Friday, 28 May 2010

Scratchy songster of the nettlebeds

The scratchy song of the Whitethroat can be heard from many of the county’s nettle and bramble beds at this time of the year. Numerous pairs haunt the rough cover of the forest’s snag lines – the tree roots and timber waste dragged into rows once a conifer plantation is clear-felled. Other pairs deliver their sharp ‘tchack’ alarm calls from patches of waste ground, where their delicate nest of grass stems is placed low in thick cover (usually between 30 and 60cm off the ground). A male Whitethroat will build several nests, each unfinished. Known as ‘cock nests’, these platforms of grass are often decorated with plant down or other ornamentation. The female will then select the nest site and help to finish the nest, lining it with hair and fine grasses, before initiating egg-laying. The buff-white eggs, of which there are usually four or five, have yellow-green markings overlaid by darker spots, the latter often forming a zone towards one end of the egg. Incubation begins once all the eggs have been laid, with most of the incubating being done by the female; the male does some but only the female incubates during the night.

This robust warbler does well here and the United Kingdom supports the fourth largest Whitethroat population of any European country. In favoured habitats the density of breeding pairs can be staggering but more typically numbers five or six pairs per kilometre square. Two of the nests that we are monitoring this summer are just 30m apart, with both birds at about the same stage of their nesting cycle. Most of the Whitethroats that are singing now will have arrived during the second half of April, with many discovering that the vegetation cover was somewhat late in developing. This will have placed early nesting attempts at greater risk of predation, with these nests easier to spot and hence more likely to be found by crows and other predators. Most Whitethroats are on eggs and the first chicks will not be far off, the only brood that most will produce this year.

Come the autumn and these birds will head south to wintering grounds in the Sahel region of West Africa. This part of Africa has been prone to devastating droughts in the past, the most significant of which produced a massive crash in the Whitethroat population. Numbers breeding in Britain fell by 77% between the 1968 breeding season and that of the following year, purely as a consequence of failure of the rains. Numbers have not yet recovered to anywhere near their former levels and continuing problems in West Africa, notably habitat degradation, suggest that they probably never will.

No comments:

Post a Comment