Cetti's Warbler

This species can be found on the following statutory and conservation listings and schedules.

UK Birds of Conservation Concern	Green listed
Species of European Conservation Concern	Least Concern
IUCN Red List of Threatened Species (global)	Least Concern
Schedule 1 license required (to disturb)	Yes
Birds Directive Annex 1	No
Listed on the Annexes of	WCA(I,IV), Bern(III), Bonn(II)

Cetti's Warbler was first recorded in Britain as recently as 1961, as part of its range expansion across northwest Europe (Bonham & Robertson 1975). Colonisation, which began in Kent in 1972 or 1973, continued to be monitored annually by RBBP until 2016. Numbers and breeding range increased spectacularly during the first 12 years, with Norfolk and Dorset gradually overtaking Kent as the main host counties (Gibbons et al. 1993, Wotton et al. 1998). Populations in milder regions continued to grow, but overall the UK population fell by over a third between 1984 and 1986. In the absence of severe winters during 1986-2009, increase and range expansion continued. The first breeding records north of the Humber were made in 2006 (Holling & RBBP 2009).

Much constant-effort ringing takes place in prime Cetti's Warbler habitat; despite the comparative rarity of this species, therefore, CES population and productivity indices were already available by the early 2000s (Robinson et al. 2007a) and the species has also recently become sufficiently widespread to enable BBS trends to be produced. There has been an increase across Europe since 1989 (PECBMS: PECBMS 2020a>).

UK breeding population

+934% increase (1995–2022)

The explosive song of the Cetti's Warbler means that fieldworkers will have overlooked few breeding sites, although proving breeding is difficult. In 2007–11 Cetti’s Warblers occupied lowland wetlands in a broad but discontinuous band around the coast and are relatively common in certain river basins, such as the Thames, the Hampshire Avon and the Great Ouse. Other lowland areas of England and Wales are also occupied, but at lower density.

Since first breeding in the UK in 1973

Cetti's Warbler is recorded year-round, with distinct peaks in detection in spring when singing and in late autumn.

View a summary of recoveries in the Online Ringing Report.

Foreign locations of birds ringed or recovered in Britain & Ireland

View number ringed each year in the Online Ringing Report

Maximum Age from Ringing	9 years 3 months 28 days (set in 2008)
Typical Lifespan	2 years with breeding typically at 1 year
Adult Survival	0.499±0.039

Wing Length	Adults	59.6±3.8 | Range 54–65mm, N=446
	Juveniles	59.1±3.5 | Range 55-64mm, N=561
	Males	63.2±1.9 | Range 61–66mm, N=193
	Females	56.5±1.9 | Range 54–60mm, N=219

Body Weight	Adults	13.9±1.9 | Range 11.1–16.7g, N=421
	Juveniles	12.8±1.7 | Range 10.5–15.5g, N=542
	Males	15.6±1 | Range 14.4–17.1g, N=185
	Females	12.4±1.2 | Range 10.9–14.9g, N=203

Feather measurements and photos on featherbase

Ring size	A
Field Codes	2-letter: CW | 5-letter code: CETWA | Euring: 12200

For information in another language (where available) click on a linked name

Causes of change

It is likely that the population increases and range expansion of Cetti's Warbler were, at least partly, driven by climate change, with subsequent decreases in population caused by severe winter weather.

Further information on causes of change

Analysis of CES data shows that the rate of productivity has remained constant, and the initial steep increases are likely to have been aided by high productivity and overwinter survival, with population growth slowing as density-dependent effects started to occur, and severe weather also reduced numbers in some winters (Robinson et al. 2007a).

Information about conservation actions

This recent colonist is currently increasing its abundance and range in the UK, and hence no specific conservation actions are currently required. Actions to maintain and create wetland habitats for other species are also likely to benefit this species, the population of which "may be approaching its maximum size under current conditions" (Robinsonet al. 2007a). Reedbeds are particularly important for this species during the late summer and autumn (Araujo et al. 2016) and hence provision of this habitat at sites with wetland features may to help support and attract Cetti's Warblers.