The dawn chorus is a particular feature of early spring in the Suffolk countryside.
Over the last few days the chorus of resident blackbirds, song thrushes and great tits has been joined by the first of the summer migrants to reach our shores. One of the most obvious of these new songsters is the chiffchaff, whose simple two-syllable song gives this rather plain looking warbler its name.
The chiffchaff is a short-distance migrant, largely wintering in southern Europe and North Africa. However, over recent years we have seen increasing numbers of chiffchaffs overwintering further north, including birds which now remain in Britain rather than venture south. It is thought that this change in behaviour is a response to a changing global climate – the milder winter conditions enabling these small insectivorous birds to survive. Most of those wintering in Britain are to be found in southern and south-western Britain, favouring waterside habitats, where temperatures may be a few degrees warmer and densities of active insects that much higher.
Many people assume that small birds, like warblers, nest in shrubs and trees, some distance off the ground, but most make their nests surprisingly close to ground level. While the willow warbler nests on the ground, the chiffchaff usually makes its nests just a few inches off the ground, typically in a low bramble with other material pushing up through it. The chiffchaff nest is made from grass, dead leaves and moss, woven into a ball-like dome. The nesting chamber is lined with feathers and it is into this that the birds will lay their clutch of five or six eggs. Suffolk’s chiffchaffs are already busy building their nests, with many male birds having been on territory for a fortnight or more. Although many of our small migrants only have time to rear a single brood of young, chiffchaffs make two nesting attempts, perhaps reflecting their relatively early arrival each spring.
While the two-note song will reveal the presence of a breeding chiffchaff territory, it is the off-nest note of the female that those participating in the BTO’s Nest Record Scheme (www.bto.org/nrs) use to locate the well-hidden nest itself. The female calls to her mate whenever she is away from the nest; by finding a calling female it is possible to watch her back to the nest. Once she enters the nest the calling will cease. By marking the position of where the female went quiet, BTO nest recorders can return a bit later to gently ‘tap’ the female off the nest before recording the nest contents. A nest recorder will make four or five visits to a chiffchaff nest over the course of the breeding season, building up a picture of its success or otherwise and making a valuable contribution to our understanding of how our small summer migrants are faring.