Identification of these two swans can be tricky, especially for persons
unfamiliar with one or both of the species. Characteristics often overlap or
are subtle; even diagnostic characters can be difficult until experience is
gained observing both species.

When perusing flocks of swans for trumpeters, I generally look at the eye. In
most tundra swans the eye is readily distinguishable from the the black leathery
extension of the bill (which meets the eye in a narrow point). This is further
enhanced on the tundras that have the characteristic yellow spot. On trumpeter
swans, the bill extension envelops the eye. If you were to look at the swan in
a one-dimensional flat black and white context, the trumpeter swan eye would be
barely discernible from the bill extension, if at all. In the tundra swan, the
eye would appear as a large button, nearly separate from the bill extension.
This works well even at a distance and will separate out most tundra swans
quickly (but not all). From here, other standard trumpeter identification
features need to be looked at and/or compared with obvious tundras. These
other morphological or behavioral features (such as bill "V" notch, bill slope,
neck kink, body size and posture) are too detailed to explain here.

Tundra swans tend to hold there head (bill) on a horizontal plane with the neck
held vertical. Trumpeters tend to have the bill pointed downward at a slight
angle (for feeding or semi-alert birds only) and their necks are often curved or
bowed to some degree. While alert, tundras tend to nod their head or have a
quick stiff neck bob returning the bill to horizontal and neck to vertical.
Trumpeters exhibit a deeper head/neck bob resulting in a 'S' curved appearance
to the head/neck, not the angular profile of the tundra. These differences fall
apart quickly depending on the alertness of the trumpeter.

Other trumpeter clues include: small flocks or family groups separate or on the
periphery of a large flock of swans; trumpeters are generally dominant in a
mixed flock, thus tundras tend to give way when a trumpeter approaches; tundras
prefer more open sites while trumpeters will use areas with enclosed vegetation
or more visual barriers. By mid-winter, most immature tundras have attained
their white plumage with only a scattering of light gray feathers remaining.
Trumpeter immatures can remain quite gray into the spring and are
near-diagnostic this time of year. Again all of these are clues of possible
trumpeters and are not diagnostic. They are based on observations of swans in
wetland situations and may not hold true for field-feeding birds such as in
Skagit County.

The Trumpeter Swan Society has published an identification pamphlet for
distinguishing the two swan species. I published an article in UTAH BIRDS,
Volume 6, Number 1, March 1990 that attempted to explain some of the subtle and
distinguishing characteristics of the two swan species. While it needs some
improvement, it may be useful. Unfortunately, I do not have either of these in
a readily available electronic format but will send paper copies to interested
persons if they email an address to me.

Joe Engler
US Fish and Wildlife Service
Ridgefield, WA
joe_engler at mail.fws.gov