Long-term monitoring of the European roller (Coracias garrulus) in Ukraine: is climate behind the changes?

Abstract

The European range of the roller was formerly more extensive, but since the 1980s there has been a long-term decline in numbers and in range, particularly towards the north, including much of north-western Ukraine. Our specific goals were to reconstruct the environmentally suitable range of the species in Ukraine before the 1980s, gain better knowledge on its requirements, compare the past and current suitable areas, infer the regional and environmental variables that best explain its occurrence, and quantify the overall range change in the country. For these purposes we created a database consisting of 584 findings made in Ukraine, based on a lengthy record of occurrences extending back to 1851: 203 for the period prior to 1980, 91 for records made between 1985 and 2009, and 290 records made between 2010 and 2020. We employed a species distribution modelling (SDM) approach to hindcast changes in the suitable range of the roller during historical times across Ukraine and to derive spatially explicit predictions of environmental suitability for the species under current climate and a set of factors that were hypothesised to be of importance to roller presence and securing a sufficient food base. SDMs were created for three time intervals (before 1980, 1985–2009, 2010–2020) using corresponding climate data. SDMs show a decline of suitable for rollers areas in the country from around 86 to 44%. Several factors, including land cover and land use, human population density etc. that could have contributed to the decline of the species in Ukraine, were considered. For example, the loss of area of ‘short vegetation’ appears detrimental, although recent gains in this respect have favoured the bird in the Chornobyl Exclusion Zone and around, where Landsat images show the change from a previously vibrant agricultural and forestry economy, when crops have been replaced by grasslands. Threats posed to the roller by habitat and land use change are also likely to be compounded by the effects of global climate change. In summary, we suggest climate change, in particular velocity, have been responsible for shaping the contemporary home range of the European roller in Ukraine and perhaps beyond.