 7 Dalmatian pelican pairs. As regards Lake Malye Donki, no pelican colony was found there. Thus, the total quantity of occupied nests amounted to 850. Up to 50 more mature pairs might not have had the time to build nests and lay eggs by the first decade of May when we did the census. Nowadays, the region is a breeding territory for about 1/7 part of species' population in the world. Over the past 50-70 years, the region's population has been increasing exponentially; this being evidence of the conditions favourable for the species. The most probable of these conditions are: 1) the global climate warming continuing over the past decades and causing the aridization of more southern areas which drives the birds into the northern part of their distribution area; 2) the extension of the frost-free period of the year connected with the climate warming which allows the birds to start the breeding season earlier and finish it later; 3) the lack of human disturbance as the waterbodies concerned are located in nature conservation areas and are very rarely visited by people. Apparently, neither oscillations of the waterbody filling level nor fish abundance fluctuations render a significant impact upon pelicans due to their capability of far-distance feeding flights. This study was performed in the framework of a state contract with the Institute of Plant and Animal Ecology, Ural Branch, Russian Academy of Sciences, partly also supported by project no. 15-12-4-28 of the Ural Branch of the Russian Academy of Sciences.