Tuesday, 4 April 2006

Climate and the elegant wagtail

The lengthening days and spring sunshine make my riverside walk to work all the more pleasurable.  The background chorus of singing birds lifts the spirit, something that is further enhanced by the sight and sound of grey wagtails, newly returned to this stretch of the river. At first glance the name ‘grey wagtail’ seems a confusing one; for, although this elegant bird sports a slate-grey back, it has a striking yellow breast and sulphur yellow undertail coverts. However, once you have seen a yellow wagtail, ­the choice of name seems a fair one. A sometimes-used local name for the grey wagtail is ‘water wagtail’ and this provides an accurate distinction between the two species. While the yellow wagtail is associated with lowland wet grassland, the grey wagtail is strongly tied to fast-flowing streams and rivers.

Although widely distributed across Britain, the grey wagtail has its stronghold as a breeding bird in the uplands, traditionally only moving into the lowlands in winter. Over the last hundred or so years the species has been noted increasingly as a breeding species across lowland Britain, nesting among tree roots or under bridges above water on faster stretches of river. The grey wagtail remains scarce in the east of England, with the first successful breeding attempt in Norfolk not recorded until 1923 (at Taverham Mill). Today some 20 or 30 breeding pairs are reported annually from within the county. One of the main reasons for this change in breeding range is thought to be climate change. As a year-round invertebrate feeder, the grey wagtail is susceptible to extended periods of cold winter weather, during which food is hard to find and mortality rates increase. The two severe winters of 1961/62 and 1962/63 are known to have had a big impact on the grey wagtail population. Since then, the run of mild winters has enabled the population within lowland England to increase.

Breeding starts very early in the year, with eggs laid from late March or early April, and this certainly ties in with the activity I have been seeing over recent days. The presence of the birds close to where they nested last year is revealed by the distinctive flight call, a metallic sounding ‘tzitzi’. The birds themselves can often be seen in flight, bouncing and undulating their way up- or down-river.  However, it is when seen on the ground that they are at their most elegant. The long tail is proportionally longer than that of our other wagtails and seems in constant motion as a bird walks about picking up small spiders or flies. On occasion one will fly up to catch an insect in flight, just like a flycatcher only with more balletic poise.

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