We have to make do with the jerky two-note song of another migrant; the chiffchaff. Cuckoos may have fallen on lean times but chiffchaffs are doing well; they are nesting now in areas well north of their old European haunts.
These little olive-brown warblers frequent woodlands, mature wild hedges, and scrubby river margins. There are almost 60 lookalikes in the extended “leaf warbler” family, but only two are common in Ireland. Serious birdwatchers can tell chiffchaffs from willow warblers by sight in the field. However, to identify the bird reliably, I have to examine the wing formula of any “willow-chiff” caught in my garden mist-net. Each warbler has its own, unique, configuration of feathers with distinct emarginations, or notches, on them.
The chiffchaff’s “fingers”, the long wing-feathers, are shorter than those of willow warblers, a key to differences between the birds’ lifestyles. Although weighing no more than a €1 coin, these birds travel huge distances on migration. Some chiffchaffs cross the Sahara; Senegal is their holiday location of choice. Others remain on in Southern Europe and along the coastal fringes of North Africa. Willow warblers are more adventurous; they can travel as far as South Africa, the main wintering areas of Irish and British ones being the Ivory Coast and Ghana. Having longer wings helps them make their formidable journeys.
Referring to the chiffchaff as a summer visitor is misleading. “Partial migrant” might be a more accurate description; while most chiffchaffs leave, a few remain on here for the winter. Staying put is risky; chiffchaffs suffer during cold spells. Another wintering warbler, the blackcap, changes its diet to berries and visits bird-tables when the going gets tough. Chiffchaffs, however, eat only creepy-crawlies. They die of starvation and hypothermia during freeze-ups.
Telling warblers apart in the field is easy if you let the birds tell you who they are; chiffchaff and willow warbler songs are as different as sean nós is from Wagnerian opera. The willow warbler’s exquisite Schubertian cadences make it a Feis Ceoil winner but the chiffchaff’s rhythmic thumping, a binary sequence of ones and zeros, won’t win any prizes.
This little warbler was not given species status until comparatively recently; Gilbert White, of Natural History of Selbourne fame, is credited with discovering it. “I have now, past dispute, made out three distinct species of the willow-wrens which constantly and invariably use distinctive notes,” he wrote in 1789. His third “distinct species” was the wood warbler, a very scarce breeder in Ireland. Similar discoveries are still being made; in 2016, the Iberian chiffchaff of Spain and Portugal was deemed, officially, to be a distinct species.
The tendency to stay at home for the winter, avoiding the hazards of long-distance travel, isn’t a recent phenomenon; Richard Ussher and Robert Warren wrote that chiffchaffs were recorded in Ireland on 10 occasions between November and February during the 19th century. The winter bird survey of 1981 to 1983 found the birds mainly along the coast from Kerry to Wexford with concentrations in East Cork. My humble back garden has little to offer warblers, but one or two chiffchaffs visit it in winter. Some mainland European chiffchaffs, it seems, prefer to come to Ireland rather than fly south.
According to the 19th-century naturalist William Thompson, the chiffchaff nested in only seven Irish counties in the 1850s. By 1900, say Ussher and Warren, it was “an increasing species”. The bird reached Kerry in the 1950s. In 1970, only parts of Mayo and Roscommon had yet to be colonised. According to the 2007 to 2011 Bird Atlas, numbers increased here by 11% between 1998 and 2010. Loathe as I am to say it, global warming seems to be helping chiffchaffs.