West Coast Wheatears
Over the past few weeks I have assisted a local ringer (Arne, who also sells some useful foldable net poles for ringing) at two of his local patches close to the Danish west coast. Both sites are located within the boundaries of Thy national park, one at an old farm site, surrounded by conifer plantation and the second on a long narrow peninsula (Agger Tange) which separates a fjord (Limfjord) and the North Sea.
During my two visits we caught three Northern Wheatear (Oenanthe oenanthe) known as ‘stenpikker’ in Danish, two at the farm and one at Agger Tange. On the 30th of April we caught two birds, one with a wing 93mm (referred to as W1 for ease of reference) and the second with a wing of 92mm (W2) together, next to each other in a net, at the farm site.
Firstly I was surprised at how similar the two birds were, compared to the images presented in some field guides. It appears that W1 is a male, with silver/blue-grey crown, nape, mantle and back and a while supercilium, together with black lores and wings. However the ear coverts are quite pale, more brownish than other photos and descriptions suggest. W2 had, in general, a similar pattern, but appears “dirtier” with all features less clear cut, more brownish wings, buffier underparts, paler cheek patch etc. which matches the BWP description for females.
In terms of moult and ageing, Jenni & Winkler (1994) informed me that juveniles undergo a partial post juvenile moult (all lesser & median coverts, a variable number of greater coverts and possibly the innermost tertial, carpel covert and smallest alula), while adults perform a complete postbreeding moult. However things get a little more interesting (exciting!) as a small percentage of both adults and second years under go a very restricted partial prebreeding moult (may include lesser & median coverts, inner greater coverts and tertials). This means it may be possible to see 3 generations of feathers in some second year birds; juvenile, post juvenile and prebreeding! This reminds me of many happy days ringing chiffchaffs in Catalonia in the spring of 2014 – exciting times!
Firstly a close look at the male wing (W1). It appears that the inner greater covert has recently been renewed (prebreeding) identified as having a broad greyish brown fringe (see arrow). Some median and lesser coverts may also have been replaced, but it is difficult to see due to my thumb! The remainder of the wing appears to be postbreeding, therefore I assume it to be an adult (3rd calendar year or older).
The female (W2) wing appeared to be in a similarly good condition with dark feathers, but with a more brownish black colour when compared to the male. It is possible that the inner 3 median coverts have been renewed in the prebreeding moult (greyish fringe compared with buff fringe, see arrow). With the presence of two feather generations and the general condition of the wing, I think it could also be an adult (3rd calendar year or more), but I would love to see some second years to compare! Interestingly she had also recently renewed 3 tail feathers (identified as longer with buff tips) on the left hand side, suggesting accidental loss.
On the 8th of May at Agger Tange we caught a another wheatear (W3), with a much longer wing, (104mm, weight 31g). It appeared to be a male, with clean black lores, but showed more brownish tinges in the back, head and mantle.
I must admit, I got quite excited while examining the wing of this bird. It is possible that there are three feather generations in the greater coverts (GC)! The outer greater coverts (1-8) appear to be juvenile, brownish, loose in texture, with pale, worn buff edges, GC9 appears to be post-juvenile (PJ) with a much darker, black centre and buff edge, while GC10 appears to be prebreeding with a greyish fringe as seen in W1 and W2 above (see red labels & arrows below). This presence of 3 feather generations suggests a second calendar year bird (born last year). (Comments welcome on this!)
According to Birds of the Western Palearctic (BWP, 2004) there are four subspecies of Northern Wheatear in the the Western Palearctic. Two are commonly reported in Denmark; the nominate European race (O. o. oenanthe) which breeds in Denmark (ca. 2,000 pairs in 2011; DOF), and the Greenland race (O. o. leucorhoa) which passes Denmark on migration from overwintering grounds in western Africa to breeding grounds in Greenland, Iceland and eastern Canada. It’s worth a mention that research using geolocaters has shown that wheatears make one of the most impressive migration journeys for a passerine.
The Greenland race (leucorhoa) is noticeably larger than the nominate (oenanthe), with bill, wing and tail 15-20% longer and legs 20-30% longer (BWP, 2004). The first two birds we ringed (W1 male and W2 female) had shorter wings (93 and 92 mm respectively) compared with the last bird caught (W3, 104 mm). Wheatears of the nominate subspecies in Denmark were reported to have wing lengths of 94-99 mm (males) and 89-95 mm (females) with slightly smaller birds reported in Norway and Sweden (males 92-99 mm, females 91-97 mm) (BWP). Wing measurements from wheaters in Greenland are much larger (males 101-109, females 99-105) but slightly smaller among breeding birds caught in Iceland (males 99-107, females 96-103) (BWP, 2004). Based on wing measurements it appears that W1 & W2 are of the nominate species, while W3 belongs to the Greenland race (leucorhoa).
In terms of plumage, BWP states leucorhoa from east Canada and Greenland show less blue and apparently no silver or white tones on grey crown and back, with much richer and darker, more uniformly coloured underparts (possibly observed in photo above). However attempting to compare colours in photos taken on different days, with different light conditions, and in different positions, is less than ideal. Also there appears to be age related differences in sexual plumage to consider (first spring males more female like with duller dirtier tones). BWP also states that Icelandic birds are intermediate in size and appearance between the nominate and birds from east Canada and Greenland, confusing matters even more!
During my absence, Arne managed to catch two male wheatears, one of each subspecies. The photos clearly show the size difference between the nominate (left) and Greenland race (right).
Differences in underpart colour is also evident, with the Greenland bird (right) showing a more warm buff colour on the chest / belly that extends down towards the vent.
References & links
Birds of the Western Palearctic Interactive DVD (2004). Gostours; 2.0.3 edition.
Jenni, L. & Winkler, R. (1994): Moult and Ageing of European Passerines. Academic Press, London, UK
Arne’s online webshope – selling net poles