Mallard Stretching Behavior
I watch Mallard ducks often and have noticed them doing a very
strange activity. It's often late in the afternoon and a group of twenty
plus are swimming together. All of a sudden, either a single duck or up
to a dozen will do a stretch like move and make a sharp whistle noise.
After, all the ducks in the group lower their heads and start quickly
swimming around. It's almost like they are playing a game of tag.
Everyone in my office thinks I'm crazy because I seem to be the only one
who sees it. Do you know what they are up to?
This is a common competition and courtship behavior sequence. Very similar
behavior is common to other related species of ducks. Mallards do a lot of
this in the fall, when most pair bonds are formed, and it may occur again
in spring when there is new competition and to reinforce bonds. See Stokes
Guide to Bird Behavior, Voume 1, for much more fascinating information.
Based on your description, this sounds like mating behavior. The breeding
season for most ducks is quite long (ever notice that male Mallards molt out of
colorful breeding plumage only during mid-summer, then right back into breeding
plumage in fall?). So in autumn, ducks are starting to pair up again,
continuing through winter in moderate climates. Ducks in general (mallards,
pintails, teals, ruddy ducks, mergansers, etc.) engage in a variety of head
motions (nods, flips, lunges, shaking, etc.) during mating behavior, so I'm
sure this is what you're seeing. Also, male mallards (and some other ducks)
are known for whistling during this display. The mating displays of mallards
(in contrast to, say, many grebes) can be quite brief, separated by minutes of
calm, so you're a keen observer.
The "tag" you describe I'm not certain about, since you didn't indicate gender.
Males playing "tag" with each other may be showing territorial-breeding type
behavior. Unmated males often aggressively try to weaken and forcefully mate
with (usually) unmated females, which could look like "tag".
I recommend "Stokes Guide to Bird Behavior, Volume 1" for more detail (this
volume includes the Mallard). You can further amaze your friends by explaining
that drake (i.e., male) Mallards don't "quack". The loud "quack" you hear is
the female. The male's call is usually described as a soft nasal "rhaeb" sound
(or the whistles you heard).
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Update: June 2012