Strictly for the Birds!
An Urban Ravine – What’s in it for the Birds?, by Greg Sadowski
For thousands of years since the last ice age, songbirds have been making the perilous journey from their breeding grounds in northern forests to their rich winter foraging grounds in central and south America. Tens of thousands of young songbirds on their first fall migration filter down from places as far afield as northern Manitoba through the forests of southern Ontario, using the many creek and river systems as readily recognizable highways on their trek south. An important rendezvous for many of these birds has always been the northern shore of Lake Ontario. From here the birds can either head west following the shoreline to find easy crossing points at the junctions between the Great Lakes, or if conditions are favourable, they can simply head straight across the lake on clear, calm nights.
This journey is already dangerous enough, as inexperienced birds only a few months old attempt to locate food and shelter in unfamiliar forests. But during the last hundred years or so, and particularly in the past few decades, a new obstacle to their southward push has emerged. Rapid urbanization of the landscape in southern Ontario has concentrated what was once a fairly broad front of migration into ever narrower corridors along the creek and river valleys. It is these valleys that are now absolutely crucial to the survival of a wide variety of songbird species – crucial because it is along these remnants of natural cover that the songbirds are able to feed and build up their fat reserves to fuel their flights across Lake Ontario.
So it is easy to comprehend how the continued loss or degradation of ravine systems has far-reaching effects on the health of bird populations in areas well-beyond our urban limits. Birds such as Wilson’s warblers and grey-cheeked thrushes cross hundreds of miles of natural cover, only to find themselves pulled up short on the approach to Lake Ontario. Wouldn’t it be better if, instead of always creating obstacles that slowly drag these species down, we could restore some safe and comfortable rest-stops for these intrepid but exhausted travelers? By improving the natural cover – and thereby both the foraging and shelter opportunities – in urban ravines, we can give these travelers the extra boost they need to successfully complete their great adventure.
The Bartley Smith Greenway is one of many north-south valley corridors in the GTA that songbirds use as migration routes, and the habitat restoration that has taken place in the past few years just might contribute to the survival of a few more birds for another season.
1- Myrle Warbler; 2- Magnolia Warbler; 4- Cape May Warbler;
5- Blackburnian Warbler; 6- Indigo Bunting; 7- White-throated Sparrow;
8- Wilson’s Warbler; 9- Blue-headed Vireo; 10- Black and White Warbler;
11- Northern Parula; 12- Veery; 13- Rusty Blackbird; 14- Scarlet Tanager; 15- Ovenbird.
