Sylviidae – Sylviid Warblers & Allies

Sylviidae is a family of passerines that include the typical warblers Sylvia and the closely related genus Curruca, formerly included in Sylvia. They are found in Eurasia and Africa with the greatest diversity in the Mediterranean region.  Formerly they were part of an assemblage known as the Old-World warblers. The family was a wastebin taxon with over 400 species of bird in over 70 different genera. The family was poorly defined with many characteristics shared with other families.

Advances in classification, particularly helped with molecular data from DNA research, has led to the splitting out of several new families from within this group. Today the smaller family Sylviidae includes the typical warblers and a number of babblers formerly placed within the family Timaliidae. There is now evidence that these Sylvia ‘warblers’ are more closely related to babblers Timaliidae, and thus these birds are better referred to as just sylvids.

Sylviids are small to medium-sized passerines. The bill is generally thin and pointed with bristles at the base. Sylviids have a slender shape and an inconspicuous and mostly plain plumage. Blacks and greys predominate, sometimes with dashes of white or reds. The wings have ten primaries, which are rounded and short in non-migratory species.

Most species occur in Eurasia, and to a lesser extent in Africa.

The Common Whitethroat is typical of the family. It is widespread and common throughout much of Europe and western temperate Asia. It’s strongly migratory in winters in tropical Africa, Arabia and Pakistan. Like some of the family, it’s sexually dimorphic, although the sexes are quite similar, both brown above and buff below, with chestnut fringes to the secondary remiges. The adult male has a grey head and a white throat. The female lacks the grey head and her throat is somewhat duller.

Like most of the family, its song is distinctive, although often described as somewhat fast and scratchy, or with a scalding tone, and being hoarse and slightly nasal, especially in its calls rather than its song. Having said that, many of the family do have attractive and distinctive songs, and some, such as the Blackcap, pick up phrases from other birds around their breeding areas and incorporate them in their repertoire.

Garden Warbler Sylvia borin – ©Ashley Beolens

Eurasian Blackcap Sylvia atricapilla – ©Ashley Beolens

Like many of the family, it’s a bird of open country and cultivation, with bushes for nesting and vegetation to feed in or skulk in. Their nest is built in a low shrub, especially brambles, and three to seven eggs are laid. Like most warblers, it’s insectivorous, but will also eat berries and other soft fruit. In Europe, western and eastern populations of Common Whitethroats have contrasting moulting and pre-migratory fuelling strategies to capitalise on food supplies before departing to their breeding or non-breeding grounds.

In the United Kingdom, a number of species have begun to overwinter, especially with the change in weather patterns. Blackcaps, for example, and now to a lesser extent, both Common Whitethroat and Lesser Whitethroat do overwinter in the southern counties. They tend to survive the winter by eating more fruits, and some, like the Lesser Whitethroat, completely change their diet in autumn as they migrate, until arriving in the warmer areas they migrate to, where insects are again more common.

Feeding habits do, to an extent, dictate the limits to expansion of some species. For example, the Dartford Warbler stays all year in the more temperate areas of the United Kingdom. And as climate has begun to change, so has their area of occupation extended somewhat. The reason why they can survive, even though they are still insectivorous, is that they concentrate on arachnids rather than true insects and live amongst gorse and bramble, surviving on spiders and other arthropods.