The chiffchaff is one of several warbler species that migrate to us from Africa in spring for the breeding season and then head back south again in early autumn. I always reckoned to hear my first chiffchaff on, or about, the 15th March each year and, interestingly, the weekly chart shows a surge in tweets in week 14, around the 15th March! They do start arriving a little earlier than that it seems as reports start to pick up a couple of weeks before week 14. Being an early arriver compared to other warbler species the chiffchaff does get quite a bit of attention from observers when they see their first of the year, it shows that migration is under way and spring, in theory at least, is just around the corner.
The weekly chart makes interesting viewing in my opinion as it shows a sudden decline in reports from mid-May through until early August. There are two reasons for this I would imagine. Firstly, the chiffchaff is a common nesting species in Dorset and so there is little interest in reporting a sighting once first arrivals have been noted. The second reason could be that they become less visible once the leaves come on the trees and their song stops when territories have been established and the work of feeding young starts. From early August until early October reports pick up again as the autumn exodus begins.
A further look at the weekly chart also shows a small number of reports from November and December, a break in January and then a few reports from February. How come a summer visitor is seen here out of season? When I started 'birding' back in the 1970s this was something of an unsolved puzzle; why would some birds not follow their comrades south in autumn and decide to stay on here? It was suggested that an increase in bird feeding might be leading to a change in the species behaviour and that it could lead to substantially more deciding to stay and overwinter. That might seem a bit naive now as I think it is pretty well established that birds seen here in winter are from northern Europe who migrate here rather than go on south to Africa. The lack of records in January might indicate that the late autumn birds arriving here may then move on into France and Spain when the going gets tough here in January?
The distribution map shows just how widespread this species is in Dorset and how catholic it is in choice of habitat. They seem to be happy pretty much anywhere there is a tree to perch in and sing from. There are a substantial number of records from Portland where their migration is easily monitored.
If the chiffchaff is on your 'hit list' to see then the best time is in early spring when there are few leaves on the trees and where you can first locate them by their distinctive 'song' (after which they are named of course). As I said, you can see them almost anywhere.