The anomalous goose – another hybrid?

20170220_122723There are a range of species of geese around the university lakes, and I’m pretty familiar with all of them. So it’s always a surprise when one appears that I have to look twice at.Such was the case on Monday, when in amongst some foraging Greylag was this goose.

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At first glance it’s quite Greylag-like. But that white stripe round the belly and flanks is not normal, nor is the white between the bill and the head. You can see it alongside a ‘normal’ Greylag here.

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So what are we looking at here?

One option is it’s a morphological colour variation. This means a different colour pattern to the standard bird. We see this in many species, for examples common buzzards which can vary from very pale to very dark.

There are also conditions that strip out or add pigments, such as leucism, albinism, and melanism. But they would usually affect the whole bird.

The third option is this is a hybrid. Now, I’ve featured some very clear hybrid geese here before, for example this Canada Goose x Greylag Goose. So could this be another case?

Well, on site we have Canada Geese, Barnacle Geese, and Snow Geese. All of which can hybridise. But this doesn’t look like any of the recorded hybrids I can see online. But it could be a Greylag x Snow. It looks like what is described as a Greylag x Swan Goose, but I don’t know where that genetic mix would happen here. Possibly a domesticated goose.

The white patch on the head above the bill makes it look a bit like a White-Fronted Goose, but there are none around here and that wouldn’t necessarily explain the white belly, unless it was a White-fronted crossed with, say, Canada Goose. But I would expect some of that Canada Goose patterning in the head. I’d also expect it to be hanging around with the Canadas. This identifies itself as Greylag.

So it’s a mystery for now, and I welcome any suggestions. My personal feeling is it’s either a bird showing partial leucism, or it’s got some degree of domestic ancestry. What do you think?

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I welcome thoughts, comments and questions, so please feel free to share anything at all. Thanks, David

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