The Grey Wagtail can be confused with the Western Yellow Wagtail. The latter also has the lower parts of the belly yellow in color, but unlike the Grey Wagtail, it has dark-colored legs and a yellow-green back.
As for the White Wagtail, it is not possible to confuse it with the cascade.
Adult males and some second-year males have a black throat during the breeding season, although some individuals occasionally have this area speckled with white. Generally, the forehead and crown are gray with some feathers ending in a diffuse green color. The lower parts of the belly are a bright yellow color. Second-year males have a white speckling on the throat, similar to the case of the adult female.
On the other hand, the adult female typically has a white throat, occasionally with black speckling. The lower part of the belly is a duller color than the male. The throat of the second-year female is usually white, although there are specimens of these characteristics that can have a black throat similar to that of adult males. During winter, males, although with much duller plumage than during the breeding season, continue to differ from females by the slightly more yellow belly, although there is a great overlap between the two sexes.
NOTE: it is a species with a spectrum too wide to sex using only the design of the plumage, so it is recommended to observe other variables.
It is possible to recognize 4 different ages:
Juvenile specimen: they have a new plumage. No generational change of molt. The eyebrow is quite smaller than in other ages and the tips of the large secondary coverts are white.
1st-year specimen: the molt limit is marked between the changed greater coverts and the un-molted ones (which can be seen clearer due to wear). In the case of no greater coverts having molted, the limit can be observed in the lesser or median coverts. In the case of all the greater coverts having molted, the molt limit can be between the tertials, primary coverts, or rectrices. Primaries and secondaries are maintained from the previous generation (juvenile), so they show visible wear.
2st-year specimen: these individuals are distinguishable in those cases where the post-juvenile molt is still apparent, having three different generations of feathers.
Adult specimen: in the autumn months they retain all the wing feathers of the same generation. A different case in spring, after the pre-nuptial molt, they have two generations of feathers, but one must be careful as it is not always possible to date the age based on the plumage at these times as specimens with two generations of feathers in the wing could be adult or 2st-year.
Grey Wagtails perform a complete post-nuptial molt that usually ends at the end of September. On the other hand, the post-juvenile molt is partial. This process includes the body feathers and lesser and median coverts. In some cases, specimens that have not molted any feathers from the primary coverts can be observed.
Primaries: 10 per wing.
Secundaries: 9 per wing.