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

References

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.

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