The complications of migration

Walking around Corby in the last 10 days or so, the sweet song of the Blackcap has been much in evidence from gardens, parks and woodlands, along with the very similar song of the closely-related Garden Warbler.

The latter's song is just that bit more mellow and gentle, but even many experienced birdwatchers can struggle to tell them apart.

But there's one very major difference between the two species. Garden Warblers spend the winter in Africa, and arrive back in the UK in April. Blackcaps, on the other hand, often only migrate as far as Spain and Portugal during the winter months (birds ringed near Corby have been recovered in both countries), then return in March and April.

But more and more people are seeing Blackcaps during the winter, often visiting garden feeders. So, are these birds that have given up on migration?

Well, no. In fact, the evidence is that our breeding Blackcaps still head south for the winter, but are replaced in some areas by birds from Central Europe, especially Germany, who find our mild winters preferable to the much colder climate there. When spring arrives, they return to the Continent.

It's another example of how complicated migration is. Birds are always on the move, even around us is the woods and parks of Corby, without us necessarily noticing.

And if you want to see a Blackcap, look for a small, slightly plump, grey-brown bird with a black cap (male) or rufous brown cap (female). The song starts with a lot of chattering, before opening out into a pleasant, fluting warble.

On the move

Bird migration is a strange phenomenon. This year, Sand Martins appeared before the end of February, and the first Swallows started popping up just after mid-March, but here we are, a week into April, and there's still relatively few Wheatears around the country, despite them being a species that usually spearheads the arrival of summer visitors.

There can be all sorts of reasons, with weather being the most obvious. Birds arriving from the Continent need southerly winds to make the crossing of the English Channel. Before that, those that winter in Africa also need friendly winds to make the crossing of the Mediterranean and the Sahara before that.

There's every chance that the winds this weekend will turn around favourably, and that we'll see a consequent influx of migrant birds. Chiffchaffs and Blackcaps are already singing their hearts out around Corby, but expect them to be joined by other warblers – Garden, Sedge and even Reed warblers, and perhaps Whitethroat and Lesser Whitethroat too.

Throughout this week, though, Northamptonshire generally has seen plenty of bird movements. Small, straggly flocks of Redwings and Fieldfares have been making their way east and north, heading back to their homes in Scandinavia and beyond.

And in Northampton itself, Waxwings are still feeding on berry-laden bushes and trees, fattening themselves up one last time before they make the journey back to northern Russia.

It's a reminder that migration is a constant, year-round process, in which the seasons blur into each other. Only at the end of this month will we be able to say that spring has truly arrived, but by then, incredibly, the start of autumn migration will only be weeks away, as Arctic-breeding waders start to head south again.