A team of licensed volunteers carried out bird ringing on Bere Marsh Farm in Dorset 12 times between May and August 2023. 

Not only does the information they gather contribute to the understanding of how songbirds are faring nationally, it is also helping our team to plan how to improve the habitats on Bere Marsh Farm in an effort to support breeding birds. 

Their data has been submitted to the British Trust for Ornithology’s Constant Effort Sites (CES) scheme. This national standardised ringing programme enables the monitoring of trends in the abundance, productivity and adult survival rates for 24 species of common songbird. All the bird ringing is done under license from the BTO and within current avian influenza guidance.

Bird ringing trainer Simon Lane reports on the data gathered on Bere Marsh Farm in Dorset this summer:

The third year of the CES project at Bere Marsh Farm was completed successfully with all twelve visits accomplished. After a relatively mild winter, the weather was very wet during the early spring and the breeding season was consequently delayed for many species. The weather was so unsettled on the Iberian Peninsula and Northwest Africa that many summer migrants arrived several weeks later than normal and it is likely that a significant number may have perished before reaching the UK.  

The weather conditions were generally favourable during the four months of the CES period, although heavy rain during May resulted in very high water levels in the River Stour. This is likely to have adversely affected early breeding attempts by reed warblers and possibly some other species. 

The excessive temperatures prevalent in 2022 were not repeated in 2023 and the vegetation thrived throughout the summer, with grass still growing vigorously at the end of August.

 Disappointing year for breeding success

The start of the CES project at Bere Marsh Farm, in 2021, coincided with the worst breeding season, across the UK, since the CES scheme started in the mid-1980s. As expected, the number of birds increased in 2022 and it was disappointing that the number present in 2023 was lower than in the first year, as shown in the table below. 

Initial indications from the BTO suggest that abundance has been very low at many sites in 2023, but a quantitative analysis of the national picture will not be available until early 2024. 

The data suggests that the low overall abundance of many species is a combination of low productivity and lack of breeding adults, as the percentage of juvenile birds is relatively high. This contrasts with 2021, when the adult abundance was reasonably high, but the percentage of juveniles was extremely low (less than 50 per cent). 

Summer migrants breed successfully

No chiffchaffs were ringed until the fourth visit in early June. Indeed, the blackcaps and reed warblers ringed during the first three visits may well have still been moving north.

Although the summer migrants returned late and in low numbers, those that did manage to breed at the site, did so successfully. Indeed, the percentage of juveniles was higher, for all three warbler species, than in either of the previous years. 

However, it can be seen that reed warblers have struggled to breed at the site in all three years, which may be a combination of regular flooding and the relatively small patches of Phragmites reed that are available for nesting.

Difficult year for resident species

The relative abundance of juvenile robins and dunnocks was higher than in 2021, but lower than last year, for both species. Wrens and blackbirds had their worst year to date. This is particularly surprising for blackbirds as the ground remained soft all summer and the availability of worms should not have been a problem, whereas productivity actually increased in the extremely hot and dry conditions last year.

The relative abundance of warbler species (predominantly blackcaps and chiffchaffs) was higher than in either of the previous years, but this was at the expense of resident species and tits. However, a young marsh tit and a young coal tit were ringed, which suggests that both species bred successfully at the site.

There was a slight increase in the relative abundance of finches, but this remains very low, at less than five percent.  

Insights into bird movements

A reed warbler ringed at Loire-Atlantique in France on the 26th of August last year was caught at Bere Marsh Farm on the 7th of May this year. This bird was not recorded at the site again, so was probably still moving north in May.

A greenfinch ringed at Bere Marsh Farm on the 15th of December 2021 was found dead in Iwerne Minster in Dorset on the 16th of April this year, having hit glass. 

Acknowledgements 

I would like to thank The Countryside Regeneration Trust for allowing us to have access to this very productive site and Farm Manager Elaine Spencer-White and her colleagues for supporting the project. 

I would also like to thank the other members of the ringing group who helped with the fieldwork and contributed to the cost of the rings.

“Thank you to Simon and the team who carry out bird ringing on Bere Marsh Farm. Without this kind of data, we would not have evidence on the scale of change to bird populations either at particular locations or nationally. 
“Combined with the data our wildlife monitors gather through walking surveys, this information helps us to make informed decisions about how to manage CRT land for the benefit of wildlife. For example, we already have hedgerow and grassland management plans in place on Bere Marsh Farm to boost biodiversity in these habitats. We are now looking into how we can manage the scrub with rotational cutting to provide the varied levels needed by different species of breeding birds. 
“This data also enables those of us involved in conservation policy to persuade politicians to have in place measures to protect and restore nature.”

Sue Everett, CRT Chair

Total number of individual birds caught each year at CES visits

The table below includes re-traps from previous years (first re-captures only). No non-CES visits were carried out this year.

 

Breeding success for seven abundant species

The graph below shows the ratio of adults to juveniles for seven of the most abundant species. This gives an indication of the breeding success for these species.

 

Published: 13th November 2023
Photo credits: TOP: Marsh tit by Susann Mielke from Pixabay. RIGHT: Eurasian reed warbler by Nick Dobbs. LEFT: Common chiffchaff by Nick Dobbs.

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