What's the easiest way to tell the difference between a black duck and a hen mallard? - Martin Barlow
How do you tell a female black duck from a male black duck? - Philip Mcqueen
Martin and Philip,
Although a Black Duck and Mallard are identical in size, there are several main differences between the Black Duck and hen Mallard. First of all, the Black Duck is much darker than a hen Mallard. The Black Duck has a very dark body, with a noticeably lighter colored brown head. The hen Mallard is a much lighter brown with the same color body and head.
In hand, Mallards and Black Ducks can be distinguished by simply looking at their wings. The speculum (bluish purple patch on wing) of a Mallard is bordered by white, while the Black Duck speculum is not.
To distinguish between a drake and hen Black Duck, you need to look at the bill. The drake Black Duck has a yellow to greenish yellow bill with no blotches, while the hen Black Duck has a greenish olive bill with blotches.
To tell the difference between an immature drake Mallard and a hen Mallard (in hand), there are two main techniques available. On a hen Mallard, the top white stripe (leading edge) bordering the speculum extends past the speculum in to the wing, while the leading edge on a drake Mallard stops at the edge of the speculum. The other technique available is bill color. Just like the Black Duck, the drake has a yellow to greenish yellow bill with no blotches, while the hen has a greenish olive bill with blotches.
Thanks for the great questions!
Joel Brice
Photos courtesy of the Central Flyway Waterfowl Council publication “Waterfowl Identification in the Central Flyway”
(http://www.npwrc.usgs.gov/resource/tools/waterfwl/waterfwl.htm#contents)