Climate change is impacting wild populations, but its relative importance compared to other causes of change is still unclear. Many studies assume that changes in traits primarily reflect effects of climate change, but this assumption is rarely tested. This paper uses datasets from across Europe, including the BTO's Nest Record Scheme, to show that in European birds global warming was likely the single most important contributor to temporal trends in laying date, body condition, and offspring number. However, non-temperature factors were also important and acted in the same direction, implying that attributing temporal trends solely to rising temperatures overestimates the impact of climate warming. Differences among species in the amount of trait change were predominantly determined by these nontemperature effects, suggesting that species differences are not due to variation in sensitivity to temperature.

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.

Rotational burning of vegetation is a common form of land management in UK upland habitats, and is restricted to the colder half of the year, with the time period during which burning may be carried out in upland areas varying between countries. In England and Scotland, this period runs from the 1st October to 15th April, but in the latter jurisdiction, permission can be granted to extend the burning season to 30th April. In Wales, this period runs from 1st October to 31st March. This report sets out timing of breeding information for upland birds in England, Scotland and Wales, to assess whether rotational burning poses a threat to populations of these species, and the extent to which any such threat varies in space and time.

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.

This report presents the main findings from survey work delivered using passive acoustic monitoring devices deployed across the Bailiwick of Guernsey in 2021, the first season of the Bailiwick Bat Survey, including the first extensive baseline data for bats for the islands of Guernsey, Alderney, Herm and Sark.

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.