The sight of sand martins soaring overhead is one of the many joys of summer at Blashford Lakes nature reserve. Every year they arrive in their hundreds to make use of custom built nesting banks overlooking Ibsley Water.
Sandbanks occur naturally on eroding riverbanks and cliffs, and provide expansive areas in which sand martins can build their nests and rear their young. However, suitable nesting sites are becoming increasingly difficult to find. Riverbanks are often reinforced with man-made materials to reduce flood risk, leaving little space for sand martins to make their burrows. Quarries are also popular nesting spots, but these are often subject to large scale extraction techniques - this means that the sand faces are not left in place for long enough to allow for nesting.
With this in mind, we set out to help our local population of sand martins at one of our flagship nature reserves. We built specially designed nesting banks at Blashford Lakes, and the results have been spectacular.
In 2008, Reserves Officer Bob Chapman and his faithful group of volunteers set about building a haven for sand martins. Using a steep section of shore overlooking Ibsley water and materials donated by Hanson Concrete Plant, they built a wall on the edge of the lake. 183 carefully sized holes were inserted into the wall, and behind each one they placed a metre-long plastic pipe filled with sand. Each pipe was filled by hand and fixed in place, and the wall was rendered to give it a more natural look. The end result was an outstanding nesting site fit for a colony.
Just a few months after the bank was completed sand martins started visiting the holes, and pretty soon about 40 pairs were nesting. By summer the following year, numbers had more than doubled, and this year about 150 pairs are nesting. Every summer the view from Goosander Hide is alive with the dainty fluttering of these industrious little birds.
Sand martins are fairly common summer visitors to the UK and one of the earliest to arrive, the first turning up in early March or even late February. These gregarious birds nest in large colonies which may contain hundreds of pairs, and they dig deep burrows in steep, sandy cliffs. The tunnels they bore can be up to a metre in length, and in a chamber at the end of the burrow, an average of four or five eggs are laid in a cosy nest of grass, feathers and leaves.
The juvenile birds from the first brood will set off south in late June, leaving the parents free to rear more young. The last birds will make their way back to warmer climes in October when flying insects (their primary food source) start to dwindle in numbers. Most are thought to spend the winter in the Sahel, the zone south of the Sahara where the hot, humid climate offers a plentiful supply of invertebrates.