Date of this Version
Johnsgard, "What Are Blue Ross's Geese?" from Nebraska Bird Review (June 2014) 82(2).
The existence of blue morph ("phase") Ross's Geese (Chen rossii) was first well documented by McLandress & McLandress (1979). They reported on several blue-morph birds seen and collected in California and Canada that morphologically appeared to be pure Ross's Geese and on others with intermediate traits that appeared to be hybrids with Lesser Snow Geese (Chen caerulescens caerulescens). They also noted that in the California wintering grounds counts held during 1976–77 there were only 3 blue morphs (0.008 percent) among the 38,825 Ross's Geese counted. At that time, only 0.02 percent of the Lesser Snow Geese wintering in California were blue morph, but sightings of blue-morph geese from central Canada were by then already slowly increasing in frequency (Dzubin 1979). Blue-morph Lesser Snow Geese currently represent about 25 percent of the Central Flyway flock of several million Lesser Snow Geese (Johnsgard 2012).
At the same time, Ross's Geese have expanded their breeding range eastwardly across Hudson Bay, and now probably comprise at least two percent of the mixed Snow/Ross's Goose flocks that migrate through Nebraska (Johnsgard 2012). Assuming that about 4.6 million Snow Geese were in the mid-continent flock during the 2013 winter surveys (U.S. Fish & Wildlife Service 2013), there might be at least 90,000 Ross's Geese in the Central Flyway, and there may be far more. In the west-central population of 725,000 "light geese" that passes through the high plains, nearly a third counted during the 2013 winter survey were Ross' s Geese.