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 11^th & 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 n^o 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
N^o dts	85	41	50	51	53	8	2	1	18	30	93	74

Table 3: annual total bird-days, n^o 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
N^o 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
N^o 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

· 1^st date only for July 1995 & Sept 1999 birds