Bohrer, G., Brandes, D., Mandel, J. T., Bildstein, K. L., Miller, T. A., Lanzone, M., Katzner, T., Maisonneuve, C. & Tremblay, J. A. 2012 Estimating updraft velocity components over large spatial scales: contrasting migration strategies of golden eagles and turkey vultures. Ecology Letters 15, 96-103 DOI: 10.1111/j.1461-0248.2011.01713.x Bohrer1 2012 Bohrer1 2012 Supp1 Bohrer1 2012 Supp2
Soaring birds migrate in massive numbers worldwide. These migrations are complex and dynamic phenomena, strongly influenced by meteorological conditions that produce thermal and orographic uplift as the birds traverse the landscape. Herein we report on how methods were developed to estimate the strength of thermal and orographic uplift using publicly available digital weather and topography datasets at continental scale. We apply these methods to contrast flight strategies of two morphologically similar but behaviourally different species: golden eagle, Aquila chrysaetos, and turkey vulture, Cathartes aura, during autumn migration across eastern North America tracked using GPS tags. We show that turkey vultures nearly exclusively used thermal lift, whereas golden eagles primarily use orographic lift during migration. It has not been shown previously that migration tracks are affected by species-specific specialisation to a particular uplift mode. The methods introduced herein to estimate uplift components and test for differences in weather use can be applied to study movement of any soaring species.
23 tows by Tom and Hal. [Note: last January SVS had 6 tows for the entire month!]
Saturday was quite windy, but resulted in the majority of the weekend’s tows. Some flights were able to find spotty lift and all who flew gained experience in turbulent air and crosswind takeoffs and landings.
Sunday was clear and balmy with very light and variable winds.
_19 tows by Larry, Graham & Tom. The forecast winds were tolerated very well, but the cold dampened enthusiasm as the weekend progressed. Saturday started out balmy, Sunday was windy and cold, with rain showers in the late afternoon. Monday was just plain cold and windy!
One flight captured wave on Saturday to 12k+, and terminated for lack of oxygen equipment. A solo student stayed up almost 2 hours on both Saturday and Monday.
Always lots of fun no matter the weather!
REMEMBER: all members are welcomed to attend the quarterly board meeting on Friday at 7:00 p.m. at Tom Belt’s Fontana Clubhouse in Charlottesville. (SECRET: several members usually dine in splendor at the local McDonalds just before the meetings).