蓝雪雁




http://en.wikipedia.org/wiki/Snow_goose
ZT:
The snow goose has two color plumage morphs, white (snow) or gray/blue (blue), thus the common description as "snows" and "blues." White-morph birds are
white except for black wing tips, but blue-morph geese have bluish-grey plumage replacing the white except on the head, neck and tail tip. The immature blue
phase is drab or slate-gray with little to no white on the head, neck, or belly. Both snow and blue phases have rose-red feet and legs, and pink bills with black
tomia ("cutting edges"), giving them a black "grin patch." The colors are not as bright on the feet, legs, and bill of immature birds. The head can be stained
rusty-brown from minerals in the soil where they feed. They are very vocal and can often be heard from more than a mile away.

White- and blue-morph birds interbreed and the offspring may be of either morph. These two colors of geese were once thought to be separate species; since
they interbreed and are found together throughout their ranges, they are now considered two color phases of the same species. The color phases are
genetically controlled. The dark phase results from a single dominant gene and the white phase is homozygous recessive. When choosing a mate, young birds
will most often select a mate that resembles their parents' coloring. If the birds were hatched into a mixed pair, they will mate with either color phase.