Grey treefrog rejected as food by a fisher

Fisher (Martes pennanti). Photo: Mark Andrew Conboy.

Fishers (Martes pennanti) have become a relatively common species in Eastern Ontario over the past three decades but for such a potentially important predatory mammal we know very little about them at QUBS. Very few observations of the foraging behaviour and diet of fishers have been made at the station. Fishers have been seen eating and caching carrion in winter and pursing small mammals along rocky outcrops in spring.

Observing fisher foraging in real time is difficult, but following fisher tracks is an alternative method of gathering behavioural information. On February 28, 2010 I followed fisher tracks for 1.7 km on the Pangman Tract. Over that distance I noted one occasion where the fisher stopped to investigate a large bone, one scat deposit and four places where the fisher dug into the snow and/or the exposed leaf litter. Two of those digs were in the duff at the base of eastern white pines (Pinus strobus). Another dig was in the leaf litter beside a log. In all three cases it was impossible to determine what the fisher was digging for, but I suspected it may have been trying to find hibernating frogs. On the fourth dig I found a hole 13 cm deep through snow and humus beside which was a tetraploid grey treefrog (Hyla versicolor); the frog appeared to be dead, though it was not at all damaged by the fisher. Treefrogs normally freeze solid during hibernation but this frog was completely thawed. I took it back to the station to see if it would revive, but it never did.

Tetralpoid grey treefrog (Hyla versicolor) that was dug out of a hole (right) by a fisher. Photo: Mark Andrew Conboy.

At first I was puzzled by the fisher’s rejection of the treefrog, but Fred Schueler reminded me that grey treefrogs are unpalatable to shrews and probably other mammals. The bright orange-yellow markings on the treefrog’s legs probably serve as an aposmatic warning to would-be predators. Not all of our frogs are so distasteful. Wood frogs (Rana sylvatica), for example, also hibernate in the leaf litter and may have been the intended prey of the fisher. – Posted by Mark Conboy

Barred owl eats flying squirrel

Barred owl (Strix varia). Photo Paul Maritn.

The familiar refrain of the barred owl’s (Strix varia) song, Who-cooks-for-you?, is heard all year long at QUBS. But as far as barred owls go, we are not so much interested in who is doing the cooking as we are in who is being eaten. Across their range in North America barred owls take a wide variety of prey including mammals, birds, amphibians, reptiles and even fish (Mazur and James 2000), though they feed chiefly on small mammals such as voles, shrews and squirrels (Elderkin 1987). Studies have documented the diet of barred owls in some other parts of its range, but there is little information available about the diet of this species at QUBS specifically. Even though barred owls are a common and widespread species at the station, there appears to be no documentation of what they eat. Paul Martin and I collected a pellet from below the roosting site of a barred owl and dissected it to determine its contents. The barred owl was originally found by Paul Martin in an eastern white-cedar (Thuja occidentalis) near Cedar Cottage on February 28, 2010.

The pellet measured 65 × 25 mm, but was soft and probably somewhat deformed because it had been sitting in wet snow for much of the day. The pellet contained the remains of a single flying squirrel (Glaucomys sp.). The squirrel skull had been badly pulverised but some of the components, such as the lower jaws, were still intact enough to aid in identification. Each lower jaw had 1 incisor, 1 premolar and 3 molars. That dental formula indicated a sciurid. There are four small sciurids at QUBS: northern flying squirrel (G. sabrinus), southern flying squirrel (G. volans), American red squirrel (Tamiasciurus hudsonicus) and eastern chipmunk (Tamias striatus), all with the same lower jaw tooth configuration. We measured the lower jaw from the angular process to the tip of the dentary bone (= 18.4 mm). Our jaw measurements indicate one of the two flying squirrel species (Glaucomys sp.). We compared other components of the skull such as the ear capsules and cranium bones to photographs on the internet and in field guides to further corroborate our identification. The two flying squirrels are very similar and we were unable to find suitable reference material to allow us identify our specimen to species without a more intact skull. We welcome expert opinions on specific identification.

Selected components of the pellet; all are parts are from a flying squirrel (Glaucomys sp.). On the left: the lower jaws and whiskers. On the right: 6 leg bones, 2 ear capsules and the top of the cranium. Photo Mark Andrew Conboy.

Both flying squirrel species are possible at QUBS. Northern flying squirrel is known to occur but the status of southern flying squirrel is uncertain. Most published maps place QUBS well within the range of southern flying squirrel even though its distribution in Eastern Ontario is not perfectly known (see maps in COSEWIC 2006). Southern flying squirrel is considered less common than northern flying squirrel, which can be locally numerous though not often seen without concerted effort. To our knowledge there has not yet been a documented account of southern flying squirrel at QUBS.

– Post by Mark Andrew Conboy


COSEWIC. 2006. Assessment and update status report on the southern flying squirrel Glaucomys volans; Atlantic (Nova Soctia) population, Great Lakes Plains population.

Elderkin, M.F. 1987. The breeding and feeding ecology of a barred owl Strix varia Barton population in Kings County, Nova Scotia. Master’s Thesis. Acadia University.

Mazur, K.M. and James, P.C. 2000. Barred owl (Strix varia), The birds of North America online (Poole, A. editor). Ithaca: Cornell Lab of Ornithology.