On Helgoland, the British Yellow Wagtail (Motacilla flava flavissima) used to breed in the 1920s and 1930s, but then disappeared due to rats. Since it is a scarce spring migrant with the occasional breeding record (the last in 1977).
On April 17th I was happy to add this taxon (regarded as a species in Germany) to my garden list, when the local sheep broke into the neighbouring garden, followed by a flavissima. The following day, the same happened again and I could see 2 males and a female flavissima as well as a male flava from my kitchen table. Together with Martin Gottschling I went out for photographing these birds and we noticed a Citrine Wagtail like rasping call – THE signal to check any Yellow Wagtail more closely, as there are many vagrant taxa from the south and east using this call. However, the flava male had already disappeared and only the 3 flavissima (2 males and a female) were present. While one male and the female called normally, the other male always used the Citrine Wagtail call, as far as we could see/hear.
This is the bird in question – looks like flavissima to me!
Sorry, my sonagram skills are still juvenile …
You can listen to a recording of the call >HERE<
So, could it be a Yellow-headed Yellow Wagtail (Motacilla flava lutea)? This taxon is still on the German list due to 2 records on Helgoland, which were recently rejected by the Helgoland Rarities Committee, as lutea and flavissima are not safely identifiable in the field and no call was recorded. These birds looked like lutea, but such extremes are apparently regularly recorded in the British breeding population of flavissima. So this time, it is the other way around: We have a bird only obvious by the rasping call. By the plumage features, I wouldn’t hesitate to call this bird a flavissima, though perhaps on the brighter side of the majority. However, is the call a safe ID-feature of this taxon?
Checking the literature, I found some hints only:
Alström & Mild (2003): Pipits and Wagtails of Europe, Asia and North America.
p. 281: “… Accordingly, vagrants outside their normal ranges cannot be identified with certainty, except perhaps by voice (see Voice).
p. 300-301: The call of flava, flavissima, beema and thunbergi … given both in flight and from the ground … is a rather loud pseeu, pslie, psie or similar …Also gives a slightly sharper psriee or tsriee (in combination with the above-descibed notes), which is possibly a less harsh variant of the alarm call (but is used as a normal flight-call).
The subspecies lutea apparently uses both ‘feldegg-type’ and ‘flava-type’ calls … We have not heard any lutea that switched between the two call-types (more research on the calls of lutea is needed).
Van Duivendijk (2011); Advanced Bird ID Handbook.
For lutea and flavissima no voice-feature is given, although in other taxa, the rasping call is mentioned in opposite to north-western Yellow Wagtail taxa
So, what does this tell us? Although flava and thunbergi might utter occasionally a harsher call, birds calling constantly like this should be of another taxon. Nevertheless, I think it is very unlikely that lutea and flavissima meet on Helgoland in a flock rather early in the year. A southeastern Yellow Wagtail I would expect to appear rather later in spring, as e.g. feldegg does, although there are some rather early records (e.g. last week). Southwestern vagrant taxa however seem to appear rather early in the year (there were already quite a few observations this spring in southern Germany).
To me this is just a flavissima. But if flavissima can call like this, then Rarities Committees should reconsider, if the call should be really the clincher for the ID of vagrant Yellow Wagtail taxa.