Bird ringing trainer Simon Lane and volunteer wildlife surveyor Rik McCoy report on the data gathered on Bere Marsh Farm in Dorset last summer. Simon and his ringing colleagues operate under licences issued by the British Trust for Ornithology (BTO). They carried out bird ringing on the farm 12 times between May and August 2022.

Their data has been submitted to the BTO’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.

The second year of the CES project at Bere Marsh Farm followed a disappointing year for breeding birds across the country in 2021. British Trust for Ornithology (BTO) analysis of the national results has shown that, for several species, breeding productivity was lower in 2021 than for any other year since the CES scheme started in the mid-1980s. The most likely explanation for this low productivity is the very cold and wet weather conditions that prevailed during the breeding season. Consequently, the population of most species was lower than normal at the start of the 2022 breeding season.

After an unsettled early spring, the weather in 2022 was generally good for most of the CES period, with a prolonged spell of high temperatures and low rainfall during mid-summer. Consequently, all twelve of the standard CES visits to Bere Marsh Farm were successfully completed. Two additional visits were also made in September and October to monitor the late migration period, as encouraged by the BTO.

The favourable conditions were beneficial for most species, although blackbirds can struggle to find worms for their young when the ground is too hard. Very hot conditions can also reduce the number of flowers, and the availability of seeds may have been a problem for some later breeding attempts.

The ringing site has a very diverse range of habitats including woodland, ponds, pasture, scrub and the River Stour. As such, it should be suitable for a wide range of species, and it is therefore not surprising that almost all the species monitored by the CES scheme are present.

Five new species recorded

The total number of individual birds recorded in 2022 was markedly higher than in 2021. This was due, in part, to the lack of one visit in the first year but that does not account for the 37 per cent increase. The number of species also increased from nineteen to twenty-four, with woodpigeon, sedge warbler, whitethroat, marsh tit, coal tit and chaffinch all being recorded for the first time in 2022*.

The number of almost all species increased, although blue tit and reed warbler are notable exceptions. The higher number of reed warblers in 2021 may have resulted from several birds being ringed during the first two visits, as these birds may have still been on migration due to the challenging weather conditions during the spring of that year.

In 2022 there were a consistently high number of birds recorded for all twelve visits. In years of poor breeding success, the catches tend to drop off towards the end of the season, as was seen in 2021. The breeding success was significantly better in 2022, with more than sixty percent juveniles compared with less than forty percent in the previous year. This is a crude measure of breeding success as it is based on all species and excludes a few individuals (mostly long tailed tits) that could not be aged reliably.

Breeding success for robin and blackbird

A more detailed analysis of breeding success is gained by studying the percentage of juveniles for the six most abundant species – blackbird, black cap, chiffchaff, dunnock, robin and wren. This percentage increased significantly for five of the species but remained essentially constant for wren.

After a disastrous year in 2021, the percentage of juvenile blackbirds more than trebled to thirty nine percent in 2022. While this is still lower than would be expected in a good year, it is higher than seen at other sites in 2022 and it is likely that the availability of muddy areas at Bere Marsh Farm during the very dry summer would have helped this species. The data also indicates that robins bred exceptionally well, with over ninety percent of the individuals recorded being juveniles.

We also study relative species abundance – a measure of how common or rare a species is relative to other species in a defined location – to enable clearer comparison between years. On Bere Marsh Farm, the relative abundance of the various types of species did not change significantly in 2022, compared with the previous year.

The relative abundances of finches and buntings were essentially unchanged between the years but were surprisingly low. It is difficult to explain why this should be the case, as the habitat appears to be ideal for chaffinch, bullfinch and reed bunting to breed successfully. The relative abundance of tits was lower in 2022 but these species tend to move around in large family groups after fledging and catching one or two of these groups can have a disproportionate effect on the data.

More than five hundred birds were ringed at Bere Marsh Farm during 2022. These include birds caught during visits in the early spring and at the two additional visits in the autumn. The species ringed outside the CES season are essentially the same as those ringed during the summer, with only one additional species – greenfinch.

The main purpose of ringing in general, and the CES scheme in particular, is to monitor change. Although it is already possible to make comparisons between the two years of the project, the true value of constant effort ringing is only realised after many years, when long term demographic changes can be reliably identified.

Acknowledgements

We would like to thank The Countryside Regeneration Trust for allowing us to have access to this very productive site and both Wildlife Monitor Andy Fale and Bere Marsh Farm Manager Elaine Spencer-White for supporting the project. We 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.

 

*Editor’s note: all of these species have been recorded on the farm previously by walking surveys carried out by CRT wildlife monitoring staff and volunteers, but this was the first time they have flown into the bird ringing team’s nets and been ringed.

Andy Fale, the CRT’s Wildlife Monitor for Dorset, said: “The ringing data complements the surveying data very well. The surveyors record birds from the whole farm giving a good indication of the species present, while the ringing data looks in detail at the birds in a small area, which can give information on migration and breeding success. The insight from both methods helps inform our management of the farm and its habitats. The effort put in by the surveyors and ringers is tremendous and is very much appreciated.”

All birds ringed at Bere Marsh Farm (including non-CES visits)

Species	2021	2022
Woodpigeon	0	1
Kingfisher	1	0
Greater Spotted Woodpecker	1	5
Wren	33	41
Dunnock	18	29
Robin	19	28
Blackbird	22	27
Song Thrush	5	5
Sedge Warbler	0	1
Reed Warbler	15	12
Whitethroat	0	1
Garden Warbler	2	2
Blackcap	38	66
Chiffchaff	24	73
Willow Warbler	2	3
Goldcrest	9	12
Long Tailed Tit	29	67
Marsh Tit	0	2
Coal Tit	1	5
Blue Tit	28	63
Great Tit	23	42
Treecreeper	7	3
Jay	1	0
Chaffinch	0	4
Greenfinch	5	1
Bullfinch	8	8
Reed Bunting	0	2
TOTAL	291	503

Breeding success for six abundant species

The ratio of adults to juveniles for six of the most abundant species. This gives an indication of the breeding success for these species.