Skylark population trends in Oxfordshire and Berkshire

 Declines in abundance, increased distribution, and support for

protected areas

article written by Kieran Storer

Skylark, Alauda arvensis, is an iconic British countryside species, foraging and nesting in grassland and semi-natural agricultural settings. Land management changes since the 1990s however, have resulted in sweeping skylark declines. Intensive agriculture (e.g. year-round crop cover and herbicide use) reduces over-winter food sources and nesting opportunity/quality, resulting in low chick survivorship. Additionally, reduction in natural grassland and meadowland are thought to have contributed to this precipitous decline in skylark. As a result, skylark is on the RSPB red list and is classified as Priority Actions Needed by Natural England, and there are ongoing efforts to support the species through protected areas (e.g. Wildlife trust sites), habitat restoration, and agri-environmental schemes which free up patches of agricultural land from intensive management.

Using records from the Thames Valley Environmental Records Centre (TVERC) on skylark sightings, abundance, and location in Oxfordshire and Berkshire, I investigated 1) local skylark abundance trends since the 1960s 2) patch occupancy changes over time 3) how skylark group size has changed over time and 4) what locations skylarks are being sighted at most frequently to understand what areas are consistently supporting skylarks. The overall aim of this project was to understand local skylark trends in abundance and location to estimate the efficacy of support schemes and protected areas and identify areas where more information is needed.

Utilizing statistics and graphing software I analyzed data on the year, location, and number of skylarks sighted from records provided by TVERC to investigate questions of abundance and occupancy. I graphed the abundance of skylarks sighted over time, the sighting effort over time, and the ratio of the two to correct for abundance changes that may result from changes in sighting effort.

I then used the data from the TVERC to map which areas of Oxfordshire and Berkshire skylarks have been sighted, highlighted sightings which overlap with protected areas, and used the software to isolate sighting locations decade (1960s-2010s). I then investigated sighting locations in the last 10 years as it related to group size, which I categorized as low (1-10 skylarks in a sighting), medium (10-50 skylarks in a sighting), and high (50+ skylarks in a sighting) to see whether sites are supporting larger groups, smaller groups, or both. Finally, I used a pie chart to establish the locations of skylark groups of small and large size to identify trends in location frequency.

Initial results showed that yearly abundance of skylarks sighted has been increasing in tandem with increased sighting effort, with an overall decline in the mean number of skylarks per sighting event since the mid 1990s. Interestingly, 2020 has seen an increase in skylarks per sighting event, perhaps due to increased effort coupled with the season of sightings (spring and early summer) which may skew the average number per sighting higher than typical yearly averages.

From the maps of Oxfordshire and Berkshire I found that skylarks have been occupying more patches since 1960 despite abundance declines, indicative of a positive long-term trend in patch occupancy. By categorizing skylark groups into small, medium, and large I was able to identify that in the majority of patches, small groups of skylarks (1-10 individuals) were sighted. This suggests that most occupied patches are supporting smaller groups of skylarks, an expected result from implementation of agri-environmental schemes which provide small fragments of suitable habitat and therefore smaller population sizes. Supporting this trend, location frequency data shows that ~5x more sites have sightings of small groups of skylarks (1-10 individuals) than large groups (50+ individuals). Larger groups made up a small minority of sightings (53 out of 2600+ total sightings) and are only usually seen once at a site, suggesting that larger groups may be formed temporarily or are transient, and not landscape fixtures. The majority of small group sightings and large group sighting overlapped with protected areas, suggesting 1) protected areas are more consistently supporting skylarks 2) sighting effort in protected areas is elevated (resulting in more records), or both. In any case, protected areas are where you would expect to see more skylarks, and this data positively supports that assumption.

While evidence supports declining skylark populations in Oxfordshire and Berkshire, skylarks are being sighted in more areas. This suggests that the available suitable habitat is not supporting high populations of skylarks, but that they are becoming more evenly distributed across the landscape. A priority for skylark conservation should be increasing the abundance of skylarks in patches that they occupy regularly, whether by improving patch connectivity, patch quality, or reducing disturbance so that higher regional populations can be sustained. This work does not in any way exclude other factors causing skylark decline, and it is important to continue to identify and disentangle population trends from factors such as accessibility for sighting efforts, disturbance factors, and the ecological impacts of setting aside discrete small patches. These results preliminarily support the work that has been done to provide and improve habitat patches, such as the agri-environmental schemes, restoration projects, and new protections which have been put in place. Further uptake of such measures may help the Oxfordshire-Berkshire skylark population to stabilize, support larger populations, and continue to increase patch occupancy.

I would like to thank the Thames Valley Environmental Records Centre for providing me with the data and this valuable opportunity to evaluate Alauda arvensis in Oxfordshire and Berkshire.