House martins are one of the heralds of spring here - swooping through the skies, catching midges. They may be here for only a few months but they live close amongst us - when the doors to the dye deck are open they swoop into the studio, circle and leave.
Wherever there is an overhanging roof or a handy corner, they will move in and begin constructing complex colonies of nests, often inconveniently above doorways. We have one group of nests above the bathroom window here, another above the back door.
Of course this wasn’t always the case, and up until the beginning of the C19th they were just known as martins. Most of them would make their nests in caves and on the underhang of cliffs, tucked in out of the wind. By 1900 though they had moved to easier territories, sticking their nests to the outside of houses, protected from predators and their name changed.
Each nest is intricately made up from about 1000 beak sized pellets, mainly mud which it then reinforced with strands of grass. If you are lucky you can watch them scoop up mud from wet ground, flying up to build another bit of the nest – at dusk you can see the lines of that day’s building, a darker line of wet mud. It takes 1-2 weeks to build a nest from scratch but only a couple of days to repair one from the previous year.
When we built a covered deck at the back of the house one year the house martins spent a couple of days circling their old nesting site and then decided to remodel rather than rebuild. They changed the position of the entrance - by filling the existing one in and cutting out a new one - to fit their new flight path to the side of the roof.
There are about 510,000 breeding pairs of house martins in the UK, each bird weighs only 20g and the average life expectancy is 2 years, though the oldest recorded was 14 years old.
The birds are socially monogamous – and will remain in the same breeding pairs for their life span. But they are prone to a bit of action on the side and a study in Scotland found that a third of nests had chicks from more than one father in them. While the male is off catching flies his rival will sneak into the nest.
Typically house martins will raise two broods in a year – the eggs hatch in 14-16 days and fledglings will leave the nest 22 days after hatching, returning to roost there for a couple of weeks with some still relying on parents for food.
One of the delights of this summer was watching the fledgling housemartins on the sweet pea trellis - with their parents chirping encouragement to try and get them to fly and catch their own food.
In late August and September house martins begin to gather on telephone wires, waiting to leave on their great migration to Sub Saharan Africa.
One of the things I find amazing is that at present we do not know exactly where they go once they leave the UK – there have been tracking projects to try and find out but so far none have been successful. Only one of the thousands of ringed birds has been found in Africa – in Nigeria. The rest seem to fly to and from the continent without being spotted by birdwatchers at all. I love that there are still mysteries like this in the world.
House martins are on the RSPB’s Amber warning list – numbers are decreasing. This may be due to the widespread use of insecticides and also to drought which makes both their migration and their nesting more difficult.
This is something that you can help with - they need wet mud to build their nests but they will also patch up already exisiting nesting sites. If you have heavy clay in your garden and it is dry them pour a bucket of water over it so that it becomes good nest building material. If you don’t have any suitable mud and you want to encourage them to nest on your house there are composite nests available which you can mount on your wall under the eaves.
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