Swallows in Cumbria

(April 25, 2019)


We used to call them “Swallows” but, as there are a dozen or so swallow species in their African wintering grounds, the “politically correct” name for our species is now “Barn Swallow”. As the names imply, our Barn Swallows are more rural than House Martins, preferring to nest on a ledge in an outbuilding or barn with more open cattle pastures around for feeding.

In an interesting piece of evolutionary adaptation some Swallows have established a colony of 10 – 15 nests underneath the bridge that carries the A590 Dalton Bypass over Thwaite Flat……perhaps they should be called Box-girder Swallows not Barn Swallows!!! The box-girders of the bridge afford ample ledges and shelter. However, every time a vehicle hurtles across the bridge there is a loud thud as it passes over the expansion plates. Neither the noise nor the vibration seems to deter the birds, although lesser mortals like us would get a thumping headache and their homes would probably collapse if they lived with this twentyfour-seven.

In fact the birds arrive back in late April/early May after spending the winter on the southern tip of Africa with 300 million or so other Barn Swallows from all over Europe. Even with the traffic, Thwaite Flat must seem like a peaceful haven compared to the noise experienced at a night-time roost there!

In another piece of adaptation to man made structures, Swallows characteristically rest on telegraph and electricity wires, which provide an unimpeded access that suits their swooping flight. Even the young seem to have this habit built in, as they often line up on wires after fledging, waiting to be fed (see photo below):

These are tough little beasts anyway. At five months old they begin an incredible 12000 mile round trip that sees them travel across the English Channel, the Pyrenees, the Sahara Desert, Equatorial Africa and down the east coast of South Africa …then back again two months later. Each night a roost site has to be found and an incredible variety of predators and weather conditions must be overcome. During the four days it can take to cross the Sahara an ascent to 3 miles may be needed in order to spot the next oasis fifty miles away. Fewer than 20% of first year birds make it back again but, of those that do, many find their way back to the same nest site each year (for up to ten years).

The House Martin is also a species that has readily adapted to man-made structures although there are a few places in the county where they still build nests in their ancestral habitat of cliffs and crags. More usually they build their mud homes under the eaves of buildings, with favourable sites acquiring a growing number of nests as the years progress. Very dry weather in Spring can cause serious problems as they must collect an enormous amount of mud of the right consistency. This is the only time when House Martins can be observed close up and relatively still -they are so intent on the job in hand (or beak) that they are relatively approachable. Now their gorgeous plumage can be seen in detail – note the tell-tale white rump seen in flight but also the uniquely white-feathered legs (please get in touch with me if you know of any theory for the evolutionary benefit of this adaptation!). It is also possible to distinguish male and female at this time, as males have slightly longer tail feathers.

While Swallows and House Martins are widespread in the county, the Sand Martin is much more localised and has suffered quite serious declines in the county in recent years. It requires suitable soft banks near water for it’s nest tunnel and is largely confined to the Eden valley (where the river banks are very suitable), with small numbers on cliffs north of Ravenglass and on a few sand cliffs in Furness. It will readily take to artificial nest tunnels, such as drainage pipes laid in concrete walls as on the River Kent. It is an opportunist species, adapting as the environment changes and numbers can fluctaute markedly from one year to the next – this site (left) has held good numbers in some years but only one or two pairs in others. Equally I have seen single pairs nesting in a sand dune blow out and on a small bank on an airfield!

The nature of their nests mean that they can be susceptible to predators like Stoats, Weasels and Hedgehogs.