The national Dartford Warbler, Woodlark and Nightjar surveys

Heathland, Sam Turley (rspb-images.com)

Few wildlife experiences in the UK can rival the atmosphere of a summer visit to lowland heathland at dawn or dusk. In 2025, more than 1,200 birdwatchers from across the country came together to survey three species, associated with, but not confined to lowland heathland: Dartford Warbler, Woodlark and Nightjar (the latter is not an RBBP species). A heartfelt thank you goes to everyone who contributed.

These surveys, collectively known as the Heathland Bird Surveys, were a partnership project between the RSPB, the British Trust for Ornithology (BTO) and Natural England. After analysing the data over winter, the early results are encouraging. Compared with the last national surveys (conducted in 2006 for Dartford Warbler and Woodlark, and in 2004 for Nightjar), the number of territories recorded has increased by 27% and 29% for Dartford Warbler and Woodlark respectively, while Nightjar numbers have risen by around 20%. Both Woodlark and Nightjar have also expanded their range, with Nightjar now breeding more widely, including increasing numbers in Scotland.

Woodlark, Colin Bradshaw

Data submitted to the RBBP plays a crucial role not only in tracking trends in rare and scarce breeding birds, but also in designing national surveys such as these. For this project, RBBP records helped identify 1 km survey squares with recent sightings, ensuring priority was given to the most important areas.

Current provisional estimates suggest the UK population of Dartford Warbler stands at about 4,100 territories. Most birds remain concentrated in traditional lowland heathland strongholds in southern and eastern England, such as Dorset Heathlands, Thames Basin Heaths, the New Forest, Wealden Heaths and the Suffolk coast. The survey only detected limited range expansion outside areas occupied during the last survey in 2006, with no evidence of further increases at higher elevations.

This updated estimate exceeds the RBBP’s guideline threshold of 2,000 breeding pairs. The Panel regularly reviews the list of species it covers, and some species with higher populations are retained if RBBP data still provide reliable annual totals or if alternative surveys are unable to support the calculation of population trends. Dartford Warbler was retained on the RBBP list after the 2006 survey (which estimated around 3,200 territories) due to its vulnerability to sudden declines during severe winters; its status as a RBBP species will be reviewed by the Panel in due course.

Dartford Warbler, Les Cater (rspb-images.com). Unlike many warblers, this species is resident in the UK and has benefited in recent decades from milder winters and targeted and effective habitat management of lowland heathland.

Climate change is also an important part of the story. Although Dartford Warbler numbers have increased overall since 2006, RBBP data indicates that populations dropped following the cold winters of 2008/09 and 2009/10. A sequence of milder winters, since then has enabled recovery. This species is particularly sensitive to prolonged cold and snow cover, especially at the northern edge of its range in the UK.

Looking ahead, climate projections suggest the Dartford Warbler’s global range will shift northwards and eastwards. While a warming climate may favour the UK population (assuming suitable habitat remains available), it is likely to have negative effects elsewhere. By the end of the 21st century, more than 60% of its current range, particularly in Spain and Portugal, which hold the bulk of the global population, could become unsuitable. Across Europe, the species has already declined by over 50% since the late 1990s. Additionally, climate change is expected to increase the risk of wildfires in key breeding habitats.

Lowland heathland is one of the most threatened habitats in the UK with 80% lost since the 1800s, mainly due to land use change, including forestry and (e.g. urban) development. In response, considerable effort has been invested in its heathland restoration and appropriate management. The results from the national survey are testament to the impact of all this hard work.

Regular national surveys like these are essential for understanding how species are faring. Until now, assessments have relied on data that is up to two decades old. The new findings will play a vital role in evaluating the effectiveness of Special Protection Areas, informing Site of Special Scientific Interest (SSSI) condition assessments, and understanding the pressures posed by climate change, recreation and development.

Finally, sincere thanks go to everyone involved: the volunteers who carried out the fieldwork, the BTO’s regional organiser network, county bird recorders and bird clubs who helped coordinate the survey, and the landowners who granted access. These surveys would not be possible without such collective effort. Funding was provided by Natural England, DEFRA and the RSPB.