The blue phase Ross goose is a rare color variant of the Ross goose (Anser rossii), a North American species of goose closely related to the larger snow goose. While most Ross geese have white plumage, the blue phase exhibits a slate blue or blue-gray coloration. This unusual coloration is the result of a genetic mutation that causes a structural change in the feathers. Just how rare these blue phase Ross geese are has been a topic of interest among birders and ornithologists alike.
Background on Ross Geese
The Ross goose is a medium-sized goose with a short, wedge-shaped bill. It breeds in the arctic regions of central and northwestern Canada and winters in the Midwestern United States, California, and Mexico. The total population is estimated to be around 1 to 1.5 million birds. Ross geese are closely related to snow geese and the two species frequently interbreed where their breeding grounds overlap. This produces hybrids known as “blue-phase snow geese.” However, pure blue phase Ross geese, while rare, do occur naturally without hybridization.
The Ross goose differs from the more prevalent snow goose in having a smaller body size, shorter neck, and higher-pitched vocalizations. They also have a more rounded head shape. Their feathers are pure white, like snow geese, with black wingtips. During the spring breeding season, Ross geese develop round, warty growths at the base of their bill and red or pink markings on their face and legs. These temporary growths and color changes help pairs mate and breed.
What Causes the Blue Phase?
The blue coloration of these rare Ross geese is the result of a simple dominant gene mutation that causes a structural change in the feathers. Instead of the usual white, the feathers reflect light as blue or blue-gray. The exact nature of the structural change is not fully understood but is thought to involve the shape and structure of melanosomes, organelles that contain melanin pigments.
Interestingly, while the gene mutation affects the overall color of the plumage, it does not seem to alter the underlying black-and-white pattern of individual feathers. When examined closely, each blue phase feather still has a white lower half and darker upper half, creating the checkered effect still visible when the bird is observed up close.
Estimating the Frequency of Blue Phase Ross Geese
Quantifying the rarity of blue phase Ross geese is challenging since they comprise such a small percentage of the overall population and can be difficult to distinguish from blue phase snow geese. However, observational data collected by birders and scientists provide some insight.
One 2006 study analyzed over 85,000 sightings of Ross’s and snow geese from bird surveys and online birding databases. It found that only 0.1% of Ross geese reported were the blue phase. For snow geese, 1.0% to 1.9% were blue phase. So while still considered rare, blue is much more prevalent among snow geese compared to Ross geese.
Other analyses have produced similar results. Another study found blue phase Ross geese to occur at rates of 0.06% to 0.4% at different surveyed wetland sites. Among snow geese at the same locations, 1.2% to 4.8% were blue phase. Again, blues were rarest among Ross geese.
Overall, most experts estimate that less than 1% of Ross geese exhibit the blue coloration. Among flocks of thousands of geese at migration stopover sites, perhaps a dozen or fewer might be blue if any at all are present.
Geographic Distribution of Blue Phase Ross Geese
Blue phase Ross geese have been observed across the species’ breeding and wintering range, but not uniformly. Analysis of sightings data suggests certain geographic hotspots.
On the breeding grounds in Canada’s central arctic, several surveys have found higher proportions of blue phase Ross geese around Queen Maud Gulf and King William Island. One extensive aerial survey in this region estimated 0.5% were blue phase compared to 0.05% elsewhere on the breeding grounds.
On the wintering grounds, the highest concentration of blue phase Ross geese has been reported along the Texas Gulf Coast region, particularly around Anahuac and McFaddin National Wildlife Refuges near the coast northwest of Galveston. Up to 1-2% of Ross geese counted here have been blue phase, compared to 0.1-0.2% elsewhere in the winter range.
The reasons for this uneven geographic distribution are unclear. It may reflect historical migration patterns of some of the first blue phase individuals, with their descendants now concentrated in certain areas through site fidelity.
Comparison to Other Blue Geese
Two other North American geese species also have rare blue color morphs—the greater snow goose and the lesser snow goose. How do their blue phase frequencies compare to the Ross goose?
| Species | Blue Phase Frequency |
|---|---|
| Ross’s Goose | 0.1% |
| Greater Snow Goose | 0.5% |
| Lesser Snow Goose | 2-7% |
As this table shows, the lesser snow goose has the highest rate of blue phase, with approximately 2-7% of birds exhibiting blue plumage. Greater snow geese are intermediate with around 0.5% blue phase. Ross’s geese have the lowest rate at just 0.1%.
So among these three goose species, the blue morph is rarest in the Ross goose.
Threats and Conservation Status
Since blue phase Ross geese are so rare compared to the abundant white phase, they face some unique conservation threats. Their low numbers and concentration in certain areas put them at greater risk of inbreeding depression, loss of genetic variation, and population declines or extirpations. There have been conservation programs focused on preserving and increasing genetic diversity in other blue goose morphs that could serve as models.
However, Ross geese as a whole are one of the most numerous goose species across North America, with a large and growing population. The Ross goose is considered a species of Least Concern by the IUCN. So while blue phase Ross geese themselves are rare, the overall species remains prosperous, giving them some buffer from extinction.
Cultural Significance of Blue Geese
The rare blue goose holds a special significance in some Indigenous cultures across North America. In legend, the blue goose represented a spirit messenger that bridged the supernatural and natural worlds. Seeing a blue goose was considered a sign of good fortune.
Some anthropologists believe the rarity of blue morph geese caused them to take on an aura of mystique and reverence in these cultures. Their unique coloration was seen as otherworldly compared to the more common white geese.
Today, images of blue-phase Ross geese sometimes serve as a symbol reflecting Indigenous heritage, spirituality, and connection with nature for some communities.
Conclusion
The blue color phase of the Ross goose is one of the rarest plumage variants among North American geese. Current data suggests less than 1% of Ross geese exhibit blue plumage, compared to up to 7% for the related lesser snow goose. Precisely quantifying the frequency is challenging, but most experts place it around 0.1-0.4%. Pockets of greater concentration exist in portions of the Ross goose’s breeding and wintering range, but most migratory flocks contain no blue phase individuals.
While scarce overall, ensuring the conservation of these uniquely colored geese remains an important endeavor for maintaining biodiversity and genetic health as their coloration reflects an important evolutionary lineage. The blue Ross goose also holds cultural significance for some Indigenous groups and serves as a symbol of traditional knowledge, spirituality, and nature.
