Thursday, April 27, 2006

Cooper's Hawk takes Rock Pigeon

Click to view a substantially larger image.
Almost all of the birds we observe at our feeders are the native species one would expect in cottage country. Exceptions include three European Starlings (Sturnus vulgaris) that showed up for the first time this past month. Only once before have Martha and I seen feral Rock Pigeons (Columba livia) from our property, a high-flying flock that wheeled over our bay, heading west in high gear last September. We know of a few small flocks, several km to the north and south, that take advantage of the shelter and nesting opportunities afforded by bridges along Highway 28. Perhaps it was such an overflying trio that observed the many Common Grackles (Quiscalus quiscula), Brown-headed Cowbirds (Molothrus ater) and Red-winged Blackbirds (Agelaius phoeniceus) at our feeders on April 23rd. The pigeons landed, tasted the cracked corn and so joined the list of 30 or so other species we've observed at the feeders. Since then, the same three Rock Pigeons have visited two or three times each day.

Late this morning, I glanced out the window and saw the three Rock Pigeons feeding along side a mixed flock of 30 or so blackbirds. The birds suddenly scattered - they are often startled by the construction-related traffic at the barge landing on our neighbour's lot. I then saw a fair-sized bird make contact with one of the fleeing Rock Pigeons and the two cartwheeled to the grass, just down slope from the feeders.

I called Martha from the kitchen and over the next five minutes, we watched the Cooper's Hawk (Accipiter cooperii) subdue and pluck the hapless dove. We were able to get a few blurry pictures by "digiscoping" our Coolpix 4500 against an 8 x 40 binocular objective. Our observations ended when an approaching motorboat flushed the hawk, which flew down slope to the east with its prey in its talons.

The pictures convey the rest of the story.

Our resident Canada Geese, celebrated below in their routing of a Red Fox, were unruffled by this particular predator. Indeed the two geese approached, on webbed feet, to within five metres of the hawk and quietly observed the pigeon's demise.

The two other Rock Pigeons returned to the feeder an hour or so later.

Saturday, April 22, 2006

Tho' nature, red in tooth and claw

Portions of small mammal skulls from a single owl pellet
Every few months we hear the call of the resident Barred Owls and a few times, I've caught glimpses of them flying across the beams of the truck headlights. This winter, a few Great Gray Owls were in the area and on Long Lake Road, only a few kilometres to the north of us, a cottager found an injured Boreal Owl under a window last month. Overall, I think our encounters with any of the resident species are rare.
Martha spotted an intact owl pellet lying beneath a Hemlock deep in the woods. When we teased it apart, we found the remains of at least three small mammals.

Two of the partial skulls and a single mandible are from shrews (family Soricidae) of the subfamily Soricinae, also known as the Red-toothed Shrews. The reddish colour is the result of iron deposited in the tooth enamel. Not represented here are members of the subfamily Crocidurinae, or White-toothed Shrews, a taxon comprised of species not found in the New World.

The first and third partial skulls are likely from Northern Short-tailed Shrew (Blarina brevicauda. The second (middle) skull is likely from a Meadow Vole (Microtus pennsylvanicus). These two widespread species are common in the area.


The title of the entry was borrowed from In Memorium A.H.H, by Alfred Lord Tennyson (1850).

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.