Data collected from volunteer bird bells operating Constant Effort Scheme (CES) sites for the British Trust for Ornithology (BTO) provides insights into the numbers, breeding success and survival rates of 24 common resident and migrant songbirds. How did these species fare in 2020? It has been suggested that birds may have benefited from the decrease in human activity in most of the British and Irish landscapes in the spring and summer. While some birds that are particularly vulnerable to disturbance, such as coastal waders and terns, thrived in some locations, the evidence generated by CES rings suggests that it was indeed a bad breeding season for many of our smaller birds.
Spring was one of the warmest in history, but perhaps counterintuitively, it wasn’t necessarily good news for all bird species, as Lee Barber, the BTO’s Demographic Surveys Officer, explains. “In warm springs, caterpillars hatch earlier and develop faster. Birds also lay their eggs earlier, but not to the same extent, and so food availability peaks before the time when their young are most in need of it, resulting in fewer fledglings. Our wrestlers’ results show that the average number of juvenile blue and great tits caught per adult in 2020 was lower than any other year since the survey began nearly 40 years ago. “
Willow Warbler, Copyright Glyn Sellors, from the Surfbirds Galleries
Garden Birdwatch (GBW) development officer, Rob Jaques, said Ringers weren’t the only group of BTO volunteers to experience a shortage of tit species in the UK in 2020. “The participants in the BTO’s Garden BirdWatch survey reported that blue and great tits come from fewer gardens than average in summer. Data from CES wrestlers suggests the number of adults in 2020 was above average. The decrease in GBW observations therefore most likely reflects the poor breeding season. “
On the positive side, some of our summer visitors did well in 2020, with the number of returning migratory birds well above average. Lee notes that “the incidence of Chiffchaff and Blackcap, two short-haul migrants this winter in southern Europe and north Africa, was the highest since surveillance began in 1983, and the number of declining willow warblers was also above average.”
For many volunteers, such results have been a real boost, explains Dave Leech, director of the doorbell program. “It’s been a tough year for everyone across the country. In many areas, ringing was impossible due to restrictions imposed in response to the Covid outbreak. However, the spring lockdown in England ended shortly after the start of the CES period in May, and about half of all locations were able to provide data that year. Our wrestlers invest a lot in monitoring our birds and this opportunity to engage with nature in such a positive way has really helped them tackle the challenges of 2020. “