Several people have said to me within the last few weeks that House Martin numbers appear to be much reduced and what has happened to them. Time will tell what the reality of that situation actually is this season. But running in parallel to all of this is the fact that we don't really know where, precisely, House Martins go in the winter months. Yes, we know they appear to go to Africa, but precisely where?
I certainly have seen House Martins in a variety of places around the Mediterranean in the late winter, but not in mainland Africa in numbers. Whilst large numbers have been ringed, few recoveries have been secured compared to Swallows. Whilst ringers in South Africa catch many Swallows at roost, no such terrestrial roosts of House Martins have been located, indeed sightings of birds are not that common. All in all an intriguing scenario in this day and age!! Occasional "wrecks" of House Martins have occurred in Zambia, where sightings of birds are not infrequent. It would seem that the birds can suffer from the the onset of cold and wet weather, gather in places to shelter and then be found dead in appreciable numbers.
To address this modern day mystery, the BTO are to attach several birds with small geolocators this summer in an attempt to discover what is involved. These devices are very small and weigh only about 1 gram. They measure daylight length and the location at the time can be determined from these results. Remarkable results are possible nowadays from the use of such miniature technology and the outcome of the research is already eagerly awaited!!