Volunteers provide vital new information on the UK's breeding Tawny Owls

Volunteers provide vital new information on the UK's breeding Tawny Owls - BTO

Tawny owl sitting in a tree (Liz Cutting) — (Liz Cutting)

Thanks to the efforts of nearly 10,000 'citizen scientists' we now have a much greater understanding of the UK's breeding Tawny Owls, together with much-needed information on their calling behaviour, that will help future surveys of the species. The results of this study have just been published in the journal Bird Study.

Despite being reasonably common, widespread, and easily identifiable from its vocal behaviour, we know surprisingly little about the changing fortunes of the UK's breeding Tawny Owl population. There is evidence for an ongoing but shallow long-term decline in the population since the mid-1980s, but this evidence comes from studies that involve daytime surveys by volunteers. Better information is likely to come from dedicated surveys, carried out at night during the Tawny Owl’s breeding season, when territorial vocal activity is at its peak.

Such dedicated surveys typically rely on the use of call playback to elicit responses from territorial birds, a labour-intensive method that limits survey coverage. An alternative approach has been tested using nearly 10,000 volunteer 'citizen scientists' and the results are extremely encouraging. The BTO Tawny Owl Calling Survey set out to establish the factors that influenced Tawny Owl calling behaviour (such as weather conditions and local habitat) and to determine whether the approach could reveal changes in Tawny Owl populations over time.

The BTO Tawny Owl Calling Survey was carried out over two separate survey periods (October to March in 2005/06 and 2018/19) and had a particular focus on the impact of urbanisation. Volunteers carried out surveys across each winter period, avoiding evenings that were wet, windy or had poor visibility. They were asked to record whether they heard Tawny Owls calling during the survey period, and to specify the types of Tawny Owl calls heard. The volunteers also collected data on the amount of cloud cover, which was used alongside environmental data from other sources to identify factors that might influence calling behaviour.

Some 9,452 volunteers took part in the survey in 2018/19 and 3,465 took part in 2005/06, collectively covering 9,567 sites. Overall, Tawny Owls were reported at least once from 86.8% of sites in 2005/06 and 84.3% of sites in 2018/19, suggesting that Tawny Owl populations have been largely stable over this period.