Separating Ross's and Snow Geese (so-called
“white” geese in the Genus Chen) can sometimes cause problems
for those who aren't used to seeing these two beauties! Both of these
geese are high arctic breeders with booming populations. They migrate
throughout the United States and winter in the southern regions of the
country, sometimes delighting our friends across the pond as vagrants
to Europe. Away from the US Southwest and Gulf Coast wintering
strongholds of Ross’s Geese we find flocks of primarily Snow Geese
with the occasional Ross's mixed in, growing rarer to the east.
Part of the
challenge with Chen geese is their variability. Snow Geese are the larger of the sister species but note that there are lesser Snow Geese that approach the diminutive Ross's in size. Both of these species come in light and dark morphs known as “Blue Geese”, although dark Ross’s Geese are exceedingly rare. Some Blue Geese are "bluer" than others (they have more extensive dark feathering on their bodies) and juvenile Blues can look nearly all black while juvenile light-morph birds look dirty light gray. With the variability in coloration it becomes important to focus primarily on size and structure to separate these birds.
When seen together, separation of the
two can be fairly self-explanatory. Notice the four birds in the photo
above. Can you see the size and shape differences here? There
are two Snow Geese (one a dark-morph) and two Ross’s Geese in this
photo! The Ross's Geese (top and second from the bottom) are smaller
versions of the Snow Geese, sporting much stubbier bills with little
or no "grin patch" and a shorter neck. The culmen (top of
bill) is nearly straight on the Ross’s Geese while the Snow Geese
display gently dished culmens. Ross’s heads look more rounded,
and between that and the shorter bill one might call them "cuter."
Not as cute are the bluish warty bumps (caruncles) that mature male
Ross’s develop at the base of their bill. Snow Geese have a much
larger bill with a noticeable dark grin patch (combed black where the
upper and lower halves of the bill meet (above and below the tomia,
or inner cutting edges of the bill), a flatter looking head, and a proportionately
longer neck. If you can see black in the center of the bill from any
distance, particularly from afar, then you are looking at a Snow Goose.
Two more comparison pics follow, the first of a Ross’s Goose and the
second of a Snow Goose.
Even at a distance, note the structural
differences between the Ross’s Goose (trailing) and the Snow Goose
(leading) in the following picture:
Sometimes problematic birds show up that don't quite fit either species very nicely. Hybrid Ross's x Snow Geese blend traits of each, typically showing small grin patches along with intermediate-length bills and necks. We suspect the birds below are hybrids because the bills look a bit longish and they have a little more grin patch than ideal for slam-dunker Ross's.
The above shot was taken at Bosque Del
Apache National Wildlife Refuge last November. While the Sandhill Cranes
get a lot of the spotlight at Bosque
del Apache, the geese also
provide spectacular sights, comparison studies, and photo opportunities
at the refuge. In a welcome turn from the hordes of sky carp found in
much of the US, white-cheeked geese (Canada & Cackling) are kind
of scarce there. But so-called "white" geese are present in
force and typically show well. For some reason, the Farm Loop on the
refuge didn't have corn planted last year so the goose situation had
changed from previous years. It was tough to get the massive "blast off" shots that happened on the northern part of the refuge
when a coyote or eagle spooked 4
or 5-digit goose flocks,
but there were still plenty of chances to study and photograph almost
all of the Chen flavors (still haven't seen the elusive dark-morph Ross's Goose...)
Here are examples above and below of Snow Geese showing the contrasting blue phase. Notice the prominent black grin patches?
In the above photo we have an adult Snow Goose in the foreground with two Ross's Geese off to the right and back. Note the bluish warty base of the bill of the nearer Ross’s Goose. While Ross's Geese are the smallest in the bunch, judging size on a lone bird can be a dangerous task, and about any white goose looks small amongst large races of Canada Geese. Beyond the presence or absence of a grin patch let's focus on structural attributes such as the head shape and bill size. Ross's Goose has a short stubby neck and rounded head (the domed profile due to the steeper forehead) to accompany the smaller, stubbier bill. In contrast, focus on the proportionately longer neck and shallow slanted forehead of the Snow Goose leading to a slightly dished culmen (see also another Snow Goose photo below). These traits can be seen in flight with some practice, even when scanning large flocks of multiple hundreds or thousands of white geese. It always helps to have superior field-of-view to sort through flocks of these arctic winterers such as the panorama found in the Nikon EDG 7x42 binocular. These bins display 417 feet at 1000 yards which is top of the class for this specification.
This photo of an adult Ross's Goose below shows us the substantial size differential with the Canada Geese in the background. Another topic altogether is variation in Canada and Cackling Geese, but Ross’s are the smallest of the lot. Be aware that Snow Geese can overlap in size with the smallest forms of white-cheeked geese, re-emphasizing the need to use structural cues, not just size, to identify lone chen geese mixed in with white-cheeked geese.
This final shot of a Ross's Goose summarizes the shorter neck, domed head shape, lack of black grin patch and bluish caruncles at the base of the stubby bill!
Photos by Bill Schmoker using a Nikon D300 and a Nikkor 200-400mm f/4 G-AFS VR lens for his photography. Good birding!
Check out more postings by Mike at Birding to the EDG and Bill at his blog
Also see Nikon Birding's You Tube Channel