THERE is a noticeable change in the behaviour of the birds in my garden.
Some have given up using the feeders. Others just pay brief and hurried visits. All this is because the nesting season has started, placing heavy demands on the time and energy of garden birds.
Nests are built by some insects, spiders, mammals, even a few fish species, but none approaches the complexity and variety of the nests birds build. The only other species that devotes so much energy and ingenuity to a structure in which to rear its young is Homo sapiens.
Among most bird species, the female chooses the nest site and dominates the building. Female dunnocks do all the nest building and the most extreme example is the red-necked phalarope, which formerly nested in Co Mayo. The female phalarope builds the nest but as soon as she has laid her eggs she disappears, leaving the male to do all the incubation and to rear the chicks.
In many other bird species the female initiates the nest building but then the males join in, though often the female is in charge. There are exceptions. Males are the dominant nest builders among house sparrows, blue tits and wrens.
Male wrens are fanatical, making several complicated domed structures, at least two or three and sometimes as many as ten, until a female finds this so impressive that she mates and lays her eggs in one of them. The unused nests are sometimes used for roosting, which is unusual because most other bird species only use nests to rear their young.
A few birds, including members of the crow family and some birds of prey, use the same nest every year, just repairing it and adding to it. Over time the nests can become enormous, like the osprey nests in Scotland or a jackdaw’s nest that I know of which fills a ten-metre chimney.
But most birds abandon their old nests and build a new one every spring. This is a defence against a build-up of parasites. There is competition for good nest sites, particularly among species like great tits or starlings that nest in holes or crevices. They will often use the same site every year but pull out the old nest and build a new one.
The typical bird’s nest is a cup-shaped object built in the branches of a tree, shrub or hedge. It’s strongly constructed of woven grass or other vegetation and lined with feathers, moss or sheep’s wool. But there are countless variations on the theme.
The song thrush lines its nest with a cement made from mud, rotten wood and dung. The goldcrest suspends its tiny nest below a branch high up in a tree using a cable of twisted spider’s web. Water-hens and grebes make floating nests of dead reeds and magpies and wrens add a roof to theirs.
Wood pigeons choose a small but leafy tree, often a hawthorn, and build a skimpy-looking platform of twigs. It’s so skimpy you can see the eggs through it when you’re standing underneath. But it’s cleverer than it looks because it supports a heavy bird with large eggs, even in the windiest weather.
Hen pheasants are sloppy nest builders, wriggling around in long grass and laying their eggs on the ground. But the finest nest-builder among Irish birds is the long-tailed tit which employs cobwebs to build an exquisite ball with an entrance hole. It is camouflaged on the outside with lichen and lined inside with thousands of tiny feathers.
* dick.warner@examiner.ie
a d v e r t i s e m e n t
This appeared in the printed version of the Irish Examiner Monday, April 11, 2011
