Witness the Snowy Owl Population Fluctuation

Featured Species:  Snowy Owl

Sure you’ve seen Hedwig the Snowy Owl on screen (actually played by male  owls), but have you seen one of these stunners in real life?  The winter of 2011/12 may be good for sightings , as the appearance of white adult males often foreshadows an irruption and several have been reported in southern Ontario.  So keep your eyes open and let’s wait and see if this prediction comes true. 

Snowy Owls are arctic breeders. Every winter some show up in the south, often juveniles whose plumage is more flecked with brown (females are even more barred).  But every four years or so an irruption occurs.  Why?  Not because they aren’t adapted to the cold winters – their thick down allows them to maintain a body temperature of 37.8-40.0°C when it’s -57.0°C out (brrrr). The classic hypothesis posits a series of cycles.  After all, an owl has got to eat . It was thought that the irruptions are linked to crashes in lemming populations (their main food source) further north, which have a boom and bust cycle over three to four years.  When lemmings peak in the summer, owls fledge several chicks instead of just one or two.  This increase in population pushes young-of-the-year birds south.  On top of that, when the lemming population crashes, adult Snowies have to migrate south as well. Some scientists have recently suggested there is more to the story, since Christmas Bird Counts show that the numbers fluctuate irregularly from year to year, and lemming crashes are often more regional than the large-scale geographically synchronous owl migrations. Other factors such as snowfall and extreme temperature conditions may play a role. Some Snowy Owls may also migrate between Russia and Canada!

The mechanisms of lemming population crashes are not completely understood either, but one sure thing is that Disney had it wrong - they don’t commit suicide. Rather, population peaks lead to mass migrations (contains a good video), and the large numbers of lemmings become so focused on getting somewhere that they realize too late that they are accidentally enroute to fall off of stream banks and cliffs. It likely more complicated than this though, with many other factors contributing to the population crashes including infanticide, predation, starvation and disease.

Here is the south Snowies like open country with Meadow Voles, so be on the watch for the occasional Snowy on a fencepost , stump  or rise of ground.  They act remarkably tame, so while you can get quite close, please don’t try – you may stress starving birds, and reduce their chance of survival.  Be content with the large number of excellent, on-line close-ups.

Other Happenings:  

• Late this month, Great Gray Owls may also arrive for a winter sojourn.  Great Grays are largely rodent predators, and with their large facial disk and resulting sharp hearing, these owls can hear, and catch, rodents that are beneath 30 cm of snow.  Here’s their call (scroll down a bit) – it’s the prototypical “hoo, hoo!”.

• Our bird feeders have gotten very busy lately, with American Goldfinches and Black-capped Chickadees in particular.  Other places to look are any areas of open water (gulls, eagles, ducks), open fields (Snowy Owls, Red-tailed Hawks, Snow Buntings) and roadsides (winter finches -- review these forecasts and see if they come true in your region). 
• Recent snow means that fresh animal tracks can be easily identified and followed.  We may feature tracks later in the winter, but here’s a good, short, basic primer on tracks and tracking (go in particular to Tracks in the Snow).  Here are some simple track ideas for local field trips and the school yard.

• Porcupines and their sign are very evident now because they remain active throughout the winter and there are no leaves in the way.  This site provides a good visual history, including tracks in the snow, winter dens and feeding sign.

• With the holidays, we turn our attentions to the coniferous trees, analysing their shapes in debates on which to choose. Balsam Firs with their wonderful fragrance, steeple-shape, and long-lasting needles are favourites.

• In the Northern Hemisphere, the Winter Solstice occurs on December 22, 2011 at 12:30 AM EST.  At that time, the North Pole is tipped farthest from the sun, marking it the shortest day of the year, and the beginning of winter. Days will begin to get longer – reason for celebration  around the world. It has been  just three short months since the sun appeared to cross the equator during the fall equinox, and is just eight weeks before the first spring bird song.  Seasons occur because the earth’s axis of rotation is tilted 23.5^o relative to the plane of the Earth’s orbit around the sun.  No one knows why the Earth tilts , but imagine if it didn’t – the sun would always appear to be over the equator, and it would be spring/fall everywhere, all the time.  No seasons.

• On average, December is only slightly milder than the deep winter period of January/February.  The average daily maximum in the Kawarthas is -1.0^oC, and the average daily minimum is -10.4 ^oC.  The amount of rain and snow is in rough balance with 33.9mm or rain and 41.5cm of snow (1 mm of rain is equivalent to 1 cm of snow).  What about where you are?  Find long-term averages for a location near you and compare them to this year. 

• The Geminids meteor shower peaks on December 14 and 15.  This shower is considered to be one of the most active, and is the only one that does not originate from a passing comet.
        
  

Happy holidays (catch the full moon on December 10 and the new moon on Christmas Eve ), and see you in January 2012 (International year of Sustainable Energy for All ).