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Key features  keep checking!

On Friday 2 November 1984, René van Rossum discovered a Spectacled Warbler Sylvia conspicillata at the head of the South Pier near IJmuiden. It concerned the first sighting of this Mediterranean species for the Netherlands (van IJzendoorn & van Rossum 1985). About three years later, when I was nine years old, I started my birding career and IJmuiden became my favourite local patch. Over the years, I encountered a wide variety of birds, including several rarities but – of course – no Spectacled Warbler. I kept wondering how to increase my chances of finding and identifying one.
 
Carefully checking every Common Whitethroat is a start. On plumage alone both species can be difficult to separate. This is in particular true for first-year birds and females. Knowledge of plumage features is thus essential. But other characters, like size, structure, vocalizations and behaviour, are important too. In fact, they might well attract attention first. Clearly, any small and short-winged Sylvia, hopping around on the ground between low vegetation and giving rattling calls, deserves close examination!    

Because Common Whitethroats and other warblers all too often disappear from view before you even have time to lift your binoculars, focussing on key features makes a huge difference. Judging the size and tail pattern of every Sylvia being flushed could eventually pay off. Spectacled Warbler is after all noticeably smaller than Common Whitethroat and typically shows a slightly more rounded tail with almost completely white outer tail feather (t6) and prominent white tip of t5. In many Common Whitethroats the outer web and tip of t6 and tip of t5 are off-white, while much of the inner web of t6 is greyish. When perched, a short primary projection and almost uniform rufous wing-panel can be striking in Spectacled Warbler, as well as some other features mentioned in most field guides.  

The rattling calls of Spectacled Warbler could be mistaken for Eurasian Wren or perhaps other rare passerines. Common Whitethroat, however, has no such call. Scrutinizing every odd rattle is surely a good habit, especially when heard in unusual habitats like salicornia-vegetated saltmarsh. Rattles given by Spectacled Warbler last for c 0.5-1.5 sec with c 29 notes per sec, sometimes delivered at a slightly stuttering pace. Eurasian Wren rattles are usually shorter but there is much overlap.

Finally, learning Spectacled Warbler song by heart could pay off as well. Overshooting males in spring can hold territory in suitable habitat and are likely to be discovered only by the trained ear. Compared with Common Whitethroat, song phrases are usually short (less than three sec long) and plain, built up of clear whistles and scratchy and chirping elements. Some start with a few notes reminiscent of Crested Lark. Dismissing a singer as a European Stonechat is a real risk. This species also occurs in open landscapes with scattered knee-high vegetation and utters rather similar simple songs. Also Common Linnet can sound confusingly alike.

Common Whitethroat intobirding.com

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Published 6 March 2018