Order: Anseriformes.
Family: Anatidae.
Male with unmistakable plumage. Both sexes lack epaulets which makes them easily distinguishable from the rest of ducks.
The male of Gadwall in breeding plumage is unmistakable. It presents: its body feathers are gray, a dark-colored beak, gray-streaked flanks, median-brown secondary coverts, vermiculated scapulars, black undertail coverts. On the other hand, with eclipse plumage the male resembles the female much more, but the orange bill loses the black spots and a wide brown patch on the median secondary coverts, brown spots on the upper scapulars, and flanks with “V” shaped marks (ATTENTION: possible individual variation); white undertail coverts with irregular spotting.
The female presents: brown color, generally orange beak with black spots, ochre flanks with brown spotting in a “U” shape (ATTENTION: possible individual variation), median wing coverts only slightly tinted with brown color, never vermiculated scapulars, with “U” shaped marks (ATTENTION: possible individual variation), undertail coverts of dark spotted brown color.
It is possible to recognize 2 different ages:
1st year/2nd year especimen: with adult appearance but retains worn feathers on the wing and tail. Male with reddish color only in part of the median secondary coverts, lesser coverts not vermiculated, with some light bands and light edge, greater coverts black. 5th to 7th with clear tip and wide edge, sometimes with a little black or black tip on the outer beard. Female with lesser coverts always with a cream band, greater coverts dark. 5th to 7th with clear tip and wide edge, without black or black tip on the outer beard.
Adult especimen: with little worn flight and tail feathers. Male in breeding and eclipse plumage with many median and lesser coverts of reddish color close to the wing edge finely vermiculated, sometimes light gray without pattern. 5th to 7th with much black or black tip on the outer beard and without white edge, outer beard of the greater inner coverts intense black without light edge. Female with median coverts with a light edge and only a few reddish ones, lesser coverts always with a light edge and never vermiculated, greater dark coverts always exceeding the width of the white epaulet. 5th to 7th with white tip and little or no black or black tip on the outer beard, outer beard of the undertail coverts black, sometimes with a narrow white edge.
Gadwall undergo a complete post-breeding molt, acquiring eclipse plumage. This process usually ends in July (males) or August (females). The post-juvenile molt is partial, changing body feathers and sometimes tail feathers, usually ending in October. Both age classes, from September, have a partial pre-breeding molt, changing body feathers to acquire breeding plumage.
Primaries: 10 per wing.
Secundaries: 16-18 per wing.
Rectrices: 16-18.
