BTO staff co-author a rebuttal letter setting out the importance of the careful use and interpretation of citizen science data in estimating avian population sizes.

Like many things, long-term monitoring of bird populations was interrupted during the COVID-19 lockdowns. Here, BTO scientists look at the effects of restrictions on participation in the Breeding Bird Survey during 2020 compared to previous years, and devise analytical methods to overcome the issues that emerged.

Prior to this study, most Tawny Owl population data was collected during daylight surveys for other species, or specialist, labour-intensive night-time surveys during the breeding season. The BTO Tawny Owl Calling Survey, however, harnessed the time and skill of thousands of volunteers to shed light on the impact of urbanisation on Tawny Owl populations, and used the data collected to develop the best methods for surveying these nocturnal raptors in the future.

International collaborative research involving BTO has used data collected 30 years apart, during the two European Breeding Bird Altases, to examine range shifts in wetland birds.

Researchers from BTO and the scientific department of Belarusian Chernobyl analysed 22 years of raptor population data from the Chernobyl Exclusion Zone (CEZ) and identified the impact of reduced human activity on some of Europe’s rarest birds of prey. Their findings demonstrate the power of rewilding for supporting biodiversity, including the conservation of vulnerable species. Over 2,000 km² of Belarus previously given over to intensive agriculture and dense settlements was affected by the 1986 reactor meltdown at the Chernobyl Nuclear Plant in Ukraine. Since then, this area has experienced little to no human disturbance, leading to decades of ‘passive rewilding’ where nature has been left to its own devices. This study explores the effects of this passive rewilding on the bird of prey community inhabiting the area; birds of prey sit at the top of the food chain and are thus excellent indicators of ecosystem health. The authors used a long-term dataset developed from periodic surveys of breeding birds of prey within a 147 km² study plot towards the edge of the Belarusian Chernobyl Exclusion Zone (CEZ). The researchers also used satellite imagery to analyse changes in land cover throughout this period, finding significant shifts in the area occupied by different types of habitat over time. Former agricultural land either became overgrown or rewetted, and the increase in waterlogged areas saw wetland specialists increase in abundance. Two wetland specialist that had been locally extinct in the area prior to the accident – Greater Spotted Eagle and White-tailed Eagle – both returned and increased in number. The study also followed the populations of 12 other raptor species from 1998 to 2019. Different species assemblages – the abundance and type of species present in an area – are associated with different habitats. Analysing the changes in abundance showed a decline in generalist predators, such as Montagu’s Harrier and Buzzard, which hunt over open fields and farmland and eat a variety of prey species, and an increase in specialists such as Greater Spotted Eagles and Hobby. Because some of the specialists are dependent on other important conservation species for food, for example Corncrake and Great Snipe, this change indicates a positive impact of rewilding on the ecosystem as a whole, not just the raptor populations, and shows rewilding’s potential value as a strategy to tackle biodiversity loss.

Mountain and upland regions harbour a high proportion of global biodiversity and have a high rate of endemism, but few assessments of environmental change have been conducted in these areas in compared with more accessible biomes.