BACKYARD DECLINES - DO WE WORRY ?

Wednesday, July 09, 2008

Often I get phone calls about vanishing birds - not as many orioles as last year in my yard, or that my goldfinches have suddenly left my feeder. My barn swallows aren’t here this year. What am I doing wrong?

Probably nothing. Birds tend to be very nomadic and fluctuations in local populations can occur from one year to the next for no particular reason. If declines, or conversely increases, are gradual, over a period of many years, then it becomes easier to assign a cause. You may have seen, as have I, the decline in those huge flocks of tree swallows that used to arrive in the morning in July and August, and cover the trees and utility wires, so great were their numbers. Numbers were particularly high in areas of cattail marshes, as it is here where congregating tree swallows like to roost at night, after the nesting season is over for the year. Then it’s off to the daytime perches at the first break of light.

Or, at least, that’s the way it used to be, when I remember enormous clouds of tree swallows filling the eastern sky at twilight in the fall of the year as they’d gather in our weeping willows and on the hydro wires that passed by our house on the farm, just a kilometre from where we now live. It just doesn’t happen anymore, and with few exceptions, tree swallows simply quietly disappear from the scene in the fall, with little fanfare. Experts say the population has declined to almost half the population it was 25 years ago. Barn swallows, wood pewees, nighthawks and chimney swifts have also been in decline, interestingly, all insect eaters. Is it just a local thing, or is it more widespread, suggesting something more complex?

For other species, change in their numbers can be related to habitat change. The vesper sparrows that once nested on our old farm in large numbers, have all disappeared. Many of the fields in which they once nested have been abandoned, and have succumbed to natural plant and tree succession. They simply have moved on to more hospitable abodes. In a field where killdeers and meadowlarks once cohabited, encroaching red cedars have welcomed another species, that hadn’t been on the farm checklist prior to the 1980s - the clay-colored sparrow. It is a specialist, and seeks out meadows that contain a few invading cedars, but not too many, for once the field becomes thick, it will move elsewhere where conditions are more favourable.

Backyards can offer a similar scenario. When my wife and I moved to our lot in 1976, the two acres had only remnants of an oat field and a hay field. Not a single bush or tree existed. In fact, the first species to be recorded when we staked out our fence border was, strangely enough, a rare sedge wren, who wheezed out his determined song for several weeks in the tall grasses. The lot was, in fact, so barren, that even killdeers exhibited some reluctance to chance the wide open spaces.

Today, killdeers have totally disappeared from our two acres, and this year we had both catbirds and brown thrashers nest in our hedgerows and bushes, and warbling vireos nested for the first time in our silver maples. There was even a pair of cedar waxwings whose nest I never did track down. The habitat has changed, and we deliberately chose native bushes and trees that produced the seeds and berries that would attract what we wanted. Today, it is a treat to sit under our spreading maple tree and watch the variety of wildlife that we now have - birds, snakes, turtles, moths and butterflies - things we never had before. We are now at a point where we are not sure what is attracting who, and are at a loss to explain the behaviour of some of our guests, like the wild turkey that followed me around as I was using the weed eater one day last year.

There is no question that as our human population explodes by 80 million people every year, the world will continue to see declines of many wildlife species. Disappearing habitat, migration hazards - all are sounding the death knell for many. Creating wildlife habitat as we have done will not save the world, but it does allow us to enjoy what we have left for a bit longer, in our own backyards.

Many species are not as common as they once were. That much we know. However, the temporary disappearance of backyard orioles, hummingbirds, swallows or goldfinches through the seasons is nothing to worry about, unless it continues to take place over many decades. It could be little more than some favourite bushes or trees being removed from the setting, a change in available food, or just the whims of the bird in question to roam.