BASKING IN HOT WEATHER  

Wednesday, July 01, 2009

       There was a wood thrush sending out its flute-like notes as we walked along in the heavily forested Cassidy Block, east of Thomasburg last week. Had we been in the open and away from the shade of the forest canopy, it would have been far too hot to enjoy a hike, and certainly little sign of wildlife. Few birds sing in this kind of weather.  It is a time when most birds are quiet as they go through the stressful period of moulting.
 
However, we still listened for there were a few voices out there, all of them hidden, as might be expected, by the dense foliage. There were the quick phrases of at least one, perhaps two, American redstarts. Unlike many of the 30 or so warbler species that pass through this way every spring on their way to nest in the boreal forests, the redstart is quite content to set up housekeeping locally. For reasons best known to them, they seem to remain vocal through the summer heat, whatever the temperature.
 
There was another forest resident who we had not heard from yet - the denizen of summer woodlands. It was odd that in the space of 15 minutes, one had not shown up. Then we heard it. The loud, monotonous phrases of a red-eyed vireo echoed through the dense canopy ahead of us like a musician with his amplifier set to reverberation.
 
It never stopped singing during the time we were there, seemingly following us as though fascinated by our presence on such a warm day. Its small size was lost in the dense canopy, but the persistent song almost pinpointed its location high in the trees. It is said that one researcher spent an entire day painstakingly counting the songs that one individual produced from the moment it started at daybreak. By day’s end, the fatigued researcher had tabulated 22,197 songs, all delivered by the single bird in the space of one day. Certainly an amazing feat for a small bird, not to mention the researcher who followed the bird around all day with his pencil and paper.
 
The cheerful song is tiresome, chiefly because most of the phrases end with a rising inflection, giving the impression of a long series of interrogations, the voice seldom resting before delivering the next note. The end result is a never-ending repetition that resembles an ongoing telephone conversation.
 
These vireos have good reason to be buried in the thick foliage of trees, for here is where they find the caterpillars of webworms, gypsy moths and others tree feeding insects. Here they will nest too, where they can be close to their food supply. Like their cousin the warbling vireo, the tiny nest of tightly woven grasses, spider webs and fine plant material is suspended in the fork of a horizontal branch.
 
But these vireos are in trouble. Once considered one of the three most abundant forest birds in North America, populations have been steadily declining. Due to fragmentation of forests, parasitic cowbirds are penetrating the interior of smaller woodlands resulting in the vireo nest being a primary target. Cowbird eggs hatch earlier than those of the vireo resulting in the young cowbirds out competing the young vireos for food and space. Because these birds are effective at controlling insect pests, the declining populations are a matter of concern.
 
The persistent song we hear now in the woods will decline as fall approaches. As the fall migration accelerates, we will not see red-eyed vireos as we would see flocks of sparrows or warblers, but rather as individual birds, moving about in complete silence as they search for remaining insects. Average departure around here is October 4, but come May 12 - later than many spring migrants - they will reappear and begin their robin-like phrases once again.