Sexing Citrine Wagtails, it sounds pretty easy, doesn’t it? And yes, typical and representative birds rarely causes any trouble in this respect: Smart looking males with bright and clean lemon head, ear-coverts and breast combined with a well-developed black nape collar signals their gender rather promptly. The same goes for most females showing a duller yellow front with darker olive-greyish crown and ear-coverts and a pale nape.
Rather typical female (probably adult due to apparently rather fresh and well-kept dark primaries and primary-coverts) showing greyish olive crown and ear-coverts. Russia, June. Photo: Magnus Hellström.
Life would be simple if the issue had stopped there but, rather stimulatingly, it doesn’t. More intermediately patterned individuals are sometimes seen and such birds often causes discussions in the birding community. This challenging problem is caused by the fact that some first summer (2cy) males shows less developed male characters while, conversely, some adult (3cy+) females attain a more colourful and male-like plumage than normally seen. Therefore, if seen under good conditions, there are means to collect further clues: change focus and start with ageing the bird. If 2cy, it is likely that the bird is a dull male, and if 3cy+ we have good reasons to assume it’s a bright female.
Drab looking (and female-like) 2cy male that sang and held territory for a week. Aged as 2cy by still showing juvenile worn and bleached remiges, primary-coverts, alula and outer greater coverts. Sweden, May. Photo: Göran Bength.
The Citrine Wagtail – like its closest relatives – unfortunately shows a moult pattern where both the young and the adult birds replace their body contour feathers during winter (in a so-called partial pre-breeding moult). This moult does not include remiges, but it does include a number of greater coverts and tertials. This means that more or less all birds (regardless of age) in the spring will exhibit a moult contrast in the wing. Thus, in contrast to many other passerine species, the mere presence of a contrast is of no use for ageing. Instead, concentration should be directed to the parts of the wing that was not replaced during the winter, i.e. primaries and primary-coverts. Both 2cy and 3cy+ birds attained these feathers during the previous summer, but since juvenile feathers are of lower quality than subsequent generations, 2cy birds in the spring will show more worn and brownish primaries and primary-coverts than 3cy+. Mind, however, that also adult birds are getting quite worn by spring, but still usually retains a darker (dark greyish) feather colour. In other words, it is the degree of wear that has to be assessed.
A rather difficult bird, but although the retained parts of the wing (some tertials, some greater coverts, alula and remiges) has become slightly worn they still give an adult appearance. In my opinion this is most likely a 3cy+ bird and therefore reasonably a female. Russia, June. Photo: Magnus Hellström.
As seen in the photos, Wagtails have a wing structure that often makes primaries and primary-coverts hard to study since they are covered by other feather tracts. This, of course, complicates the situation a bit, and it usually requires good observation conditions to be judged properly. However, the worn and brownish wing in many 2cy birds is often rather eye-catching, and it’s often easier to feel safe ‘nailing’ a 2cy bird than an adult one. In the end, this will probably lead to an over-representation of 2cy being aged (as proportionally more 3cy+ will be left un-aged). This is probably inevitable but can be useful to keep in mind.
Another one, giving a slightly sullied impression on crown and ear-coverts and completely lacking black in nape. Retained remiges gives a brownish and worn juvenile impression, and points towards 2cy. Being a 2cy the plumage would favor an ID as a male, and this was also supported by behavior as it defended territory on breeding ground. Mongolia, June. Photo: Magnus Hellström.
FOOTNOTE: If we aim for complete accuracy, the above statement that the presence of a contrast is of no use for ageing, deserves a deeper comment. Adult individuals undergo a complete moult after breeding, and after that the entire plumage is of the same generation. As mentioned above, the partial moult in the following winter creates a simple contrast among the coverts. Nothing strange so far. The juveniles, on the other hand, starts their life with a partial moult soon after fledging, and then, according to the same principles, receives a moult contrast before autumn migration. During winter they, again, conduct a partial moult. Sometimes (but not always) this winter moult include fewer coverts than the previous (post-juvenile) moult. Such a strategy results in a wing with two moult contrasts, since the outermost coverts are still juvenile, the central ones derived from the post-juvenile (summer) moult, and the innermost from the pre-breeding (winter) moult. Establishing three generations of coverts (two moult contrasts) is usually very difficult in field, but if we for some reason manage to do it, it is another good indication of a 2cy bird.
A rather dark crowned but brightly yellow-faced bird with quite clean ear-coverts. The photo is slightly out of focus and the bird is wet from rain, but wear in primaries supports 3cy+ (and the bird appeared adult also in field). As adult this should be a safe female. Russia, June. Photo: Magnus Hellström.