BTO - Breeding Birds of the Wider Countryside: Reed Warbler

REED WARBLER
Acrocephalus scirpaceus

• Population
changes

• Productivity
trends

• Additional
information

Conservation listings

Europe: no SPEC category (concentrated in Europe, conservation status favourable)
UK: green

Long-term trend

UK: uncertain

UK population size

60,800–122,000 pairs in 2000 (1988–91 Atlas estimate updated using CBC/BBS trend: BiE04, APEP06)

Status summary

This species has an unusually clumped distribution, with very high breeding concentrations in Phragmites reedbeds, where numbers are very hard to census. Because of this, CES, which has many sites in reedbeds, should perhaps be a better measure of population change than either CBC/BBS or WBS, where the species is encountered mainly at low density or in linear habitats. CES shows a decline from 1983 until the early 1990s, followed by a partial recovery, and another more recent decline. Both CBC/BBS and WBS show progressive moderate increases, however, perhaps linked to increasingly sensitive management of small and linear wetland sites. Population increase, as indicated by the census work, accords with the remarkable range expansion the species has achieved since the 1960s. West Wales, northwest and northeast England were colonised, as was the east coast of Ireland, between 1968–72 and 1988–91 (Gibbons et al. 1993), and the species probably now breeds sporadically as far north as the Tay reedbeds (Robertson 2003). Breeding performance as measured by brood size and failure rates has improved slightly, and a small improvement is apparent in CES productivity. The trend towards earlier laying can be partly explained by recent climate change (Crick & Sparks 1999).

Population changes

Table of population changes for Reed Warbler

Source	Period (yrs)	Years	Plots (n)	Change (%)	Lower limit	Upper limit	Alert
CBC/BBS UK	39	1967-2006	52	106	39	263
	25	1981-2006	70	84	31	201
	10	1996-2006	125	27	7	51
	5	2001-2006	125	7	-6	20
CBC/BBS England	39	1967-2006	50	80	22	202
	25	1981-2006	67	60	20	150
	10	1996-2006	120	24	7	42
	5	2001-2006	119	7	-3	20
WBS waterways	25	1981-2006	22	55	5	151
	10	1996-2006	26	23	-11	83
	5	2001-2006	22	12	-9	45
CES adults	22	1984-2006	52	-33	-46	-10	>25
	10	1996-2006	60	-26	-36	-13	>25
	5	2001-2006	52	-22	-31	-11
CES juveniles	22	1984-2006	54	-28	-45	-4	>25
	10	1996-2006	62	-23	-34	-9
	5	2001-2006	55	-32	-42	-19	>25
BBS UK	11	1995-2006	107	28	9	50
	10	1996-2006	111	23	7	43
	5	2001-2006	125	9	0	19
BBS England	11	1995-2006	103	25	6	50
	10	1996-2006	106	20	5	42
	5	2001-2006	119	9	-1	20

Productivity trends

Table of productivity changes for Reed Warbler

Variable	Period (yrs)	Years	Mean annual sample	Trend	Modelled in first year	Modelled in 2006	Change
Clutch size	38	1968-2006	110	None
Brood size	38	1968-2006	127	Linear increase	3.45 chicks	3.58 chicks	4%
Daily failure rate (eggs)	38	1968-2006	144	None
Daily failure rate (chicks)	38	1968-2006	110	Curvilinear	1.74% nests/day	0.5% nests/day	-71.3%
Laying date	38	1968-2006	159	Curvilinear	Jun 16	Jun 10	-6 days
Juvenile to Adult ratio (CES)	22	1984-2006	59	Smoothed trend	81 Index value	100 Index value	24%
Juvenile to Adult ratio (CES)	10	1996-2006	67	Smoothed trend	108 Index value	100 Index value	-7%
Juvenile to Adult ratio (CES)	5	2001-2006	58	Smoothed trend	109 Index value	100 Index value	-8%

Additional information


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This report should be cited as: Baillie, S.R., Marchant, J.H., Leech, D.I., Joys, A.C., Noble, D.G., Barimore, C., Grantham, M.J., Risely, K. & Robinson, R.A. (2009). Breeding Birds in the Wider Countryside: their conservation status 2008. BTO Research Report No. 516. BTO, Thetford. (http://www.bto.org/birdtrends) Pages maintained by Iain Downie, Mandy T Andrews and Laura Smith: Last updated 18.02.2009