Northern Ireland's Priority Species

Locustella naevia – grasshopper warbler

 
Locustella naevia

Locustella naevia (Boddaert)
Family: Sylviidae

The grasshopper warbler is a widely distributed but fairly scarce summer visitor, arriving in May and leaving in August. The best indication of its presence on the breeding grounds is its continuous, whirring song which sounds like a fishing line being reeled in. The song is most often heard at dawn and dusk. Grasshopper warblers are found in marshy grassland with abundant scrub or rushes, young forestry plantations on bogs and clear-felled areas. Their olive-brown plumage and skulking habits make them difficult to see. They appear to have undergone a rapid decline in Britain and Ireland in the 1970s and 1980s, possibly as a result of habitat loss, though the populations have shown little net change in more recent years.

In brief

  • Scarce but widely distributed in suitable habitat throughout Northern Ireland

  • Associated with a variety of habitats, including marshy grassland with scrub, rushes and bushes, young forestry plantations, cutover bog and clear-felled areas

  • A summer visitor from May to August

  • It is a Red-listed species on UK Birds of Conservation Concern (BOCC) list, and Amber listed in Ireland

  • Declines are likely to have occurred due to habitat loss

  • More often heard than seen.

Species description
It is a medium-sized songbird similar in size to the more conspicuous and much commoner sedge warbler. The adult has a streaked brown back, whitish-grey underparts, which are unstreaked except on the undertail. The rounded wings and tail are noticeable in flight. The sexes are identical, as with most warblers, though the young birds, seen in the autumn, are more yellow below. It is a skulking species which is usually difficult to see, though sometimes it can be visible on a low perch, otherwise it tends to creep through grass and low foliage. The song, which gives the bird its name, is a remarkably continuous but monotonous insect-like reeling, recalling a fishing line being reeled in, often given at dawn and dusk. Like most warblers, it is insectivorous.

Life cycle
The breeding season begins May or early June and two broods can be raised in a season. The nest is built by both parents, and is usually placed in a hollow in thick vegetation, with a good ground cover of brambles or grass. The nest site is often near to bushes and small trees which provide suitable song posts. Clutches consist of typically six pale-coloured eggs, which are densely speckled brown or purple, and are incubated for about two weeks, after which the chicks are fed by both parents, leaving the nest at about 15 days. Insects form the main diet. They begin to leave their breeding grounds in August, the Irish and British populations probably wintering in north-west Africa.

Similar species
Confusion is possible with the sedge warbler, but the distinctive plumage and voice differences make them easy to separate. Sedge warblers have a distinctive long, pale line over the eye, contrasting with a dark crown as well as a lively and varied song, sometimes taking short flights as it sings. The ‘reeling’ song can be confused with that of the much rarer nightjar but the nightjar song is less monotonous and varies in pitch and tone as well as being delivered in much shorter, louder bursts.

How to see this species
Best listened for in damp, overgrown habitats, with small bushes, between late April and July when they sing from low perches. They can be heard mostly at dawn and dusk, but often sing through the night when the song is far carrying.

Current status
They were recorded as relatively widespread and common in Ireland during the 1970s, but apparently suffered severe declines of 35 to 40 per cent in both Britain and Ireland by the time of the New Breeding Atlas, 1988-1993. Further data from the Common Bird Census in Britain, though based on a dwindling sample size, indicated declines of over 59 per cent from 1972–1996. For this reason, they are Red listed on Birds of Conservation Concern in the UK, though in the last ten years, there has been little net change in the UK population. They are Amber listed in Birds of Conservation Concern in Ireland and are not a species of conservation concern in Europe, where they are widespread. They are protected under the Wildlife (Northern Ireland) Order 1985 and EC Birds Directive.

Why is this species a priority in Northern Ireland?

  • Red listed on UK Birds of Conservation Concern (BOCC) list.

It is Amber listed on Ireland BOCC list.

Threats/Causes of decline
In Northern Ireland, the greatest cause of decline has probably been drainage, scrub removal and the loss of inter-drumlin hollows, all of which have led to loss of potential suitable breeding habitat. Maturing forestry plantations are also a possible cause, but problems in their wintering areas have not been ruled out. Many long-distance migrants, including grasshopper warbler, increased in numbers by more than 5 per cent between 2003 and 2004, but these inter-annual changes do not necessarily reflect the underlying population trends. Overall declines in some of these species have been recorded across Europe in the last ten years. It could be that conditions in Africa influence the trends, both between two successive breeding seasons and over the longer term. Further research is being undertaken to examine more closely whether factors on the wintering grounds are responsible, at least in part, for these species' declines.

Conservation of this species

Current action

  • The population in Northern Ireland is monitored under the Breeding Bird Survey, a joint BTO/EHS/RSPB initiative, which has monitored common breeding bird populations since 1994

  • Agri-environment schemes include a range of measures which are likely to be of benefit to a range of species, including grasshopper warbler. These include measures for protection of species-rich grassland, wetlands, farm scrub and land adjacent to lakes

  • Many of the most important wetland sites in Northern Ireland have been designated as ASSIs and this usually includes a buffer zone of wetland fringe vegetation, an important factor in protecting grasshopper warbler habitat

  • Implementation of the Northern Ireland Habitat Action Plan for Fens.

Proposed objectives/actions

  • Maintain the population and range of grasshopper warbler in Northern Ireland by ensuring no further decline in numbers below the current BBS levels

  • In the long term, see a sustained recovery in numbers so that the BBS index increases.

What you can do

  • Consider becoming a volunteer for the Breeding Bird Survey and help to monitor the population in Northern Ireland

  • Ensure your local MLA knows that you support measures for the protection of biodiversity in Northern Ireland

  • If you own or manage farmland, consider participating in an agri-environment scheme.

Further information

Links
For information on agri-environment schemes open to farmers and landowners visit the Countryside Management Branch web site.

For information on the Breeding Bird Survey, visit the BTO web site.

More information on grasshopper warbler from RSPB.

Northern Ireland Habitat Action Plans

Literature
Eaton, M.A., Noble, D.G., Hearn, R.D., Grice, P.V, Gregory, R.D., Wotton, S., Ratcliffe, N., Hilton, G.M., Rehfisch, M.M., Crick, H.Q.P. and Hughes, J. (2005). The state of the UK’s birds 2004. BTO, RSPB, WWT, CCW, EN, EHS and SNH, Sandy, Bedfordshire.

Gibbons, D.W., Reid, J.B. and Chapman, R.A. (1993). The New Atlas of Breeding Birds in Britain and Ireland: 1988-1991. Poyser, London.

Gibbons, D.W., Avery, M.I., Baillie, S.R., Gregory, R.D., Kirby, J., Porter, R.F., Tucker, G.M. and Williams, G. (1996). Bird species of conservation concern in the United Kingdom, Channel Islands and Isle of Man: revising the Red Data List. RSPB Conservation Review 10: 7–18.

Newton, S., Donaghy, A., Allen, D. and Gibbons, D. (1999). Birds of Conservation Concern in Ireland. Irish Birds 6(3): 333-344.

Sharrock, J.T.R. (1976). The Atlas of Breeding Birds in Britain and Ireland. Berkhamsted: T. and A.D. Poyser.

Text written by:
Allen & Mellon Environmental Ltd.