3 Partial migrants

Some Marsh Harriers undoubtedly do still head south, making them a species, like Chiffchaff, which can be described as a partial migrant. That’s to say, some members of a certain population do migrate, and others don’t (the Blackcaps we started with are slightly different, in that the movements involved two distinct populations).

In fact, a huge number of species are partial migrants, and in many cases the average birder doesn’t necessarily notice it happening. Take Blackbirds. In winter, some of our own breeding birds, and especially those in the colder north and east, move south and west. But they’re replaced by birds arriving from Scandinavia and the continent, so unless you look closely, you might not notice. These European Blackbirds are often black- billed first- winter males, which look the same as first- winter males fledged in the UK, so that’s not necessarily an indicator of provenance; but the sudden appearance of lots of black- billed Blackbirds is a strong indication that they are new arrivals.

Lapwings are another example. Some remain here all winter, generally moving to estuaries or wetlands (large flocks on farmland are mainly a thing of the past), but others move south to warmer climes. The list goes on. But the lesson to be learned is twofold. Firstly, don’t assume you’re seeing the same individual birds (those Blackbirds say), year- round. Secondly, all sorts of unexpected species are on the move all the time, so use the distribution maps in your field guide as just that. A guide.