Vol. 15 No. 2
"In all things of nature there is something of the marvelous" - Aristotle
In this issue...
Reflections on the Spring Chill
on the Spring Chill
I'm watching the snowflakes begin to fly, again. Lifelong Michigan residents find this weather and its resultant pause in spring migration -- annoying, but somehow "typical," although this is actually the longest stretch of April cold in this region since 1982. This cold spell, however, has extended all across the eastern United States, and will end up being far more than inconvenient for migrant birds. It is likely to have a profound and longlasting impact on bird populations.
Already, many insectivorous birds in the south have perished. Last weekend in south Texas, a birder reported "over a hundred swallows on the windows, patio chairs, and palms just outside the door of [a neighbor's] home. I counted over 60 by the time I got there and took photos of 20 or so on one palm branch ...2 and 3 deep. We identified barn, cliff, and bank swallows perched on the window sills, patio chairs, all huddled together." These reports continued through yesterday - the Chimney Swifts and swallows that are not succumbing to cold and starvation are foraging very low to the ground, especially near roadways where the pavement generates some warmth and attracts insects. These birds are being killed in great numbers along highways.
My real concern is for the migrants that have yet to arrive. Deciduous trees that were leafed out and/or blooming have been devastated from the Gulf coast northward. Oaks were in full bloom in the south-central states, but the blooms are reported now to be brown and crumbling, so acorn crops in those areas are likely to be nil. In eastern Kentucky, this was reported for black oaks. In central Kentucky, a wider variety. Trees that had produced tender new leaf growth have had these leaves blackened. In the Knoxville area, hickories, black gums, maples, redbuds, locusts, and tulip trees are all brown. Also in Tennessee, one observer indicates that spring canopy foliage may be reduced 50-80%. In South Carolina, Bill Hilton gives a very sobering report of complete leaf kill on all shagbark hickories, hackberries, trumpet creeper, winged sumacs, and oaks, and heavy freeze damage to walnuts, mulberries, and aboveground foliage of Virginia creepers, wild grapes, and poison ivy, among others.
Beyond what insects were directly killed by freezing weather, the reduction in leaves will also mean that there will be less foliage available to insects and therefore fewer insects available to birds during migration. This could have serious consequences for migrants if they are unable to successfully refuel during the journey north. If trees used up reserves producing the spring flush of leaves, this foliage reduction may persist throughout the summer; the concomitant reduction in insects available for nesting birds will surely impact reproductive success. For tree species in which even woody growth dies back due to a prolonged freeze, reduced foliage growth or flowering could persist for the next few years. It is this reduction in foliage-consuming insects that has me most concerned.
Birds that manage to make it through the migration and breeding seasons will not have overcome their final obstacles. Over much of the eastern U.S., the fruit crop will be significantly diminished. I've read reports from Kentucky and Tennessee that dogwoods, wild plums, spicebush, blueberries, black cherries, and other early bloomers will probably set little or no fruit at all this year. In central Kentucky, holly shoots have been burned back from frost, and may not produce flowers and berries this year.
mean to sound alarmist. Climate events like this are not unprecedented
in history, of course, and bird populations have had to deal with them
before. But so many species are facing other pressures that they are not
adapted to deal with - large-scale habitat loss and fragmentation in particular
- that it may be that the spring chill of 2007 could have very long-lasting