The algorithm for calculating effects of convection comes from a 1983 paper by David Goldstein (Effect of wind on avian metabolic rate with particular reference to Gambel's quail; Physiological Zoology 56: 485-492). Goldstein (who I know from my time at UCLA in the late 1970s) complied convection data from several bird species (goldfinches to golden eagles; 13 to 3800 g) and derived an equation that predicted metabolism with high accuracy over a range of temperatures and wind speeds. From his equation, I derived this adjustment to calculated thermoregulatory costs:
cost_{wind} = cost_{no wind} * (1 + b * wind speed^{0.5})
where b = .0092 * mass^{0.66} * (LCT - T_{e})^{0.32}
(mass in grams; wind speed in m/s; LCT is lower critical temperature and T_{e} is environmental temperature, both in °C)