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Witness the Snowy Owl Population Fluctuation

Mid-Late December 2015


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 2013/14 was great for sightings, as there was a significant irruption throughout Canada and the U.S.  Last winter was a reasonable one for Snowys, but this fall may presage another bumper winter, with early sightings clustered in the upper U.S. midwest and Manitoba.  So keep your eyes open in case we have another good winter for these magnificent birds. 

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, disease and global warming.

Here in 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!”.
  • 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 signs 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 21, 2015 at 11:48 PM 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 (scroll down). 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 23.5o relative to the plane of the Earth’s orbit around the sun.  No one knows for certain why the Earth tilts, but we have a fair idea.  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.  What about where you are?  Find long-term averages for a location near you and compare them to this year. 
  • The Geminid meteor shower peaks on December 13 or 14, and is best seen after moonset, or 9 P.M. and later, peaking after midnight.  This shower is considered to be one of the most active, and is the only one that does not originate from a passing comet. 
  • A minor shower, the Ursid, occurs around the solstice and radiates near the Little Dipper. 
  • The Cold, or Long Night full moon rises the evening of the 24th, while Mercury can now be seen in the western sky after sunset late in December, setting about 90 minutes after the sun.  Jupiter rises to the east around midnight, and pairs up with the moon on night of the 30/31st.

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