Anas platyrhynchos

Mallard / Gräsand

Main author:
Stina Andersson, July 2014.
Supplemented by:
Magnus Hellström, July 2014.
Daniel Bengtsson, February 2016.

Citation: 
Ottenby Bird Observatory. 2015. Ringers' DigiGuide - Anas platyrhyncos. www.ringersdigiguide.ottenby.se
Also see publication in Ornis Svecica: 
Age and sex determination of mallards (Anas platyrhynchos) in autumn. 2016.
 
MOULT:
                      Adult          Young
summer        
SC               sp
winter            wp               wp
Young sp: The post-juvenile moult (c. July-September) includes parts of body, e.g. breast, flank, parts of mantle, scapulars and head.

Young wp: The pre-breeding moult (c. August-November, but often prolonged during winter/early spring) starts shortly after completing the post-juvenile moult. Includes most of body parts, scapulars, tertials, tertial coverts and tail. The extent and timing of the moult is much depending on the date of hatching. Females usually retain some juvenile tertials and tertial coverts until the following spring, whereas most males have moulted all tertials by late November (probably due to sexual selecton).

Adult SC: The post-breeding moult (c. May-September) includes the complete plumage. Flightless for c. four weeks in mid-summer while moulting primaries.

Adult wp: The pre-breeding moult (c. August-November, but often prolonged during winter/early spring) starts shortly after completing the post-breeding moult. Includes various parts of body, scapulars, tertials, tertial coverts and tail.
AGE:

Juvenile tertials and rectrices are the most easily detectable characters for ageing both sexes of mallards. All other criteria are subject to large variation, and should not be used other than as supportive criteria. Mallards with only post-juvenile TT and RR may need to be left unaged, if not showing typically juvenile criteria in other features. Judging age of mallards by single characters is often impossible, especially from photos, and some individuals may even be challenging with all characters presented.

Autumn males
Autumn females
SEX:

Young mallards are generally possible to sex by field characters already before they have become independent from their mother. Females have an orange bill with a variable blackish pattern often covering a large part of the upper mandible. In the typical case, the dark area starts close to the base of the bill (often leaving a narrow, clean orange area next to the feathering), covers the nostrils and reaches to about one centimeter from the blackish bill tip. Adult (i.e. 2cy+) females acquire more distinct blackish pattern and sometimes extensive blackish spotting. The young males soon develop a greenish-yellow bill, which often appear plain with a (less extensive) dark area on the central upper ridge. Adult birds are always easy to sex according to bill patterns, although genetically depleted feral birds (and perhaps other?) may deviate from the normal patterns. Males in eclipse plumage may appear superficially similar to females but differentiate from females by blacker crown and more greyish face and neck.
 
After the post-juvenile moult, sexes are easily separated by plumage differences. The green head, white necklace, brown breast, grey body and black rear of males make them very beautiful. The females take full care of eggs and ducklings and, therefore, need to be camouflaged. Their plumage has buff and tawny-brown ground colours, heavily marked with various black patterns. The wing pattern is, however, quite similar between the sexes, especially in 1cy birds. In general, females have browner wing coverts, some with obvious buffish edging (rare in young males, absent in adult males). The black tips to greater coverts are on average broader in males, but the white wingbar on greater coverts is longer in females and reaches the tertial coverts, whereas it barely continues beyond the secondaries in males. Only males attain grey and vermiculated scapulars, and innermost underwing coverts are broadly barred in females, but finely vermiculated in males.
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