Grasshopper Warbler is “the most artful creature, skulking in the thickest part of a bush”, according to Gilbert White in 1768. It belongs to the genus Locustella, which includes some of the most secretive birds in the Western Palearctic. These warblers walk, run, creep and hop in almost mouse-like fashion through dense vegetation, and are often found close to the ground.
They can be seen in coastal scrub on migration, but for breeding will use both dry and wet habitats. Scrubby grassland with bushes, heathland, open woodland and newly replanted areas of forestry are popular, but probably the largest numbers are found in reedbeds and wetland edges.
This species’ breeding distribution is patchy across Europe, and the European subspecies seems to spend the winter in the western half of West Africa. Other subspecies occur eastwards to Mongolia, wintering in India. The few British ringed birds that have been recaptured were found wintering in Senegal and The Gambia.
Observations in Senegal, where large numbers of wintering birds have been seen, indicate that most have left the country by early February. Information from bird observatories in Britain shows that the earliest arrivals are on the south coast in late March, but the main influx takes place later, during the second half of April and early May. The majority of birds turn up on the western side of Britain, with relatively few seen at east coast observatories.
Autumn migration begins as early as July and there are three peaks, corresponding to three broods, in late July, late August and late September. The birds' route takes them down through France and Portugal, where there appear to be stop-over sites. They continue south through Morocco, where they are commonly recorded as prey of Eleonora’s Falcons, and down to West Africa.
Grasshopper Warblers migrate at night, and on occasion large numbers have been killed at lighthouses. On 29 August 1968, a total of 111 Grasshopper Warblers was found among almost 600 dead warblers on Bardsey Island, Gwynedd.
A Grasshopper Warbler sings with its bill wide open, turning its head from side to side. This gives a ventriloquial effect; it is almost impossible to place exactly where the song is coming from, and its intensity alters constantly. Singing birds are especially vocal around dusk and dawn.
The trilling song is made up of double notes, which are repeated at a rate of 25 per second. The trills can last for five minutes and may be given throughout the night, with the smallest of pauses between trills. Males sing most when they first arrive on territory. When paired up the frequency of song declines, but singing continues until July with short, sporadic bursts later in the summer.
Grasshopper Warbler has declined in numbers in Britain, particularly from the 1960s to the 1980s, even though it appears to be increasing in continental Europe. The British decline may be linked to problems with breeding habitat, and winter survival may also vary, as favoured wintering areas may flourish one year and be dried out the next. It is now a Red List species following a population decline of more than 50 per cent over the last 25 years.
How to find
The easiest way to find a Grasshopper Warbler is by ear. They are secretive and skulking most of the time and only really make themselves known by singing. They may sing at any time during the day and night, especially when newly arrived, but the main song period starts up in the evening before sunset, perhaps as early as 8 pm, and continues until dawn. So a late evening visit to a likely site may bring rewards, as might a dawn vigil.
Actually seeing the bird is quite a challenge. Once you’ve found a singing male, look for it among small bushes, perhaps within a reedbed. They will use the same song perch regularly and are often well hidden during the day. Listen carefully and try to locate the centre of the song area, as this is where the bird is likely to be. Watch patiently, as they will occasionally move along their perch and give their position away.
Where to find
- Dorset: Radipole Lake RSPB (SY 672805)
- Kent: Stodmarsh NNR (TR 221609)
- Oxfordshire: Otmoor RSPB (SP 563138)
- Cambridgeshire: Wicken Fen (TL 564706)
- Suffolk: Minsmere RSPB (TM 473672)
- Norfolk: Hickling Broad (TG 428221)
- Leicestershire: Rutland Water (SK 877072)
- Nottinghamshire: Clumber Park (SK 626753)
- Lancashire: Leighton Moss RSPB (SD 478750)
- Yorkshire: Potteric Carr (SE 589007) and Blacktoft Sands RSPB (SE 843232)
- Bridgend: Kenfig (SS 801811)
- Swansea: Oxwich (SS 500865)
- Carmarthenshire: Tregaron Bog (SN 685632)
- Ceredigion: Ynys-hir RSPB (SN 682961)
- Anglesey: Newborough Warren (SH 404648)
- Dumfries and Galloway: Wood of Cree RSPB (NX 383715)
- Clyde: Barons Haugh RSPB (NS 750550)
- Strathspey: Insh Marshes RSPB (NH 800020)
- Co Fermanagh: Lower Lough Erne Islands RSPB (HO 85605)