Peacock

Peacock
Peacock

Wednesday, January 11, 2012

Those Frustrating Blue and White Geese

When the refuge does its bimonthly survey of geese and ducks, it has to list the geese as white, white-fronted, Tule, Canadas and Cackling - in several subspecies.

But actually the white geese are made up of two species, Snow and Ross's and two morphs - a blue and a white - in both. They hang out together or separately but when you are measuring white areas and translating that into geese, the species can't be differentiated.

The last survey in December, 2011 showed that there were 57,000 white geese on the refuge. Even though I know snow geese well, I have never gotten comfortable in identifying a Ross's goose because, in the central flyway, Ross's are extremely uncommon and I'm a very slow learner.

But in Sacramento Valley they are estimated to make up thirty percent of the white geese, and they can be found on any given day in in most groups of white geese, sometimes in large, pure groups. So I've started learning the differences between snows and Ross's geese.

I still can't see the faster wing beat of the Ross's geese and the smaller body when they are flying, but I can spot them on the ground pretty easily now.  The Ross's have a cuter, baby-faced  look to them because their heads are rounder and their bills are shorter, as compared to each other and as the bill length is compared to the thickness of the bird's neck just at the junction with the head.

This picture has three Ross's geese in it. See how the bill is really short and the head round?  And see how small they are- hardly bigger than a pintail duck. 



These geese all look like snows.  See the longer bill and more elongated head? See how the bill is longer than the diameter of the neck?




I can't see these next birds well enough to tell what they are for sure, but think they are all snows.  All the birds with grey backs are this year's young. Some visitors see them as a different species.  I think they are now leaving their family groups and hanging out with their friends.  Usually I see two adults with two or three young but yesterday I saw about twelve young birds with brownish heads and varying amounts of grey in their backs hanging out together.

 


Blue morphs occur in both species. I'm used to seeing about twenty-five to thirty percent of blue morphs in the central flyway, but here they are very rare.  I took all the pictures of  blue morphs in one day and haven't seen any since then. But a visitor showed me a picture he had taken of a blue Ross's goose. Blue and white are color genes and blue is an in incomplete dominant gene.  (This really surprised me because the ratios made me think blue was the recessive gene.)  However blue geese prefer to mate with each other and white geese also prefer each other.  But geese often lay eggs in other geese's  nests so sometimes a blue is raised by a white pair or a white goose is raised by a blue pair.  These geese imprint on their parents and mate geese the color of their parents. If a goose is a hybrid of the two colors, it will have a white belly.  That means one parent was white and the other was a blue.

The dark goose in this picture had one white parent and one blue parent. The blue and the snow in the foreground are showing another snow feature, the snow grin patch and strongly curved lower mandible. Both of these are absent in snows. The grin patch looks like a black marking on the bill.



Another blue snow goose, this time with a mix of snows and Ross's. At least four of these geese are Ross's. And the snows show the bill markings clearly.




This is yet another blue.  I know because I photographed them all in the same half hour and just moved from one resting group to another. I think a couple of the geese way in the back are Ross's but I need a more sideways look to be sure.




A month after I got the blue snow geese, I was able to get a barely adequate picture of a blue Ross goose. I found it while checking out the auto tour - this mostly means looking at birds but we also note any drivers out of their cars and ask them to get back in. I found this bird about 30 minutes before I had to be back to turn in my vehicle.  And he would NOT wake up and pose for me. Finally,  I rushed to headquarters, turned in the car and hurried to my car.  Then I had to go around at least thirty cars before I could get back to the far end of the auto tour.  By this time the bird had woken up and moved further back in the crowd. But this picture is very exciting to me anyway, as this is my first blue Ross. And since there are only about one blue Ross's to every 10,000 white Ross's, if I get another picture this year, it will probably be of this bird.




And to make matters even more confusing, these two breeds can hybridize.  In fact, some experts believe that blue Ross's geese are actually hybrids between blue snows and Ross's.  If that is the case the blue gene doesn't work the same way AND their bills don'tlook like those of hybrid snows/Ross's.  I'm sure I'll never notice any hybrids, though. For a thorough discussion of how to identify these two species and the hybrids of them, along with drawings, see David Sibley's blog on Identification of White Geese. Thankfully, I pretty much don't have to think about the greater snow geese that occur in the Atlantic flyway.