Distinguishing Trumpeter and Tundra Swans

The separation of Trumpeter and Tundra Swans has been a perennial challenge. Both are obviously swans, and given decent looks they are easy to distinguish from Mute Swan, but criteria for separating Tundra Swan from Trumpeter Swan are subjective and often vague, requiring experience and/or direct comparison. Until recently there were relatively few places where the two species occurred together. It simply wasn’t much of an identification problem.

In recent years, though, the distribution of Trumpeter Swan has changed, with an active and quite successful reintroduction program establishing a breeding population in the Great Lakes region. So now the species shows up rarely in winter across the central south from Texas to Georgia , and as far northeast as Massachusetts . Birders who weren’t considering Trumpeter Swan in their identification process a few years ago now have to do so.

Recently (Dec 2005) I had the opportunity to see hundreds of both species together in the Skagit Valley of Washington, and I offer some new ideas about bill-shape field marks, and the following identification summary, based on these experiences. Comments are welcome.

This sketch shows adults of Tundra Swan on the left and Trumpeter on the right. The bill shape in profile (top), front view (middle) and top view as when the birds reach down for food (bottom). I think it’s much more useful to focus on the front and top views rather than profile views. In these views the Trumpeter’s eye is broadly connected to the black bill, whereas the Tundra’s eye appears nearly separate from the bill. The Tundra Swan illustrated is one of the approximately 10% of all adults that show no yellow on the lores. The separation of eye and bill is even more pronounced when any yellow is present. On juveniles the feathering is more extensive than on adults, and therefore this feature is more variable, but probably still useful. The V-shaped border on the forehead of Trumpeter Swan (vs U-shaped on Tundra) is useful, but can be hard to judge and some birds appear intermediate.

An excellent photo comparison of this head-on view has been posted by Mike Cooper here.

Size – Trumpeter Swan is larger than Tundra, and the difference should be obvious if the two species are together, but it can be impossible to judge in isolation. A consequence of the Trumpeters larger size is that they move more slowly and ponderously, they seem relatively short-legged and walk slowly and carefully, methodically, while Tundras seem to “prance” and move quickly and with agility.

Bill size and shape – Trumpeter has longer bill, Tundra shorter. Differences in pattern of facial skin make lores of Tundra Swan look narrower, shorter, with curved border; most birds fit this description, but there are exceptions. These differences are least obvious in profile view, and most obvious in head-on or top view. Trumpeter has dark skin connecting eyes solidly to bill, while Tundra eyes seem to stand apart from bill.

Bill color – black in adults of both species, with orange-red ‘grin’ line. Most Tundra Swans have at least a small yellow spot in front of eye, about 10% have a large yellow spot and also in about 10% this is all black, like Trumpeter, and therefore not useful for ID (it has been reported that Trumpeter can also show a pale spot, so one should not assume that this makes the bird a Tundra, but such a spot, and particularly the presence of symmetrical yellow spots on both sides of the bill, is probably so rare in Trumpeter as to be safely ignored.)

Bills of immatures are variable pink and black in both species, developing the mostly-black adult color during the first year of life. Young Trumpeter Swan always has the base of the bill and the lores black, while on Tundra Swan there is less black, the pink of the mid-bill is more extensive. In addition, the yellow spot that will appear on an adult Tundra shows up on juveniles as a blurry whitish spot, further breaking up the black lores (on the birds that show it). Also note that bills of young juveniles are oddly swollen and can appear disproportionately large – judgments of bill size are not useful on these birds.

Head shape – Trumpeter crown slope matches bill slope, then has sharp corner at rear crown; Tundra has more rounded/square head

Body shape and posture – I couldn’t see any clear difference in body stance or neck posture when standing, but Trumpeter neck base curves lower when foraging. Trumpeter tends to droop tail down slightly when feeding. No difference in wing/tail ratio: In both species the tertial tips reach the primary tips, while the tail projects well beyond the wingtips. Trumpeter Swan seems to have a longer rear body and longer tail projection beyond the wingtips, but the difference, if it exists, is simply one of degree.

Plumage – obviously, adults are all-white and plumage is not helpful for identification after the first year. The rust stains developed on the head and neck of some individual birds can occur in both species. Immatures of both species are gray-brown overall, but there are significant differences in details of the shade and extent of gray plumage, as well as the timing of molt. In early December some Tundra Swans are still in full juvenal plumage, but the majority have already molted large numbers of scapulars, creating pure white patches on the back. By mid-January virtually all Tundra Swans have acquired some white scapulars, while Trumpeters are still in full juvenal plumage.

The gray juvenal plumage of Tundra Swan is paler than the gray juvenal plumage of Trumpeter Swan. The overall pattern of color is similar, marginally darkest on the inner greater coverts and palest on the belly and rump, but on Tundra Swan the color is a pale silvery-drab, blending to white and with barely detectable color variations on feathers. On Trumpeter Swan the feathers are a darker and cleaner gray color, dark enough so that pale feather edges can be detected and often form a faint scaly pattern, and dark shaft streaks may show on some scapulars and wing coverts.

Leg color – Some juv Trumpeters have pale yellow-drab legs, unlike any Tundra, but the majority in December have dark blackish legs and cannot be distinguished by this. Also beware of dried mud coating the legs of birds foraging in agricultural fields and making them look pale.

Flight – Trumpeter has thicker neck that droops noticeably at base; Tundra has straighter neck that narrows before head. Trumpeter seems to have slightly broader wings, more rounded wingtips, slower wingbeats, and wings slightly more cupped/arched when gliding (Tundra tends to hold wings flat, but much depends on the glide angle). Juvenile Trumpeter darker gray, and some have very little white on rump (unlike Tundra) but the overall pattern is similar in the two species and Tundra can look quite contrasty gray and white.

Voice – Trumpeter Swan calls are mainly a gentle honk, like a single short toot on a trumpet, repeated; often in series of two to three notes “do-do-doo”. A series with notes on slightly different pitches may be given by birds in chorus?? Juveniles call like adults

Tundra Swan calls are varied bugling, higher than Trumpeter calls, crane-like clucking rattles. Juveniles occasionally give high whistled squeal

Wings of both species make loud creaking sound on takeoff, like Mute Swan but without the humming overtones. The sound produced by Tundra Swan may be slightly quieter (and in more rapid pulses because of quicker wingbeats)

References

A good summary of differences is provided by the Trumpeter Swan Society here.

Serious efforts to work out the identification of individual birds in California are posted by Joe Morlan here .

Kevin McGowan shows a page of photos and discussion from a NY perspective here.

Some interesting photos and comparisons from Colorado are provided by Bill Schmoker here.

Thanks to Steve Mlodinov and Malcolm Frasier for help in WA. And to Martha Jordan and the Trumpeter Swan Society for comments.