Wednesday, October 1, 2014

A Challenge to Hawkwatchers

How to find migrating hawks in the Southern Appalachians

We all know that migrating hawks achieve their long flights via soaring flight. Soaring flight requires certain meteorological conditions in conjunction with local topography. The two primary sources of soaring flight are the solar induced thermal and ridge crossing winds. The primary means of soaring flight is the solar induced thermal. Solar induced thermals will exist as long as the sun is illuminating the landscape. Ridge crossing winds will only exist when a high pressure system is opposite a low pressure system on opposite sides of the ridge. Therefore thermal soaring is the rule and ridge lift soaring is the exception to the rule.

Solar induced thermals can exist anywhere in the hawkwatchers purview. That purview is limited to three quarters of a mile for a Broad-winged hawk seen by the naked eye. Add an optical enhancement and that purview may be increased to perhaps two miles for a Broadwinged sized hawk. But, the fact remains that a hawkwatcher visiting a so-called hawkwatching site must know that the site is surrounded by terrain that produces solar induced thermals.

That brings us to Harvey's Knob. Harvey's Knob is rife with terrain that produces solar induced thermals prior to the Autumnal Equinox that occurs around September 21 each year. After the Autumnal Equinox the sun does not illuminate the western slopes of the Blue Ridge within the purview of a hawkwatcher at Harvey's Knob. Therefore no thermal soaring hawks. That doesn't mean that the hawkwatcher at Harvey's will not see hawks but it does mean that the hawks will be very hard to find as the solar induced thermal will be out over the Great Valley rather than close to the site.
For spotting thermal soaring hawks after the Autumnal Equinox it is recommended that a hawkwatch be established at the Woodpecker Ridge Nature Center. The Woodpecker Ridge Nature Center is located out in the Great Valley where solar induced thermals will abound after the Autumnal Equinox, bringing the thermal soaring hawks into view.

Ridge lift soaring hawks will still be in view but in converse to Harvey's Knob they will be hard to spot. I have witnessed each of these conditions for counting the most hawks migrating through our area and I am convinced that a hawkwatch should be established at the Woodpecker Ridge Nature Center, especially after the Autumnal Equinox. I cannot convey the joys of hawkwatching at Woodpecker Ridge but I can say that looking down on the back of a Merlin from the platform was an experience embedded in my memory.

Dave Holt