Putting Britain’s Birds on the Map: Digitising a Landmark Citizen Science Project

Putting Britain’s Birds on the Map: Digitising a Landmark Citizen Science Project

 The British Trust for Ornithology (BTO) holds around 250,000 Common Birds Census (CBC) maps from nearly 1,500 sites, recording UK bird population data collected by citizen scientists between 1962 and 2000. In 2023, a TownsWeb Archiving Digitisation Grant supported BTO in digitising maps and habitat notes from a single site — a pilot project laying the groundwork for digitising the full collection, potentially ahead of BTO's centenary in 2033.

In 2023, we were delighted to award a TownsWeb Digitisation Grant to support the British Trust for Ornithology to digitise one of the UK’s most important historical bird monitoring resources: the Common Birds Census maps. These fragile archival maps record decades of observations by citizen scientists and provide a unique dataset on UK bird populations from 1962 to 2000. By undertaking digitisation, BTO preserved this invaluable resource while making it widely accessible for researchers, conservationists, and the public.

We spoke with Lesley Hindley, BTO Archivist, to understand more about the material.

Running from 1962 to 2000, the CBC monitored the numbers of common breeding birds across the UK through a nationwide network of dedicated volunteers. Each year, birdwatchers visited their chosen site ten times during the breeding season, carefully recording what they saw and heard.

Using detailed 1:25,000 maps, observers plotted the location of each individual bird and recorded species codes alongside notes on behaviour and activity. Over time, these observations built a remarkably detailed picture of bird populations across the country.

“These maps form a unique resource which provides the only national information about the UK's birds over the period 1962 to 2000.”

- Lesley Hindley, BTO Archivist 

Today, the British Trust for Ornithology holds approximately 250,000 CBC maps from nearly 1,500 sites, making the archive one of the most significant long-term datasets on British bird populations.

Why Digitisation Was Needed

Digitisation was needed because the CBC maps are large-format sheets drawn on fragile tracing or thermal paper, viewable only at BTO's Thetford headquarters, putting them at ongoing risk of damage through handling.

Despite their value, the physical maps presented significant challenges for preservation and access. Many of them are large-format sheets created on tracing or thermal paper - materials that become fragile over time and are vulnerable to damage through handling.

“The maps are large and can only be viewed at our headquarters in Thetford, Norfolk. As well as being unwieldy, they were drawn onto tracing or thermal paper which makes them fragile and puts them at significant risk of damage through handling.”

 - Lesley Hindley, BTO Archivist  

Digitisation offered a way to both protect these important materials and unlock the data within them. For this project, the BTO team chose to digitise the maps and accompanying habitat notes from a single site, creating a representative sample of the wider collection.

Working with a smaller subset allowed the organisation to test the most effective approach to capturing and managing the information contained within the maps.

Laying the Foundations for a Bigger Project

While the initial digitisation focused on a single site, the knowledge gained from the process is already shaping a much more ambitious vision for the future of the CBC archive.

The long-term aim is to digitise and open up the wider CBC collection - potentially in time for BTO’s centenary celebrations in 2033.

A Collaborative Process

The project was carried out in collaboration with TownsWeb Archiving, with close communication throughout the process. Shortly after the grant was awarded, a member of the TownsWeb team visited BTO’s headquarters in Thetford to review the materials and discuss the logistics of digitisation.

The maps were then delivered for digitisation at the start of 2024, with regular updates provided throughout the project.

“We were kept updated by email throughout the digitisation process, and appreciated the communications checking on conventions for naming files or before taking action such as removing staples.”

 - Lesley Hindley, BTO Archivist  

Once completed, the original materials were returned and the digitised files delivered to the team, ready to begin the next phase of work.

Unlocking the Potential of the CBC Archive

Perhaps most importantly, the project has helped to refocus attention on the enormous potential contained within the CBC collection.

With BTO’s centenary approaching, the organisation is now exploring funding opportunities and developing plans for a much larger initiative to digitise the collection and unlock the data it contains.

The goal is to unlock these data to address nationally important questions about how and why bird populations have changed over time - insights that are increasingly vital in the context of biodiversity loss and environmental change.

What began as a small-scale digitisation project has become the starting point for reimagining a unique scientific resource for the digital age.