Are You My Mother? (merganser edition)

On a recent trip to Huntley Meadows, Victor & I got to see something that not only checked off one of my target species, but was somewhat puzzling. We were on the boardwalk lookout tower when I spotted a Canada Goose swimming along with a group of smaller birds trailing it. “Oh look, goslings!” I said, before I got a good look at the birds. In fact, it was a group of Hooded Mergansers following the goose as if they thought they were indeed goslings themselves. How funny!

Huntley Meadows is an unusual breeding spot for Hooded Mergansers, who normally breed much further north. They've been here for several years now, though, and seem pretty settled in.

I initially thought the appearance of family relations must have been only coincidental, something I imagined or added to the scene without a real basis in actuality. But when I was looking for more information on the algal bloom we also observed there (link here), I found photos of a Canada Goose apparently acting as nanny to a family of Hooded Mergansers both this year and last year, posted on the Huntley Meadows Community Facebook group.

My ornithologist friends suggested a few theories for what’s going on. Hooded mergansers are known for brood parasitism, where the mother bird lays her eggs in someone else’s nest, leaving that nest’s mom to raise her chicks. However, the difference in size between mergansers and Canada Geese makes this seem somewhat unlikely. When I looked closer at my photographs I also realized that the mother merganser was accompanying the juveniles and the Canada Goose, so she didn’t totally abandon her clutch. Another possibility is that the mergansers somehow imprinted on the Canada Goose. This is my favorite so far. I wonder even if the mama merganser herself imprinted on the Canada Goose, when she was young, and now has taught her own babies to do the same.

The mother is at the back of the group in this shot, slightly larger than the juveniles.

Either way, however, I still wonder what the Canada Goose thinks about it! What do you think might have led to this odd partnership? Feel free to suggest more theories in the comments.