Monday, 30 April 2007

Ring Ouzels on passage

The last two weeks have seen very good numbers of ring ouzels at various sites along the North Norfolk coast. These birds, members of the thrush family, winter around the Mediterranean Basin and breed in upland areas across Britain and other parts of Europe. Given their preference for breeding sites situated on scree and boulder-strewn slopes, some 250m above sea level, it is hardly surprising that your only chances to see them within Norfolk come during their spring and autumn migrations. With their smoky black plumage, ring ouzels are superficially similar in appearance to a blackbird and, being of comparable size, there is the possibility of confusion between the two. However, adult male ring ouzels sport a large white crescent on their breast and have wing feathers edged with a greyish white. The crescent is absent in young birds, and less prominent in most females, but the feather edging should be sufficiently apparent to allow an accurate identification. To my eye, ring ouzels adopt a more upright posture, reminiscent of a fieldfare, than that seen in a blackbird.

Over the past two weeks we have seen a peak in the numbers of ring ouzels within the county, with small groups of birds dotted along the coast from Heacham and Holme to Winterton and beyond. These birds are likely to be en route to breeding grounds within Scandinavia; the British breeders having passed through the country several weeks earlier and arriving from a different direction. For these Scandinavian birds, the spring passage appears to be something of a leisurely affair, with individuals frequenting the same coastal scrub and dunes over several days. This provides them with an opportunity to feed and rest before migrating onwards to their final destination. In some years, males that have chosen to stopover here may indulge in a spot of singing, adding an unfamiliar song to the growing chorus of migrant songsters. The numbers of birds arriving during spring passage tend to be greater than seen during autumn and, in contrast to the pattern seen in autumn, there are also occasional records from well inland. Just last week, two were reported to me from near Diss. Although this pattern for inland records appears to have increased since the early 1990s, coastal sites are still favoured.

Like a number of other migrants, the ring ouzel population has been in decline and we have a seen a significant reduction in the size of the breeding range within Britain over recent decades. Although some of the causes of this decline may lay overseas, on the wintering grounds or migration routes, it is worth noting that acidification of breeding areas here may have reduced food availability and impacted upon breeding success.

No comments:

Post a Comment