A Natural View: Migrating Birds Face Numerous Hazards

Terry Sprague

The American woodcock is one of the early birds among the spring migrants,
but unexpected snowstorms and freezing temperatures are a hazard to them.
(Photo by Peter Sporring of Belleville.)
[This article ran in the April/May 2009 issue of The SCOOP.]

I get many telephone calls from concerned people who find dead birds. Understandably, most want to know why the bird may have died. While there are sometimes obvious causes, often their time has simply come, and they expire in mid-flight. Perhaps that's what happened to the desiccated peregrine falcon we found one autumn on Main Duck Island. Or the banded chipping sparrow found dead in a backyard some years back. Banding records indicated that the bird was banded four years earlier at the Prince Edward Point Bird Observatory, and who knows how old it was when banded? Given the hazards birds must face daily, four or five years is pretty old for a tiny sparrow.

And migration hazards continue to increase in the form of high rises, communication towers, observation decks, and other tall structures, especially if these structures are ablaze with lights. The Lennox Generating Plant at Bath for example in 1981 resulted in a tally of 10,718 birds killed in two nights when they were attracted to the floodlights illuminating the 200-metre high chimneys. Through the efforts of the Kingston Field Naturalists, the hydro company changed the floodlights to strobe lights which cut down mortality significantly. We wonder about the current obsession with wind turbines - so many of them. They dominate the landscape at Wolfe Island, and soon will be dotting the south shore of Prince Edward County, incredibly, right in the middle of what has been designated by Environment Canada as an Important Bird Area. Will birds instinctively avoid them, or will a low ceiling one stormy night lead thousands to their death as they land in this well know staging area?

Toronto's CN Tower at 1,800 feet and at least 40 other Toronto buildings have been identified as major contributors to bird mortality during migration. But the all-time record is held by a southern U.S. airport whose upward aimed floodlights attracted migrating birds which flew in dazed circles until they died from exhaustion. The final toll was in excess of 100,000 birds.

Many migratory birds face other hazards during the spring migration, not the least of which is abrupt weather change. This was vividly demonstrated in mid-May of 1976 when four days of rain, snow and freezing temperatures led to the death of many swallows and swifts at Prince Edward Point in Prince Edward County. And how can we forget the thousands of tree swallows in just Prince Edward County alone that succumbed to similar unseasonable weather in April of 2003. Lawns in some areas were littered with hundreds of carcasses, and dozens were found in nesting boxes frozen to death. A purple martin that once arrived optimistically to a local martin house on April 2nd, was predictably found dead in five days after temperatures overnight had plummeted to minus six, accompanied by wind chills of minus 12.

As the human population increases, there will be even more challenges to the thousands of songbirds that migrate to and from their nesting grounds annually. Fortunately measures are being taken in many cases during the construction of buildings to reduce the frequency of avian collisions. Weather, unfortunately, we have little control over, and bird mortality will continue in the wake of late winter snowstorms, tornadoes, and other weather disturbances.

Even after the birds arrive there are still other hazards which birds must contend with, not the least of which is discarded monofilament fishing line. Waterfowl in particular encounter tangled clumps of it in the water and become snared when unable to escape, and eventually drown. Nesting songbirds suffer the same fate by asphyxiation when using what they perceive to be ideal nesting material. The lock stations along the Rideau Canal are favourite locations for anglers. A kayak trip I enjoyed one year from Kingston to Ottawa was darkened by the sight of huge clumps of discarded fishing line in the water at virtually every lock station, despite garbage containers being only metres away. Now it is balloons we are concerned about. The best we can do is to continue educating the public in our effort to lessen these unfortunate encounters.

And then there are the warblers, dozens of species, that winter as far south as Brazil and every May, without fail, they make the long journey to the boreal forests of northern Ontario, avoiding hazards along the way. How do they do it, year after year, even when encountering optimum conditions? They must possess some sort of unseen guiding force as they undertake these incredible migrations each spring, many of them avoiding the obstructions, predators, weather and other hazards that befall them along the way, returning to their favourite haunts to be viewed by the binocular brigade. I am sure the rare fork-tailed flycatcher sighted last fall had no idea what all the fuss was about as dozens of birders from across Ontario peered and gawked at the uncommon bird far from South America; very much alive and unaffected by hazards along the way,  it hawked for insects in a remote corner of Prince Edward County.  Many do succeed in making long journeys, but they are the fortunate few.

For more information on birding and nature and guided hikes, check out the NatureStuff website at www.naturestuff.net.

Migrating each spring from the West Indies and the Yucatan,
the black-throated blue warbler often nests as far north as Kapuskasing,
avoiding common hazards along the way.
(Photo by Adam Penson of Toronto.)