Species update
House Martin research is vital to better understand declining breeding numbers – and you can help, explains Kate Risely
The BTO want your help in monitoring House Martin nest boxes – find out why
ONE OF THE pleasures of spring is watching the House Martins busily gathering mud from the lane near my front door – in dry spells I keep a muddy puddle topped up with water for this purpose! I don’t know where the colony is, but they aren’t thought to travel more than a few hundred metres to gather nesting materials, so they can’t be far away. Each cup nest requires a thousand mud pellets to build, meaning a thousand round trips to a suitable muddy area. It’s perhaps not surprising that they take short cuts when they can, often choosing to renovate old nests, or stealing mud from their neighbours’ constructions! Originally, of course, they would have nested on rock outcrops, but across much of Europe they have fully shifted to nesting on buildings, and, here in the UK, there are only a few colonies in ‘natural’ sites. They tend to stay faithful to the colony where they were hatched, though females are more likely than males to move to new sites. However, they don’t seem to stay faithful to the same mate, often pairing up with a new partner each year, and even switching partners during the breeding season, especially if their first nesting attempt was unsuccessful. They will have two or three broods during the season, with juveniles from the first brood often helping to feed their younger siblings from later broods. During the breeding season adults and full-grown fledglings will roost overnight in the nests or nearby, but some birds may sleep on the wing high above the colony. Ringers have reported birds descending from high above in the pre-dawn, which, when caught coming in to the colony, were freezing cold to touch. This may give some clues as to their wintering habits; while they are known to winter across a wide swathe of Africa, they are not often seen in lowland areas, and it’s thought they spend much of their time in very remote highlands or foraging at high altitudes. It’s been speculated that their unique feathery feet might be an adaptation to the cold! Their wintering areas and habits remain among the unsolved mysteries of bird migration studies; more than 400,000 House Martins have been ringed in the UK, and while this has given us valuable information on survival and return rates, it has not helped pinpoint their wintering grounds, as only one British-ringed House Martin has ever been recovered south of the Sahara. Tracking devices are as yet too large to use safely on House Martins. The BTO’S bird monitoring programmes indicate that we have lost around 70% of our House Martins since the 1970s, and this trend has continued to be overall downwards in recent years. Many reasons have been suggested for these declines, including the effects of rainfall on mud for nesting, and declining insect numbers on the breeding grounds, resulting in a lack of food for chicks, as well as problems on migration. In order to better understand House Martin breeding numbers, and the reasons for changes, the BTO is currently running a large-scale House Martin Survey. This started with random-site nest counts in 2015 to quantify numbers of breeding pairs, followed by nest observations in 2016 to look at breeding ecology and habitat preferences. Anyone can observe a House Martin colony this year to help us learn more about what factors affect House Martin numbers, and help us pinpoint the stage in the life cycle that is driving these declines.
The BTO’S bird monitoring programmes indicate that we have lost around 70% of our House Martins since the 1970s, and this trend is continuing