Chronicle of the disappearance of the Yellow-breasted Bunting (Emberiza aureola, Emberizidae, Passeriformes): Spatial structure and population dynamics

Due to a sharp decline in numbers, the Yellow-breasted Bunting (Emberiza aureola) is listed as a threatened species on the IUCN Red List. Formerly an abundant inhabitant of meadows, it disappeared as a breeding species in Central Siberia in a short period between 1999 and 2006. We studied breeding density, habitat use, spatial structure and population dynamics of the Yellow-breasted Bunting population in the Yenisei middle taiga since 1978 in the years preceding the decline, and further on. The species showed a narrow specialization in the choice of habitats and occupied rare isolated patches of open habitats in taiga. Most breeding habitats were regularly populated at high densities, reached saturation and indicated a prosperous state of the population. Annual deviations in population size were small and were determined by wintering conditions. Regulation of numbers occurred at breeding sites through strict territorial relationships depending on density. In accordance with the model of ideal despotic distribution, excess individuals in years of increased abundance were displaced to habitats that were unsuitable for reproduction. This distribution was achieved independently in each isolated group of suitable habitats, and the exchange of individuals between groups was minimal. The noted population characteristics, together with the distinctive features of the subspecies E. a. aureola, suggest a long-term dependence of the ecology and dynamics of Yellow-breasted Bunting on the history of rice cultivation in Southeast Asia. The use of anthropogenic food resources in winter was likely reason for both previous expansion and modern decline in numbers due to changes in agricultural technologies. The millennial use of additional winter resources changed the parameters of the species’ life history in the direction of “slow life,” which did not contribute to the formation of adaptations to the conditions of the expanded range in the taiga zone. The current decrease in the availability of winter food has devalued the acquired changes and led to the collapse of the population. The extermination of birds in wintering grounds significantly accelerated the decline in numbers, but was hardly its main cause.