Snowy Owls in Southern Ontario - Studying their diet

Nature Notes for February 28, 2014

What on earth is that young woman doing, digging about in the snow at the foot of a utility pole? If you have stumbled on a scene like this in the past few weeks, you have probably come upon a scientist looking for owl pellets.

The Ministry of Natural Resources is collecting Snowy and Short-eared Owl pellets for a long term diet study to evaluate what they eat during the winter months and how their prey cycles over many years.

So far, the team has found Snowy pellets in Peterborough, Kingston, Wolfe Island, Amherst Island and Dufferin County and Short-eared pellets in Hamilton and Fisherville.

Because very few Short-eared Owls occur in Northumberland County, the rest of this column will be about Snowy Owls. This winter, there have been a number of Snowy Owls in Northumberland County, too. However, these birds have chosen to roost in completely inaccessible locations such as the ice or icy headland at Cobourg Harbour, the ice on Presqu’ile Bay, the ice along the Port Hope waterfront and on the top of farm silos. The searchers have tried, but had no luck finding pellets here.

What are these pellets? Owls usually swallow their prey whole. The birds’ digestive systems collect the indigestible parts of their prey – fur, feathers and bone – into pellets which the birds then spit up. By collecting pellets and tearing them apart, researchers can determine what the bird has been eating.

Snowy Owls nest in the high Arctic where their primary food is rodents called lemmings. In the summer of 2013, the lemming population was very high, so the owls had lots of food. This meant that a higher than usual number of the nestlings survived to leave the nest. However, when winter set in, there was not enough food for so many owls. Many fled south.

This winter, Snowy Owls have been seen throughout eastern North America as far south as Florida.

When Snowy Owls come south, they search out areas which are similar to the ones they occupy in the Arctic. That is, open, treeless expanses. In southern Ontario, this means that they can often be found on windswept beaches, agricultural fields and airports. Most airports have catch and relocate programs for Snowy Owls (and other raptors), since a collision between an airplane and an owl would not be good for either.

Although Snowy Owls favour lemmings as prey on the breeding grounds, they will switch to other prey if lemmings are not available. Other rodents – voles, mice, rats – are acceptable prey. The owl which has been frequenting Cobourg Harbour this winter has learned that ducks can provide a tasty meal. One seen recently on the Port Hope waterfront also had Red-breasted Merganser bits at its feet.

Unlike many owl species, Snowys are active in the daytime. In the long days of an Arctic summer, they have to hunt in daylight.

Snowy Owls are the heaviest of the owls that occur in North America. They are heavily feathered, even to their legs and feet as protection against the cold. As with most raptors, the females are larger than the males. The sexes can be differentiated in the field by the amount of black barring. Females have more barring than the males. Older males can be almost completely white. This was a casting error in the Harry Potter movies, where Harry’s owl, Hedwig (supposedly a female) was played by a clearly small and very white male.

If you know of a roosting Snowy Owl or Short-eared Owl, the MNR team would be pleased to hear from you. Contact Sarah at slmcguire@gmail.com. As I write this, she was busily sorting the bones from collected pellets.