(This 843rd Buffalo Sunday News column was first published on May 20, 2007.)
Tree Swallows at a bluebird nestbox
Photo by Glenn Clark
There are many so-called ornithological signs of spring. The first robin or the first bluebird are two such signs. But individuals of those species often stay here through the winter. To me a better and truer signal of spring has always been the arrival of tree swallows.
Tree swallows are very attractive birds. The backs of the males are a glossy metallic blue with green hints, their breasts bright white. The demarcation between the colors is sharp, giving them a well-dressed appearance. The color of the females is similar but not as bright. In fall young tree swallows have brown backs and are easy to confuse with bank or rough-winged swallows.
Like other swallows, the flight of tree swallows is rapid and erratic. They seem to be constantly testing their equipment to see if it can withstand even more sudden changes of direction. Although their dashing about is mostly to catch flying insects, I seldom see swallows flying in straight paths even when they appear not to be feeding.
A late March or early April visit to the Cayuga Pool at Iroquois National Wildlife Refuge or at Times Beach or Tifft Nature Preserve on Lake Erie will often disclose a few of these early tree swallows zipping about over the water in a largely futile search for the insects that are not yet hatched at that time of year.
But unlike the other birds of their genus that would not appear for at least a week, these natty tree swallows have acquired an adaptation that gives them an advantage. Those cousins -- barn, bank, cliff and rough-winged swallows and purple martins -- eat only insects. Tree swallows on the other hand are not so limited. They eat berries as well. They are especially fond of bayberries but stomach analyses produced other berries and even rose thorns. In fact, a fifth of tree swallow food is vegetative.
Those stomach analyses were carried out in what many contemporaries would call the bad old days. Back then, over a century ago, professional ornithologists collected -- a platitude for killed -- hundreds of birds, in the case of tree swallows 343 in just one such study, in order to open their guts and determine their feeding habits. Times have indeed changed but those data continue to provide us insights into bird behavior such as this.
In any case tree swallows have always appeared to me to be well prepared to be perfect harbingers of spring.
Sadly, this year tested that belief -- on their part as well as mine. And many tree swallows failed the test. Almost as many as those swallows that were killed to study stomachs were found dead this spring in nest boxes at the Iroquois Refuge. A total of 234 swallows died in those boxes set out primarily for bluebirds.
This past winter was indeed an unusual one. It didn't even start until mid-January. Until then it was arguably the mildest season on record. I would have bet that Lake Erie was too warm to freeze. I would, of course, have lost that bet. And mid-April brought some of the worst of that half-winter. Here is how Steve Mclaughlin of the Buffalo Forecast Office summarized this period: "After the promising mild spell in late March extended over into the first few days of April the pattern changed abruptly and gave us some of the coldest April weather in memory during the next two weeks as a deep low set up across eastern North America. This period included a rare lake effect event as well as an elevation type storm at mid month. The two week period of the 5th to the 18th was nine degrees below normal daily and featured four days of consistent subfreezing temperatures."
The hardiness of those early migrants was overwhelmed by this weather. Even though they shared their body heat with others of their kind in those nest boxes, this time the cold was too much for them. Their hypothermia deepened and many of those tiny lives slowly flickered out.
Not all local tree swallows died in that unusually protracted cold snap, thank goodness, but that loss underscores once again how fragile is life on earth.-- Gerry Rising