Apparently hummingbirds can survive up to minus 20C. There were sightings of rufous hummingbirds last December, in Eganville and Ottawa. What the heck do they eat at that time of year? All the flowers are gone, so no nectar there. The tree sap isn't running any more, so no food there either. Even those sugar water feeders freeze at that temp (personally, I think hummingbirds need nectar, not sugar). Another of nature's mysteries...