Nature Wise: When do you think spring has arrived?

Officially spring arrives when the sun crosses the equator on its journey north from its southernmost point.

Officially spring arrives when the sun crosses the equator on its journey north from its southernmost point — this is known as the vernal (or spring) equinox.

On this day the daylight hours are equal to the nighttime hours.  The timing of the equinox varies a little each year; it can be as early as March 20 (as it is this year) or as late as March 22. Because of this variation in timing much of our statistical weather data operates on the assumption that spring begins on March 1 and ends on May 31. But many of us have our own definition of when spring begins.

We all think of spring as a time of warming weather, trees budding out, flowers blooming, etc. and of course this all happens. But even though the spring equinox occurs on the same date no matter where on Earth you live in the northern hemisphere, these signs of spring occur at vastly different times based on where you live.

Differences in latitude (how far north you are), differences in elevation and even differences in how far you are from a large body of water all affect when spring arrives in your neighbourhood.

Some people have their own criterion for when spring arrives — the timing of the first pussy willows or perhaps when they see the first swallow flitting about.

Here in the Okanagan Valley the arrival of the Western Meadowlarks might be appropriate since historically the main migration of Meadowlarks occurs in the first week of March.  Note however that a few Meadowlarks stay all winter — this past winter Penticton had at least two Meadowlarks at Christmas time. Perhaps the appearance of our iconic Arrowleaf Balsamroot flower is a better sign of spring since none of them bloom in winter.

But no matter how you define it, spring brings one of nature’s many miracles, spring bird migration. Even though I’ve read many books on the subject and watched birds migrating for many years, I still find it amazing to contemplate the journeys undertaken by so many of our “local” birds and the different, but very regular, timings of the various species.  Even closely related birds don’t all migrate at the same time.  Amongst the swallows, violet green and tree swallows return to the valley around the end of February, whereas their cousins the barn swallows don’t show up in great numbers until May.

If you listen to the cranes flying over you don’t need a calendar to know it’s April — the large flocks of these great birds are like clockwork — the last three weeks of April with few exceptions.  A bit late for defining the arrival of spring, but impressive nevertheless.

When I was a kid, the appearance of robins was often heralded as a sign of spring and that may still be true in some parts of British Columbia. Here in the valley, though, more and more robins are present year-round, although many do still migrate with the main arrival date historically being the second week of March.

The large amount of bird migration data accumulated over the past 60 years or so show that a large number of birds (27 species out of 96 studied) are arriving back in Canada significantly earlier than they were previously and in many cases, consequently  are also nesting and breeding earlier.  Climate change, no matter its cause, is definitely having an effect on the bird world. However, the climate has changed many times in the past million years so this is not unprecedented — although the speed with which it is occurring may be. Birds have adapted to changing climate in the past — can they do so this time?

The next meeting of the South Okanagan Naturalists’ Club will be March 24. The public is always welcome.  Check out our website (southokanagannature.com) for details about our monthly speaker.

Bob Handfield is president of the South Okanagan Naturalists’ Club but the views expressed here are his own and do not necessarily reflect the position of the Club.

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