Thursday, 16 October 2014

juvenile Ross's x Snow Goose - North Bay

A few days ago a Ross's Goose was posted to Ontbirds, having been seen for several days on some sports fields near the waterfront of North Bay. As I was planning on doing some work near North Bay today, I stopped in on my way home to look for the goose.

As I approached the fields along a nearby road I could see a small white goose in with the Canada's - that was easy! Unfortunately the heavy rain meant that I was going to get wet trying to photograph the bird, and I still had a 4 hour drive ahead of me, so I wanted it to be quick!

The birds were easily approached - probably due to the high pedestrian traffic this area must receive. With a little bit of patience I was able to approach within 20 feet of the white goose, as it busily fed on grass. Most of the time, my views of the bird were like this - head buried deep in the grass.

presumed Ross's X Snow Goose - North Bay, ON

As I was photographing the bird it became apparent that it might be a hybrid, as its bill shape in particular was not quite right for Ross's Goose.

presumed Ross's X Snow Goose - North Bay, ON

Ross's Geese have a very short, triangular bill, while the closely related Snow Goose has a much larger bill with a distinctive black oval on its lower half - referred to as a grin patch. Here is a photo of a Snow Goose, showing the grin patch. Note that bill colour is quite variable in both these species and is also dependent on the time of year, age of the bird, etc.

Snow Goose - Guelph, ON

I don't have any decent photos of Ross's Geese yet, but here is one I found on Wikipedia Commons. This bird has a relatively large bill for a Ross's Goose.



David Sibley put together a cool little sketch showing the differences in head and bill shape of Snow Geese, Ross's Geese, and presumed hybrids - check it out (along with the full article on how to tell them apart) at his blog.

Pure-blooded Ross's Geese should show a straight (or very slightly curved) border to the posterior edge of the bill (where it meets the face). Pure Snow Geese on the other hand always show a curved border. The North Bay bird shows traits someone intermediary. It is noticeably curved, but not as much as a Snow Goose.

presumed Ross's X Snow Goose - North Bay, ON 

With these two species, there isn't necessarily a clear line between what is a Snow Goose and what is a Ross's Goose. These species have a relatively recent common ancestor and as such, not much evolutionary time has elapsed. At this point in time they can still have viable hybrid offspring, and those in turn can reproduce with a "pure" individual of one species to produce a backcross. There likely is a fluid spectrum of birds that can have any percentage of hybrid ancestry, especially in the areas where the two species' ranges overlap.

presumed Ross's X Snow Goose - North Bay, ON

Despite the heavy rain it was an interesting study of a neat little goose, and a great birding side trip after a long day of work!

5 comments:

  1. Very interesting post. Thanks.

    Here is a photo I took of a Ross's in Halifax in Jan 2013. Yours definitely seems to have a longer bill and shows more curving at the face.

    https://flic.kr/p/fMjA2U

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  2. We had an interesting similar situation a few years ago in Michigan

    http://intothewoodsandelsewhere.blogspot.com/2011/03/dearborns-first-rosss-goose-1847-26353.html

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  3. Thanks for having a closer look at this bird. Quite interesting. I took some photos and sent them to Martin Parker and Steven O'Donnell and they thought it was a Ross's. I didn't try to get closer to the bird for fear of scaring it away. Even with 15X optical zoom, they were not good enough to show the subtle features that would indicate it was a hybrid. What made me personally decide it was a Ross's was the light shading on its back that an immature Snow Goose would not have. Everything else was frustratingly indistinct. Now I know why. It also makes sense why my mother in law and Cal and Sandra were all having difficulty with it.

    I feel a little guilty that I waited so long to post it on OntBirds. I presume it was first seen on October 4th during our monthly bird bash as Dick Tafel left me a message on the answering machine about it. However, I did want to be sure of the id before I posted it, with photographs and all. Martin Parker asked me to post it on OntBird and I was glad I did.

    Despite this bird being a hybrid, I am going to keep the Ross's Goose on my life list, with a side note of course. I only other hybrid I have seen has been a Mallard X Black Duck.

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  4. I've heard back from several people regarding the ID of this goose. Most who have emailed me agree that it looks like it could be of hybrid origin. Apparently it looks very similar to the Ottawa bird from the OFO conference in late September, which was also determined to be a hybrid. I haven't seen photos of it and I don't know who determined it was a hybrid, but if someone has photos of that bird I would be interested in seeing them.

    A few other people think that the North Bay bird is a pure Ross's Goose. Apparently some young birds will adopt a bill shape that is a little wonky and can make it appear hybrid-y. This is something I was unaware of. Googling images of juvenile Ross's Geese, some have a fairly "traditional" bill shape while others look more similar to the North Bay bird.

    At any rate, to my eyes at least the bird shows features intermediate between what I would expect for ROGO and SNGO. This may be normal variation within ROGO, or perhaps it is something that can be seen in both pure ROGO and hybrids when they are young. If it's impossible to tell apart a hybrid from a pure individual, there is of course the argument of what those birds should be labeled as. I think that in a situation like this, birders usually take the route of assuming the bird is pure unless there is some other reason to assume hybrid).

    At any rate, this bird could still very well be a pure Ross's Goose! Overall its color looks good for Ross's (Snows are usually a lot dingier) and it's size seemed about right as well.

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    1. Thanks for several people who passed along the photos of the Ottawa bird which was determined to be a hybrid. It looks quite similar to this one in most aspects. It's bill is slightly longer, but the body colour, dark eye line, size of grin patch, and shape of the posterior border of the bill looks much like the North Bay bird. The Ottawa bird looks similar in size too, though this is not always easy to judge from one or two photos.

      An interesting bird regardless...

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