My study window looks out over a 10-acre meadow with a small hill on the far side. Under the grass on the hill there’s esker sand and gravel laid down in the last Ice Age. Back in the days when the main forms of transport round here were powered by horses and donkeys people had to be more locally self-sufficient, particularly for heavy items like sand and gravel, and a small quarry was opened up on the west side of the hill.
The quarry was abandoned a long time ago and sand and gravel now comes in lorries from far afield. At least, it was abandoned by human beings but a colony of sand martins took over. They bored their nesting tunnels, some of which can be over a metre long, into the vertical face of the pit, choosing the strata with bands of easy-to-excavate sand rather than the coarser gravel. And, during the day, they fly out over the 10-acre meadow catching insects on the wing.
The sand martin has two Irish relatives, the house martin and the swallow (swifts are not related) and it is the smallest of the three. It also has a shallower fork to its tail and is a bit stubbier in appearance. This gives it a different flight pattern, more abrupt than a swallow with less of the flowing loops and arabesques.
Despite this I still enjoy watching them through the window. Some days they fly very close to the ground, on other days they will be 30 or more metres up in the air. The weather seems to be the controlling factor. When humidity or wind is high the flying insects must stay low but on a fine, dry day they will be higher.
Then, a few days ago I looked out and they were gone. Sand martins tend to leave on migration about a week to 10 days before swallows or house martins. They also arrive a bit before them in the spring. They have a very large world range and because of this they are not regarded as vulnerable or endangered despite the fact that numbers are declining. Data from the US, where they call them bank swallows, also shows that their spring migration is about 10 days earlier than it was 100 years ago.
This is presumably due to global warming. I haven’t found any research that duplicates this finding for European sand martins.
The birds from the field outside my window probably headed east and crossed the Irish Sea to Pembrokeshire. They then headed south-east and crossed the channel from eastern England. Then they will head south- west, taking a coastal route through France and Iberia. Some will head down the west coast of Africa, others will cross the Sahara.
Their eventual winter destination is a swathe of western and central Africa from the coast of Senegal to wetlands in Mali’s Niger valley and over to Lake Chad.
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