Monitoring of the Number of the Spoonbill (Platalea leucorodia L.) in Rostovskii Nature Reserve and the Dependence of Its Reproduction on Environmental Factors

Abstract

The flooding of the Western Manych River in 1948–1954 caused the formation of the modern aspect of Lake Manych-Gudilo. This exerted a positive effect on the limnophilic complex of birds. In the 1950s, the authors of the article observed the proliferation of the European pelican (Pelecanus onocrotalus L.) and the Dalmatian pelican (P. crispus Bruch), the Caspian gull (Larus cachinnans Pall.), the spoonbill (Platalea leucorodia L.), and other species. Their numbers increased in the 1960s–1980s. The fresh water supply resulted in the development of livestock farming, the plowing of steppes, and anthropogenic desertification. In 1995, the Rostovskii Nature Reserve was established. The authors actively participated in its creation and zoological research. Bird watching was regularly performed. The aim of this article is to analyze changes in the number of colonial limnophilous species, nesting in the reserve, including the spoonbill, and the factors of their fluctuations. Data on the number of all nesting colonies of birds, the number and distribution of nests and eggs, relationships, etc. are given. The creation of the reserve exerted a positive impact on the avifauna. About 120 pairs of spoonbills bred here between 1995 and 1998. The modern complex of water birds differs greatly from that of the 20th century, which is associated with environmental changes. The increase in water mineralization in Lake Manych-Gudilo and other reservoirs led to the disappearance of reed beds, fish, and many other organisms and to a profound restructuring of aquatic and near-aquatic biota. Climate aridization of the 21st century exerted a strong impact on wildlife and resulted in the partial or complete drying up of reservoirs, a drop in the water level in the lake, and the disappearance of colonies of limnophilous birds, where the spoonbill bred (the last one disappeared in 2023). In recent decades, the lands around the reserve are actively used in agriculture. The wide use of pesticides outside the reserve with disregard for regulations and violations of the technology for their use negatively affects many animals. The most important defenders of polyspecies colonies from foxes and other predators that periodically penetrate there are represented by Caspian gull, which feeds in the fields. By consuming poisoned organisms, seagulls die themselves and poison their chicks with this food. In 2021–2023, a mass die-off of birds was observed in the area of the last multi-species colony of birds; in 2024–2025, the colony disappeared, and several foxes lived on the island.