Friday, April 14, 2006

Goose Step and Fox Trot

Our shoreline was particularly busy during one evening last week. A pair of Wood Ducks (Aix sponsa) and a male Ring-necked Duck (Aythya collaris) gorged on cracked corn near the water's edge. Small courting parties of Bufflehead (Bucephala albeola) and Hooded Merganser (Lophodytes cucullatus) squabbled and paraded in the thawed margins of the bay.

The highly animated sights and sounds of courting Hooded Mergansers are not easily forgotten. Dugger et al. (1994) gave this account:

Head-throws, the most elaborate display, are usually performed with the male parallel to the intended female. With crest raised, males bring their head abruptly backward touching their back. A rolling frog-like crraaa-crrrooooo call is given as the head is returned to the upright position and turned away from the intended female.

More extraordinary was the drama that unfolded between a Red Fox, (Vulpes vulpes) and the resident pair of Canada Geese (Branta canadensis). Late in the afternoon a bedraggled fox coursed across our lot and stopped to glean small bits of suet that had fallen to the ground beneath our bird feeders. Soon, its attention was drawn to a pair of Canada Geese resting on the shoreline. And that is when things got more interesting.

But first, here's a little background on the responses of the local waterfowl to the approaches of (bipedal) mammals. Typically, when we walk down to the waterfront, the ducks and geese disperse. Buffleheads and Mergansers skitter into flight and disappear for an hour or more. The Wood Ducks also take flight, squealing as they wheel back into the wetland. The geese and Mallards generally swim out from shore and return soon after we've left.
Canada Geese repelling Red Fox. Photos by Martha.
On this day, with this potential threat, the geese responded very differently. Instead of swimming to immediate safety, the geese stepped up on shore and approached the fox while honking and hissing, standing in single file (see photo). The fox feinted to one side, and then the other, but these moves did not expose a vulnerable flank. Instead, the geese honked more loudly and the lead goose spread its wings while continuing to approach the predator. The second goose, standing directly behind its mate, remained in lock step.

This was all too much for the fox. It broke off the engagement and headed east, likely in search of easier fare.

Why did the geese make such a grand stand, and put so much energy into routing the fox, when they might have simply swam out of harm's way?

In an evolutionary sense, fox and geese are no strangers. In the Canadian arctic, where the ecology of nesting geese has been most closely studied, Arctic foxes (Alopex lagopus) can be significant predators.
Lesser Snow Goose gander repelling Arctic Fox. Photo by Gustaf Samelius.
Nests defended by two adult Lesser Snow Geese (Chen caerulescens), a smaller species, are virtually invulnerable to foxes [Learn more about this research here].

Nests defended by only a single parent are more easily predated (Samelius and Alisauskas 2001). Perhaps fox predation helped shape the evolution of the colonial nesting habit, and other behaviours, among ground nesting geese.

Perhaps what we witnessed on this evening was the "release" of an anserine defensive repertoire that evolved primarily as a response to foxes. Perhaps this goose-stepping and fox-trotting are moments in a very ancient performance, danced by two intimate evolutionary partners.

Dugger, B. D., K. M. Dugger, and L. H. Fredrickson. 1994. Hooded Merganser (Lophodytes cucullatus). In The Birds of North America, No. 98 (A. Poole and F. Gill, Eds.). Philadelphia: The Academy of Natural Sciences; Washington, D.C.: The American Ornithologists’ Union.
Samelius G. and R.T. Alisauskas. 2001. Deterring arctic fox predation: the role of parental nest attendance by lesser snow geese. Canadian Journal of Zoology: 79: 861-866. Abstract.
Photo Credits:
Hooded Merganser courtesy of Susan Allen.
Lesser Snow Geese defending against Arctic Fox courtesy of Gustaf Samelius. Learn more about this research here.

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