Red-throated Diver Gavia stellata

Regular, scarcely common winter visitor and migrant, rare to vagrant June to Sept, RI(w)

 

Peaking in Oct, up to 20000 pass along the East Coast from populations in Scotland, Norway and Iceland with some dispersing later along the South Coast to winter and pass en route to the Continent. This, the commonest and smallest of the divers is usually found here offshore, but occasionally appears within the estuary, on most winter days and regularly through spring. Owing to its sporadic distribution along the South Coast, the number of regular birds here are of some significance. Bird-days per annum vary considerably and ranges of just 35 to 178 have occurred within the 1990s and since 1987 a total of 1139 bird-days (59.9% of all diver records) have occurred.

 

Early autumn arrivals include singles 20 Aug 1989, 27 Aug 1985 and 28 Aug 1979; Sept and Oct birds are quite scarce occurring in 11 and 15 of the past 20 years (1980 - 99). Most birds normally return from early-Nov and an influx from mid-Nov to early-Dec typically sees a max of three or four although exceptional counts include ten 24 Nov 1988 and nine 14 Nov 1981. A brief lull is followed by a mid winter period late-Dec to early-Feb which generally records the largest numbers including 12 of the 26 two-fig counts including 38 on 3 Jan 1956 and 22 on 9 Feb 1980. Most wintering birds depart by late-Jan to mid-Feb.

 

The spring migration period is variable and unpredictable, some years are drawn out with low counts, others with a late surge and depending on the year, migration can end in late-Mar, or even late-May. 12 two-fig counts lie between late-Feb and mid-May with max counts of 24 on 11th & 31 on 14 Mar 1984, 15 on 23 Apr 1967 & 3 May 1981. Records stop abruptly after late-May and there have been nine June records since 1950 and four of the five July records have been since 1985, the most unusual being an over-summering individual 29 June-30 July 1995.

 

Table 2: monthly total bird-days and no of dates 1987-99*

Month

J

F

M

A

M

J

J

A

S

O

N

D

B-dys

259

100

127

114

82

9

2

1

20

58

197

170

No dts

85

41

50

51

53

8

2

1

18

30

93

74

Table 3: annual total bird-days, no of dates, max and date 1974 - 1999*

Year

1974

1975

1976

1977

1978

1979

1980

1981

1982

B-dys

-

-

-

40

42

96

100

130

-

Max

7

5

6

5

5

11

22

15

7

Date

lt yr

e yr

2/5

20/3

3/12

12/5, 24/11

9/2

3/5

4/4

 

Year

1983

1984

1985

1986

1987

1988

1989

1990

B-dys

-

-

-

-

71

74

68

54

No dts

-

-

-

-

35

39

41

28

Max

6

31

9

3

6

10

5

10

Date

13/4

14/3

2&13/3

23/11

5/1,24/4

24/11

29/1

30/12

 

Year

1991

1992

1993

1994

1995

1996

1997

1998

1999

B-dys

71

86

35

123

70

66

175

147

99

No dts

34

35

16

36

38

34

72

59

39

Max

12

13

10

15

8

7

12

9

10

Date

6/1

12/1

16/1

23/1

19/11

23/2

16/3

10/12

20/12

         1st date only for July 1995 & Sept 1999 birds