Tuning in to the Land 
The Birdsong of Great Chalfield 

In 2024, a major initiative began at the Great Chalfield Estate, marking a new chapter for 140 hectares of Wiltshire farmland. Wiltshire Wildlife Trust secured a 49-year lease in partnership with the National Trust and Great Western Community Forest, committing to manage the land for farming and nature. This project will hopefully become a learning hub for other farmers looking to implement nature-friendly land management. This working farm will demonstrate different land management methods and funding options alongside making space for nature to recover and thrive.   

The changes have been swift, only a few months after the lease was signed, over 11,000 trees were planted across the landscape. These rapid habitat changes are being tracked in tandem with essential baseline surveys, where bioacoustics is playing a key part.  
 
We anticipate seeing a shift in bird populations as our habitat restoration efforts take hold, such as the presence of more hedgerow-dependent species like warblers or seasonal turn of waders in wet features  (when fields flood in winter) and through our acoustic monitoring we are able to track the changes in species.  

Listening to the Landscape 

We started acoustic monitoring for birds at Great Chalfield earlier this year, using eight acoustic monitors, strategically placed to reflect different habitat types across the estate. 

With the rise of bird song recognition software like the Merlin app, the devices generate a vast amount of data. Dr. Aurora Gonzalo spoke to us about the initial findings coming out of Great Chalfield. 

"The data is fascinating," explains Dr. Gonzalo. "We can see clear seasonal changes in bird behaviour, especially around breeding season and when the young are present."  

Key insights from the charts include: 

• Carrion Crow: These birds are more vocal in the morning during the March and April breeding season, peaking heavily around 4-7 AM. They become quieter in June, but toward the end of the breeding period their calls increase again, particularly in the afternoons peak around 6 PM, as fledglings become active and family groups communicate more frequently. 
   

• Eurasian Blackbird: Their calls can get more vocal twice a year, reflecting their tendency to have two broods. Song activity peaks in early March as males establish territories and attract mates for the first brood, then rises again in June when they may begin a second breeding attempt. 
   

• European Robin: Both males and females are vocal, with a peak in activity recorded in May. They are also expected to be highly vocal in winter as they protect their territory—the reason they feature so prominently on Christmas cards. 
   

• Eurasian Skylark: Skylarks are present in most landscape areas but are notably absent from Ladies Coppice. This is expected, as the coppice is woodland, which is not a suitable habitat for Skylarks. 

Future Acoustics 

Our current devices use a single microphone, which allows us to measure richness—whether a type of bird is present in the landscape. Higher-range models feature more than one microphone, to enable triangulation when using more than one device to account for abundance, one of the greatest limitations of bioacoustics. Triangulation will make it possible to identify individual birds rather than just their calls, allowing us to measure not only presence but also the number of individuals detected. 

Verification 

While the bioacoustics data is crucial, it’s important to acknowledge its limitations and the need for verification. 

"The algorithm is good, but it's not perfect, and we have noticed some anomalies," Dr. Gonzalo notes. For instance, the recorders struggle to distinguish between different types of large gulls. They are also prone to misinterpreting contact calls, grouping them all together as the calls of the Lesser Whitethroat. The system has even picked up calls of species we would never see in Wiltshire, such as Puffins. 

To counter this, Dr Gonzalo sets the algorithm’s (BirdNET) confidence threshold to 80%, ensuring that only species identifications with at least 80% certainty are included. We also feed the algorithm the week of the year the recordings were collected to help it to account for seasonal variation in bird vocalisation. This, along with data from external databases such as Macaulay and Xeno-canto, BirdNet classifies the vocalisations into species. Monitoring device failures can also create gaps. "We can see lots of Tawny Owl vocalisations all the way up to mid-April, and then they abruptly stop altogether at every single site," says Dr. Gonzalo. "We have to assume the monitors stopped recognising them, and we will check the next data set to make tweaks to ensure they are picked up again."  

It’s still early days, but the data already shows which bird species are most prominent in different parts of the landscape. We are looking forward to a full year of data to compare against the new changes as the trees and other agroforestry elements become established. 
 
This winter, we will be using our baseline data to help to give us a clear starting point for measuring progress over time at Great Chalfield, setting realistic targets, and planning how we manage the site, all whilst ensuring these all align with our wider Wiltshire Wildlife Trust goals of securing nature’s recovery. 

You Can Help! The bioacoustics data is cross-checked by humans performing 'point counts,' where an observer counts the species they see or hear from a fixed location. You can contribute by recording bird calls and uploading them to xeno-canto, which helps to verify the recordings from our acoustic monitors. To do this is pretty straightforward - first, record the bird calls using a smartphone, being sure to note the species (you can identify the species using the Merlin app), make a note of the location, date, and file type, then upload the audio file to the xeno-canto website to share your data with a global community including our partner’s WSBRC. 
 
The acoustic monitoring devices were purchased thanks to an award from the North Wessex Downs National Landscape Partnership (https://www.northwessexdowns.org.uk).  

The analysis and work of the team is funded thanks to an award from the National Lottery Heritage Fund .