NATURE FOCUS SWALLOW
THERE are three similar looking species of bird that are both common and familiar UK summer visitors, swallows (also known as barn swallows), house martins and sand martins.
These birds all belong to the same bird family, Hirundinidae, and are often collectively referred to as “hirundines”.
Another summer visitor, the swift, looks superficially similar to hirundines, but swifts belong to a totally different family of birds, Apodidae, which also includes hummingbirds.
There are two sub-families within Hirundinidae, the first being Hirundininae, with 81 species worldwide, and Pseudochelidoninae, which contains just two species of river martins. Swallows have a glossy blue-back head and throat with a deep red chin patch and are buffy-white underneath. Swallows and martins are more often than not seen in flight and it is not always possible to get clear views but a swallow can be identified by its long, forked tail streamers.
Male swallows have longer streamers, with an average tail length of 108mm, compared to those of females at 90mm.
Female swallows tend to show a preference to mate with longer- tailed males, and there is strong evidence that males with longer streamers have a higher genetic quality and are seen by females as a more attractive mate.
It was thought at one time that longer tail streamers would result in additional drag during flight but it has now been shown that they actually increase manoeuvrability during flight.
Swallows can be found throughout the UK wherever there is suitable habitat. They feed on flying insects and favour open countryside with low vegetation such as farmland, meadows and pastures preferring those areas with water nearby. They tend to avoid heavily wooded areas and those with a high building density. Their feeding behaviour is a good weather indicator. In warm, dry weather, swallows fly high, seeking out insects which have been swept high into the air by the rising warm air currents. Conversely, during cold and unsettled weather, insects tend to seek shelter in grasses and trees and as such the swallows have to fly lower.
It is believed that the population of swallows has increased due to the development of rural communities and their use of the resultant man-made buildings for nesting.
Both sexes work together to build the nest, typically positioned on high ledges and beams. They construct the cup of the nest with mud pellets, which they collect in their beaks, lining it with grasses, feathers and other soft materials. It can take over 1,000 journeys back and forth from the nest site to complete nest building. Each summer, a pair will typically rear two broods and during a good breeding season, they will often raise a third.
Prior to migrating back to their wintering grounds, groups of swallows, sometimes thousands strong congregate in noisy groups and can sometimes be seen on telephone wires, often favouring reed with large numbers of birds swooping low over the reed beds to feed and diving into the beds to roost overnight. Reed beds provide an important food source enabling the birds to build up their energy stores prior to migrating.