Tuesday, 8 November 2011

Pallid Swift makes for tricky identification

The final week of October saw many Norfolk birdwatchers turn their attention to the skies above some of our coastal towns. Reports of one or more Pallid Swifts set pulses racing, as people grappled with the tricky task of clinching an identification of this rare visitor.

Up until fairly recently, the commonly held view was that any pale swift, seen off the back of a warm southerly airflow in late October or early November, was likely to be a Pallid Swift. Although this species breeds throughout the Mediterranean, from Greece west to Iberia, it is absent from many parts and rare in others. It has only recently been found breeding on the Atlantic coast of France and also in Switzerland, highlighting that our knowledge of the species is still far from complete.

The difficultly of securing an identification comes about because of potential confusion with late Common Swifts, either juveniles or birds of the Asian race pekinensis, both of which look similar to Pallid Swift. Many of the key identification features are difficult to pick out on a bird that is not only moving but also often viewed in silhouette against a paler sky, making the assessment of colour difficult. There is one structural feature that can prove helpful, however, as the two outer wing feathers in Pallid Swift are of similar length, giving the appearance of a blunt wing-tip. In Common Swift, the outer of these two feathers is longer, giving the wing a more pointed appearance.

The presence of any swift in these late autumn skies gives pleasure enough, a last glimpse of summer’s sprite and a sense that part of summer lingers still. Our Common Swifts will be in Africa by now – in fact many will have been there for some weeks – their brief sojourn to Britain a faded memory. Unlike our Common Swifts, the Pallid Swift is double-brooded, squeezing in a second nesting attempt from late July which delivers newly-fledged young from early October. It may well be these individuals that reach southern and eastern Britain on the back of strong southerly airflows, such as the one we experienced in the first few days of November.

That there should be discussion over the identity of those Swifts seen here over the last couple of weeks, highlights the complexity of movements made by these cracking birds. It also underlines the identification skills needed by birdwatchers seeking to add a new species to their list. It will be interesting to see how the recent flurry of records is treated by the Norfolk Rarities Committee, a group of knowledgeable individuals who assess records of rare birds by looking at the evidence provided in support of the claim that has been made. 

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