Sevenoaks Constant Effort Site

This is the fourth year of constant effort ringing at Sevenoaks which takes place at a site set up in an area of scrub to the south of the East Lake
.  One visit is made in every ten-day period from May until the end of August.  As can be seen from the table below eleven of the twelve periods were covered by a visit representing about 132 hours of field work. Additional visits were made during the period but these catches are not included in the CES analysis.

          CES Visits During 2003

Visit No.

Date

Capture Total

1

3 May

26 (22)

2

11 May

21 (22)

3

25 May

18 (19)

4

8 June

20 (36)

5

21 June

19 (37)

6

23 June

No visit (63)

7

9 July

31 (82)

8

20 July

13 (41)

9

27 July

18 (34)

10

3 August

15 (22)

11

17 August

17 (36)

12

24 August

12 (29)

The 2002 capture totals are shown in brackets

The capture table below shows the number of adult and juvenile birds of each species captured in 2003 and compares these with those for 2002.  A major factor that limits the value of a straight comparison is the omission of visit 6 this year which is normally the most productive session. However, some degree of interpretation is possible without the need to apply mitigating statistics. Some species are caught in such small numbers that attempts to draw conclusions from year-on-year comparison would be statistically unsound. Nonetheless, the more commonly caught species do show some interesting trends.

Similar numbers of adult birds were caught this year but the number of juvenile birds caught shows a marked decline.  Nowhere is this more marked than in the case of Blue Tits and Great Tits (see nest box item).  It seems that the damp and cold climatic conditions of early spring had an effect on many breeding passerines, which was most marked in single brood species, but which probably affected the early broods of multiple brooders where the catches of juveniles was also depressed.  Wrens and Dunnocks seem to have bucked this trend but Robins and Long-tailed Tits have suffered.  The cherry crop failed to attract Starlings this year but Blackbirds turned up in good numbers to enjoy the feast.  One very welcome but unexpected feature was the return of the Bullfinch, catches of which outnumbered Blue Tits for some time.  Nationally the Bullfinch is still a declining species but this study indicates a good breeding season and a local revival in this part of Sevenoaks. 

Turning to the migrant passerines, Willow Warblers, which were relatively common in 2000 with twenty-six birds caught were almost non-existent, with only a single juvenile bird caught. Blackcaps have continued to thrive and have had a good breeding season and Garden Warbler numbers are holding up but the two early Lesser Whitethroats failed to stay and breed and the Whitethroat continues to avoid the area even though the habitat seems favourable.

CES Captures for 2003 compared with 2002

Species
2002
2003
Adults
Juveniles
Total
Adults
Juveniles
Total
Kingfisher
.
1
1
.
.
.
Green Woodpecker
3
1
4
4
.
4
Great Spotted Woodpecker
.
3
3
1
.
1
Wren
6
8
14
5
13
18
Dunnock
14
16
30
18
12
30
Robin
8
29
37
8
11
19
Blackbird
22
24
46
10
20
30
Song Thrush
11
7
18
9
2
11
Sedge Warbler
.
1
1
.
.
.
Reed Warbler
.
1
1
.
.
.
Lesser Whitethroat
1
1
2
2
.
2
Garden Warbler
5
1
6
7
1
8
Blackcap
13
7
20
14
14
28
Chiffchaff
6
17
23
3
3
6
Willow Warbler
.
1
1
.
1
1
Long-tailed Tit
1
10
11
.
.
.
Blue Tit
4
22
26
2
4
6
Great Tit
3
33
36
4
13
17
Treecreeper
.
6
6
4
1
5
Coal Tit
.
.
.
.
1
1
Jay
1
3
4
.
1
1
Starling
1
11
12
.
.
.
House Sparrow
1
.
1
1
.
1
Chaffinch
1
5
6
2
.
2
Greenfinch
5
2
7
1
4
5
Bullfinch
2
1
3
6
8
14
Totals
108
211
319
111
109
210