Category Archives: Foraging/ Diet

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.

Bald eagles & coyotes

Posted by: Raleigh Robertson

On the morning of 3 February 2010,  at about 8 AM,  looking across the lake from our farm on Lake Opinicon, I spotted some activities near the far shore.  With my spotting scope, I discovered there were 2 Bald Eagles and 2 Ravens, feeding on a deer carcass.  It appeared to be a relatively fresh kill, since I could see the birds pulling on meat that wasn’t frozen, even though it had been minus 10 C overnight.  The Eagle plumage was quite distinctive, indicating one 2nd year, and one 3rd year.  About an hour later, there were 3 coyotes at the kill.  All were beautiful animals, in excellent pelage.  From watching urination events, I think one was male, one female, and the third, of unknown sex, was definitely subordinate – it consistently was submissive to the other two, and it often stayed off to the side, seeming to act like a sentinel.  The coyotes were eating, but also trying to haul the carcass over to the shoreline.  I later walked across the ice to check out the carcass, which was about 20 m from the far shore.  It was indeed fresh, meat along backbone still unfrozen, and it had been mostly consumed.  It was a small doe, possibly a yearling.  I think it was likely killed by coyotes during the night (the ice on the lake was quite bare, smooth and slippery,  following heavy rains a week ago, so a deer driven to the lake by coyotes would have very little traction), and then the pack of coyotes would have gorged on it, eating much of the meat.  Then at daylight, the scavenger birds had come in.  When watching the coyotes, I saw one taking a deer leg off into the woods, so the carcass was largely dismembered by 9 AM.  By about 10 AM, the coyotes were gone, and there was an adult Bald Eagle feeding at the carcass.   Then, by about 1 PM, there was a second year Bald Eagle at the carcass, and finally, at about 4 PM, there were 5 eagles and 2 ravens at the carcass.  The 5 eagles included 2 juveniles, one 2nd year, one 3rd year, and one uncertain, probably 2nd or 3rd year.

Interestingly, in later browsing the Bird Studies Canada website, and following their links to the eagle tracker –  based on the movements of Spirit, a bird tagged with a satellite transmitter in 2006, it is possible that the adult eagle I saw was this bird.  It’s location at the time seemed to be very much centred around Lake Opinicon.

Fisher & bloody tracks …

Posted by: Raleigh Robertson.

On Tuesday (2 Feb 2010) morning, from our back porch at our farm on Opinicon, I saw a fisher cross the path under the hydro

The blood covered red cedar, one week later, after lots of the blood had been rubbed off by subsequent antler rubbing. Click on picture for larger version.

corridor, about 40 m W of the house.  It was headed toward the lake, then went up the ridge to the south.  When I went out to look at its tracks in the fresh snow, I saw lots of blood, and at first thought the fisher had just killed a grouse or rabbit.  However, after more tracking I realized the blood, which was very fresh, and with sprays, as from a small artery, was from a deer – I could see three different spots where the deer had lain down, and a pool of blood formed.  When I backtracked, I discovered a small red cedar where a deer had presumably rubbed its antlers, and the 10 cm trunk was completely blood covered up to about 50 cm from the ground.  In the past, I’ve seen lots of cedars that deer had used to rub antlers, but never had I seen evidence of blood.  I’d be interested to hear of other observations of blood covered antler-rubbing trees.  In any case,  I think the deer had done its thing, and then the fisher had smelled the blood and had come to check it out.  Lois and I later searched for dropped antlers, but found none.