Yorkshire, 18 February: house martins on their way?
These house martins were gathering mud to build their nests on 5 February, nearly two weeks ago. They were in the far south of Europe, in the village of El Rocío at the edge of the Doñana marshes.
I wondered if they had overwintered. Some field guides show a resident population of swallows in the area, but overwintering house martins would be unexpected. And it seemed unlikely - there were several hundred of them. In fact, based on previous visits I was not surprised to see them. Until recently, I was always skeptical about those overwintering swallows, too. Certainly, you can see swallows every day of the year in Doñana. But my hunch was always that there was a long overlap between late southbound migrants and early returners. After all, in Britain we usually get a few late November records, and even December birds are not unknown.
My guess is that the last southbound birds and the first northbound ones overlap around Christmas or New Year. This year, both swallow and house martin numbers started to build up in Doñana from mid-January. Whether climate change is tempting some to stay in southern Spain all year will be difficult to assess, but I may have to change my view about overlapping migrant swallows.
In this part of the UK, it will be difficult this year to work out what is going on with our birds. Although we are now seeing some vague signs of winter at last, in reality, last autumn gave way to spring-like conditions without winter seeing fit to intervene. I've been keeping an eye on BirdTrack, the BTO-hosted app where birdwatchers record their sightings. It is an accumulation of millions of individually insignificant pieces of data, that collectively is giving us new insights into the distribution and migrations of our birds.
I see that a handful of house martins have been hanging around in the west of Britain and in Ireland, with a smattering of December records, and a few in late January. The last was on 1 February, until this week, when the species has again been reported in Cornwall, on February 15. Why not take the optimistic view and imagine that this may be an early arrival, rather than a lingering bird from last year?
Laurence Rose is a conservationist, writer and composer. He has worked for the RSPB since 1983.