10 October 2012
When Canadians spot migratory ducks and geese, we know that the seasons are changing. But these flocks are just part of the over 500 species of migratory birds that make Canada their home for a time.
As the days shorten in autumn, the birds return to warmer regions where the available food supply varies little with the season.
Most migrations begin with the birds starting off in a broad front. Often this front narrows into one or more preferred routes termed ‘flyways’. These routes typically follow mountain ranges or coastlines, sometimes rivers, and may take advantage of updrafts and other wind patterns or avoid geographical barriers such as large stretches of open water. The specific routes may be genetically programmed or learned to varying degrees. The routes taken on forward and return migration are often different.
Geese in a V-formation may conserve 12 – 20% of the energy they would need to fly alone.
Unfortunately, many of the world’s migratory birds are in decline. Along the flyway, important habitats for migrants are under threat from infrastructure and housing development, energy development (mining and drilling for fossil fuels), tropical deforestation and the spread and intensification of agriculture.
The Rocky Mountain Trench is part of the ‘Pacific Americas Flyway’ which extends along the western flank of North and South America.
At Elizabeth lake this week, naturalists enjoyed the antics of Yellow-rumped Warblers. One tall shrub filled with half a dozen of the streaky brown-and-yellow birds giving their distinctive sharp ‘chips’. Yellow-rumped Warblers are fairly large, full-bodied warblers with a large head, sturdy bill and long, narrow tail. Weighing less than half an ounce, these birds forage in the outer tree canopies at middle heights and ‘sally’ out to catch insects in mid-air. They cling to the bark surface to look for hidden insects more than many warblers do. Their flight is agile and swift, and the birds often call as they change direction. Their populations are stable or increasing in most areas.
Join the Rocky Mountain Naturalists for early morning birding at Confederation Park adjacent to Elizabeth Lake at 7:30 am on Tuesdays until mid-October.
Elizabeth Lake, October 9th. (33 sp)
Submitted by Daryl Calder.