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, may 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, much more recent decline. Both CBC/BBS and WBS show progressive moderate increases, perhaps linked to increasingly sensitive management of small and linear wetland sites and to the range expansion the species has achieved since the 1960s. 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	38	1967-2005	49	108	33	362
	25	1980-2005	64	90	29	227
	10	1995-2005	118	37	14	61
	5	2000-2005	117	9	-4	23
CBC/BBS England	38	1967-2005	47	80	16	236
	25	1980-2005	61	63	22	154
	10	1995-2005	113	31	11	56
	5	2000-2005	112	7	-5	22
WBS waterways	24	1981-2005	22	66	17	147
	10	1995-2005	26	34	0	98
	5	2000-2005	22	16	-5	51
CES adults	21	1984-2005	53	-31	-46	-10	>25
	10	1995-2005	61	-16	-28	-3
	5	2000-2005	56	-18	-28	-8
CES juveniles	21	1984-2005	54	-22	-37	7
	10	1995-2005	64	-5	-21	16
	5	2000-2005	57	-24	-36	-5
BBS UK	10	1995-2005	101	29	9	68
	5	2000-2005	113	13	3	28
BBS England	10	1995-2005	97	24	2	57
	5	2000-2005	107	10	-3	25

Productivity trends

Table of productivity changes for Reed Warbler

Variable	Period (yrs)	Years	Mean annual sample	Trend	Modelled in first year	Modelled in 2005	Change
Clutch size	37	1968-2005	111	None
Brood size	37	1968-2005	127	Linear increase	3.45 chicks	3.59 chicks	4.1%
Daily failure rate (eggs)	37	1968-2005	144	None
Daily failure rate (chicks)	37	1968-2005	109	Curvilinear	1.74% nests/day	0.53% nests/day	-69.5%
Laying date	37	1968-2005	159	Curvilinear	Jun 16	Jun 10	-6 days
Juvenile to Adult ratio (CES)	21	1984-2005	59	Smoothed trend	76 Index value	100 Index value	31%
Juvenile to Adult ratio (CES)	10	1995-2005	69	Smoothed trend	99 Index value	100 Index value	1%
Juvenile to Adult ratio (CES)	5	2000-2005	61	Smoothed trend	100 Index value	100 Index value	0%

Additional information


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This report should be cited as: Baillie, S.R., Marchant, J.H., Crick, H.Q.P., Noble, D.G., Balmer, D.E., Barimore, C., Coombes, R.H., Downie, I.S., Freeman, S.N., Joys, A.C., Leech, D.I., Raven, M.J., Robinson, R.A. & Thewlis, R.M. (2007) Breeding Birds in the Wider Countryside: their conservation status 2007. BTO Research Report No. 487. BTO, Thetford. (http://www.bto.org/birdtrends) Pages maintained by Susan Waghorn and Iain Downie: Last updated 3 January, 2008