Monday 31 January 2022

A baseline established – Ringing in a Chesham Bois garden (2021)

 

The year 2021 began with yet another lockdown and, as is so often the case, the sequel was miserable. The first lockdown in 2020 was novel, interesting and characterised by a warm, dry and sunny spring. January in 2021 was cold, dark and oppressive and we approached the national lockdown with a sense of weariness and resignation. Fortunately, I was able to find some cause for cheer – I could find the time to survey birds in my garden and complete a full year of study. Having gained my C permit in April 2020 I was unable to start ringing in my garden until part way through that year. This time, I could aim to complete a full year of study to provide a baseline for monitoring my garden birds over time.

Part of that study would involve ongoing participation in the new Garden CES (Constant Effort Site) project which was introduced by the BTO to provide an outlet for qualified ringers with time on their hands and limited access to traditional sites in 2020. I had elected to contribute to the Garden CES in its first year and planned to continue my involvement in 2021. Whilst I was very glad indeed that the lockdown had been lifted by May when the CES began, this did restrict my ringing activities as I could only keep the nets up in the garden until the necessitated commute to work. In 2020, I was able to keep the nets open until 11am which was not an option in 2021. This was a real shame because I learnt towards the end of the year that the data collated in 2021 couldn’t be used in a comparative study by the BTO as the timeframes for ringing between the years were not the same – I guess the clue was in the name – ‘Constant’ Effort Sites. For that reason, the CES data collected in 2021 also represents a baseline for comparison with future years – at least for the purpose of BTO analysis. However, it’s worth noting that the number of birds caught in the latter stages of the 2020 ringing sessions tended to fall away quite quickly, so the data is broadly comparable for the purposes of this report.

The total number of birds caught in the 2021 CES period (167 = 13.92 per session) was almost the same as 2020 (168 = 14 per session) and the species count was similar with 20 species caught in 2020 and 23 species in 2021. However, the assemblage of species was slightly different in this second CES, with 7 new entrants in 2021 (Blackcap, Garden Warbler, Goldcrest, Magpie, Marsh Tit, Song Thrush and Stock Dove). Four species captured in 2020 did not feature in the 2021 CES data set (Chiffchaff, Great Spotted Woodpecker, Jay and Whitethroat) although all, bar Whitethroat, were caught at other times in the calendar year of 2021.      

There is no way of drawing statistically significant comparisons between years when looking at the abundance of each species, but there are some interesting figures to consider. In particular, the number of Goldfinches (22; 13 in 2020) and Greenfinches (7; 3 in 2020) captured in 2021 was considerably higher and the number of Long-tailed tits (3; 11 in 2020) and wrens (3; 7 in 2020) was lower. I will return to blue tit numbers later.

Table 1: Garden CES 2021 – Ringing Records (figures in green higher than 2020; figures in red are lower than 2020)

Species / Visit 

1

2

3

4

5

6

7

8

9

10

11

12

Total

Average

Blackbird

 

1

 

 

1

3

1

1

 

 

 

 

7

0.58

Blackcap

 

 

 

 

 

 

 

1

2

1

1

 

5

0.42

Blue Tit

 

 

1

2

7

4

6

3

2

4

9

8

46

3.83

Bullfinch

 

 

1

 

 

 

 

1

 

 

 

 

2

0.17

Chaffinch

1

2

 

 

 

 

 

 

 

 

 

 

3

0.25

Chiffchaff

 

 

 

 

 

 

 

 

 

 

 

 

0

0.00

Coal Tit

 

 

 

 

 

 

 

 

 

 

1

 

1

0.08

Dunnock

1

 

 

 

1

1

3

4

2

2

 

 

14

1.17

Garden Warbler

 

 

 

 

 

 

 

 

 

1

1

 

2

0.17

Goldcrest

 

 

 

 

 

 

 

 

 

1

 

 

1

0.08

Goldfinch

1

1

1

1

8

1

4

3

 

 

2

 

22

1.83

GS Woodpecker

 

 

 

 

 

 

 

 

 

 

 

 

0

0.00

Great Tit

2

1

1

 

 

1

 

2

 

 

4

2

13

1.08

Greenfinch

 

1

 

 

2

 

1

2

 

1

 

 

7

0.58

Jackdaw

 

1

 

1

 

 

 

 

1

 

 

 

3

0.25

Jay

 

 

 

 

 

 

 

 

 

 

 

 

0

0.00

Long-tailed Tit

1

 

 

1

 

 

 

 

 

 

1

 

3

0.25

Magpie

 

1

 

 

1

 

 

 

 

 

 

 

2

0.17

Marsh Tit

 

 

 

 

 

 

 

 

 

 

1

 

1

0.08

Nuthatch

 

 

 

1

 

 

 

 

 

 

 

 

1

0.08

Robin

2

 

3

 

1

 

2

1

1

1

2

 

13

1.08

Song Thrush

3

 

 

 

 

 

 

 

 

 

1

 

4

0.33

Starling

1

3

2

1

1

 

 

 

 

 

1

1

10

0.83

Stock Dove

 

1

 

 

 

 

 

 

 

 

 

 

1

0.08

Whitethroat

 

 

 

 

 

 

 

 

 

 

 

 

0

0.00

Woodpigeon

 

 

 

1

 

 

 

1

 

 

1

 

3

0.25

Wren

 

1

 

 

 

 

 

1

 

1

 

 

3

0.25

Total

12

13

9

8

22

10

17

20

8

12

25

11

167

13.92

Species number

8

10

6

7

8

5

6

11

5

8

12

3

23

7.42

 

 

In addition to the CES sessions, there were many more occasions during the year when I was able to ring in the garden – in total there were 54 separate sessions in comparison with 48 in 2020. However, these were spread across the full year, whereas ringing in 2020 was limited to the months of May to December. This makes comparisons tricky once more, but there are some interesting figures in table 2 which may provide some evidence of changes in abundance between years.

 

Table 2: Ringing Totals for 2020 and 2021

 

2020

2021

Species

Ringed

Retrapped

Total

Ringed

Retrapped

Total

Blackbird

16

6

22

18

12

30

Blackcap

6

0

6

24

1

25

Blue Tit

118

30

148

97

48

145

Bullfinch

3

3

6

3

0

3

Chaffinch

10

0

10

1

3

4

Chiffchaff

1

0

1

3

0

3

Coal Tit

11

4

15

7

7

14

Dunnock

21

26

47

18

36

54

Firecrest

1

0

1

2

0

2

Garden Warbler

0

0

0

2

0

2

Goldcrest

8

2

10

16

5

21

Goldfinch

35

1

36

55

8

63

Great Spotted Woodpecker

4

0

4

1

0

1

Great Tit

47

10

57

35

10

45

Green Woodpecker

1

0

1

0

0

0

Greenfinch

9

0

9

17

2

19

Jackdaw

6

0

6

4

1

5

Jay

1

0

1

1

0

1

Lesser Redpoll

1

0

1

1

0

1

Long-tailed Tit

25

20

45

21

3

24

Magpie

0

0

0

4

0

4

Marsh Tit

0

0

0

1

0

1

Nuthatch

2

1

3

5

4

9

Redwing

6

0

6

13

0

13

Robin

21

20

41

22

31

53

Siskin

2

0

2

8

0

8

Song Thrush

0

0

0

8

0

8

Starling

32

1

33

24

3

27

Stock Dove

0

0

0

1

0

1

Whitethroat

2

0

2

0

0

0

Woodpigeon

2

1

3

4

1

5

Wren

10

5

15

11

6

17

Total

401

130

531

427

181

608

Per session

8.4

2.7

11.1

7.9

3.4

11.3

 

Whilst recognising the limitations of any comparisons between years, it is interesting to note that many more Greenfinches, Goldfinches, Blackcaps, Goldcrests and Song Thrushes were caught in 2021, whilst the number of Chaffinches and Tits was lower. The Blue Tit data is particularly interesting given earlier speculation about the impact of the cold spring on productivity. It has been suggested that the cold weather delayed the emergence of oak leaves and their favoured caterpillar prey, resulting in greater rates of nest failure and low recruitment to the population of blue tits nationally. However, my localised data shows that whilst the population of Blue Tits may have decreased slightly (2.7 per session compared to 3.1 per session in 2020), the number of juvenile birds in 2021 was considerably higher – see table 3. Given that the span of the year in which juvenile birds were present was sampled equally in both years, this comparison seems valid. The number of Blue Tits caught in the 2021 CES period was actually higher overall (46; 36 in 2020), but this is largely down to the number of juveniles. It was striking that no Blue Tit adults were caught in the first 2 CES sessions at all.

Table 3: Blue Tit adult : juvenile ratios in 2020 and 2021

 

2020

2021

Adult totals

88

40

Juvenile totals

60

105

Adult : Juvenile

1 : 0.7

1 : 2.6

 

If anything, this data supports the notion that Blue Tit productivity was actually higher locally in 2021, with many more juvenile birds present than 2020. Conversely, adult survival may have been lower in 2021 – perhaps the challenge of feeding nestlings with limited food supplies had more of an impact on exhausted adults? It will be interesting to see the BTO data on Blue Tits to see if my figures align with any national trends.

In time, I sincerely hope that my data will provide a useful contribution when aggregated within the national data sets analysed by BTO. At the moment, it is early days for ringing in Chesham Bois, so I can’t really analyse trends yet, but that time will come. Hopefully it will reveal recoveries in bird numbers and variety through time from this baseline, which is surely lower than it would have been in preceding decades. Nevertheless, my garden ringing activity has provided me with some interesting insights into my small local patch already. I would never have predicted such a variety of species – indeed, before ringing, I had never seen Firecrests, Garden Warblers or Whitethroats in my garden – a true revelation. I wouldn’t have been able to speculate about Blue Tit survival and productivity and I wouldn’t have had any appreciation of the total number of birds visiting my patch. There are some regular repeat visitors - one poor robin has been caught 26 times (!) – but there are many more individuals that pass through, as I have caught 43 robins in total across two years.

The ringing projects for 2022 are now underway and I can’t wait to find out what they will throw up – any forecasts for new ringing records or winners and losers in 2022 – answers on a postcard to Chesham Bois please.

By Ian Cooksey

Stock Dove - First ringing record for the garden

A male Starling in full breeding plumage

A juvenile Marsh Tit - a first ringing record for the garden

Juvenile Garden Warbler - another first ringing record for the garden

A male Chaffinch - a very rare sight in 2021