Tuesday, 30 January 2018

'North American' Horned Lark - Staines Reservoir

A 'North American' Horned Lark was present on the causeway between the North and South Basins of Staines Reservoirs from 19th to 28th November 2017 and while obviously an interesting bird I had no opportunity to go and see the bird. After an absence of a few weeks when the bird was, presumably, feeding elsewhere within the local area the bird was relocated on 22nd January and this time I had a chance to visit the bird. I parked on Town Lane adjacent to the eastern entrance to the causeway and walked onto the causeway, there were around 10 birders and it was immediately apparent that the bird was on show. I bowled up and there it was feeding on the south side of the causeway only 20m or so away. Over the couple of hours that I was there the bird showed well but in terrible light conditions on this still and sunny day. It spent much of its time picking through the weeds on the reservoir revetment. My photos of the bird are fairly poor due to the light but do show the characters that indicate that this is an 'North American' Horned Lark.

HBW Alive currently recognises 28 subspecies over its vast range (other authorities recognise a varying number of subspecies). These are separated based mainly on differences in size, ground colour (partly determined by local soil colour) and pattern. A recent molecular study suggests that taxa in the Old World break into five species and surely more species could be recognised, both in the Old and the New World, with further work. HBW Alive and IOC currently treat all subspecies under one species known as Horned Lark.

In North America there are currently 11 subspecies recognised by HBW Alive. Alpestris is the nominate subspecies within the North American group and so if split would be the 'parent' species with the others being the subspecies of this. Most of the North American subspecies are unlikely to occur as vagrants as they are either short-distance migrants or are resident. Those most likely to occur as vagrants are alpestris and hoyti. Alpestris breeds in eastern Canada and the eastern USA with northern populations wintering in the eastern USA. Hoyti breeds in northern Canada and winters in the northern USA.

The field characteristics of these taxa seem to be poorly described but in essence alpestris has a greater extent of yellow in the face, and particularly in the supercilium, while hoyti has the yellow restricted to the throat with a white supercilium. The bird at Staines thus seems to fit hoyti best but without DNA analysis this seems unlikely to be proved. From the subspecies 'flava', our Shore Lark, differences are based on the limited extent of yellow in the face, the pinkish tones to the plumage and perhaps the more speckled breast but all differences are modest and perhaps variable/clinal.

There seem to be two possible records of 'American' Horned Lark in the UK (with other claims elsewhere which don't seemed to have gained much traction), these are:
  • St Agnes and Tresco, Isles of Scilly - 2nd to 31st October 2001
  • Askernish, South Uist - 9th to 11th October 2014
The Isles of Scilly record was never submitted and current thinking is that it may not have been 'North American' Horned Lark while the South Uist record remains in circulation with the British Birds Rarities Committee (BBRC). A summary of BBRC's current stance on Horned Lark can be found here

Here are a few links to articles discussing the identification of 'North American' Horned Lark:

The identification and taxonomy of this species remains complex and it would appear that a great deal of further work is required before the North American subspecies are split.