The wren is almost certainly the most widely distributed types of bird in Britain, for whereas every other species is restricted by pretty much well-defined requirements for example woodland, moorland, open grassland, fens, sea-shore or reed-beds, the wren can exist successfully in a of these varied environments. It may be said to inhabit and exploit no one type of habitat, but instead the bottommost layer-the ground itself and some feet above it-of all of them.
This zone, at the base of covering vegetation, is full of insects, spiders along with other minute types of animal life, and among birds the wren has sole hunting-rights here. The dunnock shows some inclination to take advantage of similar zones, nevertheless its size limits its scope, which is barred from dense tangles by which the wren threads its way as quickly as a mouse.
It’s not only dark vegetation so it explores, and one do not need to go so far as a boulder-strewn shore in the Shetlands or Hebrides to possess proof of the wren’s fearless search for dark crannies and passages through rocks-in timber-yards, coal-stacks and builders’ yards one can observe spider-hunting wrens disappearing into one cranny and finally emerging from another, sometimes many yards away. The zone alongside the earth’s surface known does not necessarily need to be horizontal-near-vertical sea-cliffs, with crannies and overhanging tufts of vegetation, as well as the sea-weed itself at low tide, will still provide the requisite habitat.
With this very specialised mode of life the wren is admirably adapted-tiny body, however with comparatively stout legs and enormous probing beak; nevertheless its very smallness is the one chink in the armour. The wren, like the goldcrest, is dogged by the mathematical proven fact that surface area of the sphere increases in inverse ratio using its diameter-in other words, the smaller the bird the greater (proportionately) the surface that body-heat can be lost.
Thus the wren was one of the most severely reduced of common species in the prolonged hard winter of 1962-63. Inside a garden where annual records of birds passing through is kept, there have been 91 known individuals in 1961; in 1962, carrying out a winter by which there had been a brief period of intense cold, the number had dropped to 60; after the worst winter of, the number had fallen to six; but providing that the breeding nucleus remains, the wren soon recovers from such methods to the brink of extermination; it’s pleasant to record that the total for 1964 was 23.
The wren takes what steps it may to avoid lack of heat in the long winter nights; for rather than roosting in bushes in the open, since it will do in milder weather, it seeks a warm shelter like a nest of their own kind, a home martin’s nest, a nest-box, or it might squeeze its distance to the side of the rick. In extreme cold (as though aware of the mathematical law) parties of from five to ten may huddle together such snug shelters, thus effectively creating a larger spherical mass.