Ageing and sexing of White Wagtail (Motacilla alba alba) during autumn(al migration)

12^th May 2021 | Ringing

» Česká verze zde (Czech version): Určování stáří a pohlaví konipase bílého evropského (Motacilla alba alba) na podzim(ním tahu).

This article was originally published in the bulletin of Czech ringing central in short version (2021/31; pdf in Czech ) and in long version on my website in Czech. This is an English translation of that article. It was meant as an aid for ringers who would like to participate in a call to ring more White Wagtails during autumn migration. This species is trapped rather randomly in Czechia because it is not an easy species to trap during the breeding season. But this changes markedly during its migration and there is still a lot to learn.

Nonetheless, this article might be of interest to anyone who needs to sex or age a White Wagtail during autumn/winter, either a ringer or birder. It also contains information about sexing which, as far as I know, has not been published elsewhere before.

If you are a licensed ringer and would like to try to participate in ringing migrating wagtails, send me a request and I will send you a methodological article where you can find information on how to do it. It is very easy. Contact info here .

You can find more photographs of this species on this website in the Gallery section: Motacilla alba.

Each photograph in this article is accompanied by a number in brackets – a link to the gallery (opened in a new tab) where you can see other photos of that individual.

Abbreviations:

greater coverts: GC
median coverts: MC
lesser coverts: LC
primary coverts: PC
carpal covert: CC
primaries: P
secondaries: S
tertials: T
alula: Al

Moult

Adult: SC, wp
Juvenile: sp, wp

Postjuvenile moult

Wagtails in first year of life start post-juvenile moult soon after the juvenile plumage finishes growing. During the post-juvenile moult wagtails moult all their body feathers, LC, MC and no to all GC. In half of the cases also some rectrix are moulted. Flight feathers are not part of the post-juvenile moult except for T, which might be moulted all. On extremely rare occasions also some P and S might be moulted, too. Only very few such cases are documented (two in this gallery) and it is worthwhile to photograph such individuals well. Post-juvenile moult might prolong well into October and it is not unusual to find moulting wagtails during the migration, probably from late broods. Last feathers to moult are feathers of head, belly and back. Some first-year wagtails from more northern populations might be migrating in complete juvenile plumage.

Ca. 75 % of birds moult at least one GC (average = 6.1; median = 7; n = 153). The number of moulted greater coverts lowers during the autumnal migration probably in relation to the progress of migration of more northerly populations and by the onset of migration of wagtails from late broods (fig. 1.1). Half of the remaining 25 % does not moult any of the GC, the second half moults all ten. Birds which moult higher number of GC very often also moult some T.

Fig. 1.1: Number of moulted GC in 1CY (euring: 3) White Wagtails during the autumnal migration (years 2019 and 2020 combined). Line segments shows minimum and maximum values, circles mark average value and triangles median values. Numbers above graph show sample size in corresponding week. The last week number is based only on one individual which creates the illusion of rising trend.

Postbreeding moult of adults

After breeding, adult wagtails moult completely and this moult can be prolonged into October. Moult of flight feathers starts with P 1 and progress in one wave divergently (S1 is shed when P moult progresses towards P5–6). At the beginning of the migration, it is not uncommon to find individuals with moulting flight feathers – those are almost exclusively adult birds (1CY+, euring: 4). Last feathers to moult are feathers of head and belly, similarly to 1CY (euring: 3) individuals. Birds moulting some body feathers can be encountered exceptionally also by the end of October.

Ageing

Knowledge of moult is essential to correctly age (and then also sex) White Wagtails. White Wagtail is not a particularly tricky species to age during the autumn, but some individuals might be more difficult and therefore erroneously identified. Especially when one age them rather “automatically” or is using just one criterion. When ageing, we search primarily for moult patterns of GC, MC and moult of T and flight feathers in general. On the other hand, tail feathers are usually not very helpful in ageing^[1].

White Wagtail can be aged also using scoring skull pneumatisation. That is rather difficult in this species, though, and usable only until mid October.

Adult birds: 1CY+ (euring: 4)

Adult individuals can be recognized by completely moulted wing. All of the GC are new and fresh with dark (black) centres and broad unworn edge. No moult contrast is present in GC (beware of slightly different colour of outside GC which can resemble a moult limit, see fig. 2.1.1) and they do not contrast in structure with MC. Flight feathers are new, fresh and dark with dense structure. No moult limit is present in T (beware that T 7 is always darker than T 8 and 9) or between T and S. P forming the wingtip are wide and round (fig. 2.1.3). PC are wide with dense structure and round end. Tail feathers are dark, fresh, wide and with blunt tip (even though this criterion is not always useful).

If an individual moulting flight feathers is trapped (except for T), it is almost invariably an adult (fig. 2.1.2). But beware the exceptional 1CY (euring: 3) birds with extensive post-juvenile moult, see Unusual cases).

Fig. 2.1.1: M 1CY+ (euring: 4); Wing of an adult wagtail, note the colouration of GC, especially slightly different colour and pattern of GC 1–3 and 7–10 which might recall a moult limit. Whole wing postbr. [CZEP19-452]

Fig. 2.1.2: F 1CY+ (euring: 4); Active moult is – apart from extremely rare cases (see text) – a good indication of an adult bird. LC, MC, part of PC, P 1–5, S 1–6, T 7 prebr., rest of the wing postrbr. (GC are growing). [CZEP20-398]

Fig. 2.1.3: Comparison of colour and shape of P of 1CY (euring: 3) bird (left) and 1CY+ (euring: 4) bird (right). [CZEP20-395, CZEP20-482]

First-years: 1CY (euring: 3)

First-year individuals can be recognized mostly by having a moult limit in GC. Compared to post-juvenile ones, juvenile GC are shorter with brown centres and have sharply defined light edge. Juvenile GC are usually also more worn. On the other hand, post-juvenile GC have dark brown to black centres which smoothly transition to wide light edge. N.B.: the three inner post-juvenile GC are always a bit longer and greyer and may simulate a moult limit (fig. 2.2.1 and 2.2.2).

Individuals that did not moult any of the GC can be recognized by contrast of juvenile brownish GC and moulted MC, that have dark (black) centres with wide light edge (fig. 2.2.3). Ageing birds with all GC post-juvenile is a bit more tricky. We focus on the contrast between post-juvenile GC and juvenile remiges (fig. 2.2.4 and 2.2.5). Those are quite bleached by October and start to be pretty worn, too. Especially P forming the wing tip are narrower and more pointed than post-juvenile P (fig. 2.1.3).

Moult limit in T can be used for ageing, too. Post-juvenile T with dark centres sharply contrast with surrounding juvenile remiges. Beware that T 8 and 9 always look a bit different (lighter in colour) than T 7 which can resemble a moult limit. PC can be also supportive in ageing. PC are rarely (close to never) moulted during post-juvenile moult. Juvenile ones are narrower, more pointed, lighter and less dense than adult ones (you can compare them with e.g. post-juvenile GC).

Tail feather of wagtails are not usually useful for ageing. If the tail is in good shape, we can use it as supporting criterion. Juvenile tail feathers are rather brown, often worn, narrow and pointed. We can find a moult limit in tail, too. Post-juvenile rectrices are black, wide and with blunt tip (fig. 2.2.6). It is not uncommon that whole tail is moulted, and it is not useful for ageing, then (fig. 2.2.7).

Fig. 2.2.1: M 1CY (euring: 3); wing of a 1CY male after quite restricted post-juvenile moult. Note the moulted T 7. LC, MC, GC 7–10, T 7 postjuv, rest of wing juv. [CZEP20-394]

Fig. 2.2.2: F 1CY (euring: 3); wing of a 1CY (euring: 3) female after a post-juvenile moult that was quite average in extent. LC, MC, GC 5–10 postjuv., rest of wing juv. [CZEP20-498]

Fig. 2.2.3: F 1CY (euring: 3); wing with all GC juvenile. Their dark centres contrast nicely with post-juvenile MC with dark centres. LC and MC postjuv, rest of wing juv. [CZEP19-407]

Fig. 2.2.4: M 1CY (euring: 3); bird with all GC post-juvenile – their dark black centres contrast with brown juvenile remiges. This bird also moulted all T (T 7 is still growing). GC 1–10, LC, MC, CC, T 7–9, Al 1 postjuv, rest of wing juv. [CZEP20-399]

Fig. 2.2.5: F 1CY (euring: 3); same case as in fig. 2.2.4. Here, you can clearly see the worn tips of P forming the wing tip. Such wear is rare in adult birds in the end of autumn. GC 1–10, LC, MC, CC, T 7–9, Al 1 postjuv, rest of wing juv. [CZEP20-416]

Fig. 2.2.6: F 1CY (euring: 3); in this case you can clearly see a moult limit between post-juvenile central pair of rectrices and rest of the tail which is juvenile. [CZEP19-406]

Fig. 2.2.7: F 1CY (euring: 3); individual with completely moulted tail – all feathers are post-juvenile. [CZEP20-393]

Juveniles: 1CY juv (euring: 3J)

Juvenile plumage of White Wagtail is very typical and unlike that of adult or first-winter birds. The most striking difference are grey cheeks and dark grey – not black – breast band. Juvenile contour feathers are typically loose in structure and are quickly worn. During the migration, most wagtails have already finished their post-juvenile moult and if not, are in its final stages with last traces of juvenile plumage (mostly on head, belly and breast). If you can recognize them, you can be sure, you’re looking at a first-year bird (1CY, euring: 3).

Fig. 2.3.1: M 1CY juv (euring: 3J); a young male in final stage of its post-juvenile moult – there are still many juvenile feathers on his head and breast (grey feathers in otherwise black breast band). [CZEP19-401]

Fig. 2.3.2: F 1CY+ (euring: 4); even adult birds can be seen moulting and migrating, usually in some very late stage of post-breeding moult. Very worn old feathers can look like juvenile ones, but age of this bird can be easily told not only because of still visible parts of breeding plumage (black breast band) but also because of the presence of moulting remiges (see fig. 2.1.2). [CZEP20-398]

Unusual cases

Exceptionally we might encounter a young bird with unusually extensive post-juvenile moult which included also some of the remiges. Because such cases are extremely rare, these are worth documenting. This can either be just one remex moulted out of usual sequence which then contrasts with surrounding juvenile remiges (fig. 2.4.1). Or very exceptionally, there can be more than one moulted remex and in the very rare case such individual moults also all GC it can resemble an adult during a wing moult (fig. 2.4.2).

It is worth noting that such cases are truly exceptional. As far as I know, the individual CZEP20-495 (fig. 2.4.2) is the only documented case of more extensive post-juvenile moult in White Wagtail. Therefore, it is worth documenting all such individuals you may come across.

Fig. 2.4.1: M 1CY (euring: 3); young White Wagtail which unusually included into post-juvenile moult also one S. LC, MC, GC 4–10, S 5, T 7–9 postjuv, rest of wing juv. [CZEP20-409]

Fig. 2.4.2: F 1CY (euring: 3); young individual with exceptionally extensive post-juvenile moult including several P and S. LC, MC, GC, CC, PC 1–2, Al 1–3, P 1–4, S 1 and 5–6, T 7–9 postjuv, rest of wing juv. [CZEP20-495]

Sexing

Sexing White Wagtails in autumn is surprisingly nontrivial, especially in first-years – much of the literature suggest not to sex them at all. But using a combination of following criteria it is possible to sex most of the individuals you are likely to encounter. Always start by ageing, as you can avoid sexing wrongly young males and old females.

Size dimorphism

Apart from being sexually dichromatic, White Wagtails are also sexually dimorphic in size, and quite considerably actually – males are bigger than females. This dimorphism is especially pronounced in two easily measured morphometrics – wing length and body mass (tab. 3.1, fig. 3.1.1 and 3.1.2). Wing length seem to be more reliable as body mass depends also on the amount of deposited fat and can be more variable.

Tab 3.1: Distribution of wing length and body mass in two groups of wagtails. Left are wagtails of known sex (molecularly, see Material & methods), right wagtails which were sexed based on photos (including those of known sex).

Obr 3.1.1: Boxplots showing differences in wing length (left) and body mass (right) between males (blue) and females (red) of White Wagtail. In each plot there is a lighter colour pair which depicts individuals of known sex on the left, and darker colour one which depicts individuals sexed by photographs (see Material & methods for details). Box shows 50 % of all observations (line marks median, cross marks average value), whiskers shows range of maximum and minimum values and individual points show outliers. For sample size see tab. 3.1.

Obr 3.1.2: Scatterplots showing differences in wing length and body mass between males (blue) and females (red) White Wagtails. On the left only individuals of known sex, right individuals sexed by photographs (see Material & methods for details). For sample size see tab. 3.1.

For wing length, there seems to be a division line at 90 mm which reasonably reliably sex most birds – males (≥ 90 mm) and females (< 90 mm). Similarly, 22.5 grams can sex most birds, too – males (≥ 22.5 g) and females (< 22.5 g). Even though expected variability is higher in body mass (because of fat scores in autumn are very similar among birds, actually), both body mass and wing length seem to sex correctly ca. 82 % of birds. Do not consider these values as definitive and without exceptions. Use them rather like supporting criteria when sexing birds. When sexing, remember that young males have shorter wings – up to 2 mm shorter than older ones. For females, the difference seem to be much smaller but on my dataset statistically non-significant (fig. 3.1.3).

Obr 3.1.3: Boxplots showing differences in wing length between young and old females (red) and males (blue; young individuals indicated with light colours, old individuals with dark) of White Wagtails. While older males have wing on average 2 mm longer than young ones, the difference between young and old females is statistically non-significant. Apparent difference of 1 mm in female average values is caused mainly by an exceptional and probably very old female with very long wing. Box shows 50 % of all observations (line marks median, cross marks average value), whiskers shows range of maximum and minimum values and individual points show outliers. Sample size left to right: 28; 16; 23 and 26 individuals.

Head and breast pattern

Colouration of head (cheeks, forehead and crown) and breast is usually recommended as a good way how to sex White Wagtails in autumn. But the variability in coloration is great and it is possible to sex only the most extreme birds. Personally, I do not recommend using it. Among the “typically” coloured individuals (that means individuals as described in literature, fig. 3.2.1), there are almost as many “less typical” ones (fig. 3.2.2). Those either do not fit in any category or look like the opposite sex altogether.

F 1CY (euring: 3): Nape and crown grey or with little black, white on forehead not rather limited and “dirty”, black breast band relatively narrow, cheeks with yellow wash. Females with more black on crown are not uncommon including extensively black individuals without yellow wash on face.
M 1CY (euring: 3): Crown blackish grey or almost black, white on forehead wider and more “clean”, black breast band broad. But, also males without black on crown occur – they usually have broad breast band.
F 1CY+ (euring: 4): Very variable, usually resembling 1CY (euring: 3) males, but black usually more intensive and greater in extent, breast band comparable or wider. Also, adult females with grey crown exist. White on forehead extensive, but often “dirty” with dark grey or black feathers. Yellow wash to face often present.
M 1CY+ (euring: 4): Usually extensively black on crown and white on forehead wide and without any black feathers, breast band relatively widest of all categories. Unlike other, adult males usually lack any yellow wash to face and therefore has white cheeks. But adult males with grey crown, “dirty” forehead and/or greyish cheeks occur, too. Those resemble adult females. Yellow wash least frequently observed, but can be present, too.

Fig. 3.2.1: “typical” representatives of males and females White Wagtails. From top to bottom: F 1CY (euring: 3), F 1CY+ (euring: 4), M 1CY (euring: 3) a M 1CY+ (euring: 4). From top to bottom: [CZEP20-416, 471, 483, 485]

Fig. 3.2.2: less typical but not less common(!) coloured individuals of White Wagtail. From top to bottom: F 1CY (euring: 3; extensive black on crown, white cheeks), M 1CY (euring: 3; lacks almost any black on crown but wide breast band present), F 1CY+ (euring: 4; lack of any black on crown is not uncommon even in adult females). M 1CY+ (euring: 4; colour of crown and cheeks resembles adult female, yellow wash to face ca be seen also in adult males). From top to bottom: [CZEP20-495, 492, 478, 410]

Coverts

The best criterion to sex White Wagtails seems (moulted) GC to me, which very reliably distinguish males from females in both age classes, including those that cannot be sexed based on head colouration or morphometric measurements. However, there are difficult cases, too. Very few individuals are hard to sex and if other criteria do not help, it is better to leave such individuals not sexed. Also, sexing by the colour and pattern of GC in individuals with all GC of juvenile type, cannot be recommended as it is not entirely reliable.

Coverts of females

Adult and post-juvenile GC of females have narrow edge which is rather light grey or dirty white and the asymmetric pattern of this edge does not form high “step” on inner GC like in males. Centres of GC are rather lighter than in males (brown-black or greyish-black). Similar differences in colour and pattern can be found on MC. Individuals with no GC moulted is better not to sex based on GC. Some males with all GC juvenile can resemble females based on MC pattern (see Coverts of males).

Exceptionally, some adult females can exhibit coverts resembling those of males, but these are never truly male-like in details (not so clean edge or with lighter centre). Therefore, we always compare also other criteria (fig. 3.3.3).

Fig. 3.3.1: coverts of 1CY (euring: 3) females. Left: all GC juvenile, LC and MC post-juvenile, and even though typically female looking, it is better not to sex such individuals based on pattern of coverts (compare with fig. 3.4.1). Right: all GC post-juvenile. [CZEP20-479, CZEP20-416]

Fig. 3.3.2: coverts of 1CY+ (euring: 4) females. Typical pattern and examples of variability. [CZEP19-418, CZEP20-499]

Fig. 3.3.3: nontypical and difficult cases. Left: very broad edge to GC and MC. Recognisable as female because of colour of centres of GC (not black but dark grey) and colour of their edges, which are rather dirty grey than pure white. Right: very dark coverts with almost white edges resembling coverts of males. Recognized as female because of rather narrow edges and quite low “step”. Both cases F 1CY+ (euring: 4). [CZEP20-478, CZEP20-471]

Coverts of males

Adult and post-juvenile GC of males White Wagtail have broad and clean white edge, and especially on inner coverts the asymmetry of white edge creates high “step”. Centres of these coverts are very dark (black). Same colour and pattern show also adult and post-juvenile MC. Especially in males without any GC moulted, MC can resemble those of females (fig. 3.4.1). As a rule, it is better not to sex birds with all GC juvenile based on the colour and pattern of GC.

Fig. 3.4.1: coverts of 1CY (euring: 3) males. Left: all GC juvenile, LC and MC post-juvenile but not exceptionally brightly coloured – such individuals is better not to sex (compare with fig. 3.3.1). Right: All GC post-juvenile. [CZEP20-492, CZEP20-399]

Fig. 3.4.2: coverts of 1CY+ (euring: 4) males. Typical pattern and examples of variability. [CZEP20-491, CZEP20-482]

Fig. 3.4.3: nontypical and difficult case of 1CY+ (euring: 4) male. GC seem rather female like with lighter coloured centre and quite grey and narrow edge. MC has more male like “step”. Colour of head and morphometry indicates a male (wing length 92 mm, body mass 25.4 g) which was confirmed by molecular methods. Sexing such individuals is rather difficult and better not done in the field. [CZEP20-480]

Conclusion

Ageing White Wagtails in autumn is not extremely difficult. We focus mainly on moult of coverts and remiges. Most of first year individuals have moult limit within GC. Beware of individuals without such moult limit. Even those can be aged with some experience, though. Very difficult individuals to age are quite a rare sight during the autumn.

After ageing we can proceed to sexing. Unlike ageing, sexing is far from easy and require some experience. The traditionally used main criterion – the coloration and pattern of head – is far from reliable and hugely overlaps between the two sexes. Extremely coloured birds can be sexed this way, but the risk of error is still too high. On the other hand, colouration and pattern of (moulted) GC seems to be very reliable to me. As far as I know, this is the first time GC are used for sexing in this species. As a supporting information we can use also easily measured morphometry – the wing length and body mass. White Wagtails are sexually dimorphic in size (males are bigger). Nonetheless, we do not rely on using just a single criterion but use combination of them. Rarely, we will encounter individuals which cannot be sexed even using information in this article, and it is best to leave these individuals undetermined.

Material & methods

Wagtails were trapped during autumns of 2019 and 2020. In total 222 individuals were trapped (154 of 1CY, euring: 3 birds). Sexing criteria were verified by molecular sexing of 66 individuals (group “known sex”; sexed molecularly using PCR and PU/P8mod primers; Pérez et al. 2011). Total number of individuals for identification of sexing criteria was 92 (group “photographed”; including 61 birds sexed molecularly).

References

Alström, P. & Mild, K. 2003. Pipits & Wagtails of Europe, Asia and North America. Christopher Helm, London.

Blasco-Zumeta, J. & Heinze, G.-M. 2020. White Wagtail (Motacilla alba). URL , accessed: 18^th February 2021

Cramp S. & K. E. L. Simmons (eds) 2020. BWP: Birds of the Western Palearctic app. NatureGuides Ltd.

Demongin, L., Lelièvre, H. & Candelin, G. 2016. Identification Guide to Birds in the Hand. Laurent Demongin, Peronnas.

Flousek, J. 2008. Konipas bílý (White Wagtail). In: Atlas migrace ptáků České republiky a Slovenska (J. Cepák, P. Klvaňa, J. Škopek, L. Schröpfer, M. Jelínek, D. Hořák, J. Formánek, & J. Zárybnický, eds), pp. 354–356. Aventinum, Prague (English summary).

Jenni, L. & Winkler, R. 2020. Moult and Ageing of European Passerines, 2^nd ed. Helm.

Meissner, W., Witkowska, M., Krupa, R. & Kleinschmidt, L. 2020. Sexual Dimorphism and Sex Determination of Juvenile White Wagtail Motacilla alba alba Linnaeus, 1758 (Aves: Motacillidae) Based on Linear Measurements. Acta Zool. Bulg. 72: 279–284. URL , accessed: 7^th April 2021

Pérez, T., Vázquez, J.F., Quirós, F. & Domínguez, A. 2011. Improving non-invasive genotyping in capercaillie (Tetrao urogallus): redesigning sexing and microsatellite primers to increase efficiency on faeces samples. Conserv. Genet. Resour. 3: 483–487. doi:10.1007/s12686-011-9385-8

Shirihai, H. & Svensson, L. 2018. Handbook of Western Palearctic Birds: Passerines. Christopher Helm Publishers Ltd.

[1] Not only because of rather frequent moult of all tail feathers, but long and soft of tail feathers are generally not in good shape when the bird is held in standard ornithological bag. This can be improved by having the birds in bags with solid bottom.