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<br />its upwind border, which would tend to promote the growth of clouds. In the <br />case of a windfarm located on a forested coastline, local convergence occurs <br />naturally and would be only slightly increased by the windfarm, At any rate, <br />this effect is expected to be so small as to be very difficult to verify, <br /> <br />Throughout the region projected for windfarm sites, both normal <br />climatic changes and terrain-related microclimatic gradients are greater than <br />. the microclimatic effects expected of windfarms by ten to perhaps a hundred <br />times or more, No significant impact from the windfarms is to be anticipated. <br /> <br />b, Wildlife. - The types of wildlife considered in assessing the <br />impact of large windfarms are large mammals and birds, Other wildlife, <br />including small mammals, reptiles, and insects, would be likely to undergo <br />temporary disturbance or displacement during the construction phase, with <br />their habitat returning to its previous condition in all major aspects <br />thereafter, provided that proper measures were taken to minimize disturbance <br />during construction and clean up after it. <br /> <br />As a framework for analyzing the impact of land-use changes on <br />animals, a workshop group of animal biologists has adopted "indicator species" <br />selected as typical of a class of animal/habitat relationships t?. Further <br />study would be required those of species that would be seriously disturbed by <br />windfarms and the activity that would be associated with them, and those that <br />would tolerate such disturbance without danger to the species. <br /> <br />Three classes of birds may be considered: birds that: nest in the <br />area, birds that migrate through the area, and birds of prey, Birds that nest <br />in the area are primarily affected by changes in food supply and sheltl~r or <br />nesting sites. Since windfarm use would not affect these primary elements, <br />and since these birds seldom fly high enough to be in conflict wi.th the moving <br />blades of windpowered generators, and are in an alert state in which evasive <br />action is normal, no considerable impact is to be expected, 16. <br /> <br />For migrating birds, the situation is quite different. They normally <br />fly at heights more than 200 m above the ground and do not take 'iring against <br />adverse winds, low clouds, or greatly reduced visibility. However, once <br />launched, they seem to enter a state of decreased alertness and will often <br />continue flight even if overtaken by adverse ,.reather, which may blow them <br />off course, bring them closer to the ground, and make it more difficult for <br />them to avoid obstructions. A storm that strikes a migrating flock might <br />therefore force it into the range of a windfarm, There have been occasional <br />reports of bird kills 'at television antenna farms numbering in the tens of <br />thousands in a single night under adverse weather (W. Spofford, personal <br />communication, 1978), Guy wires seem to be especially hazardous, Migrants <br />crossing windfarms under these conditions would be significantly at risk. <br /> <br />On t:he basis of the volume swept by the moving blade of a wind <br />machine and the time that a passing bird would remain within the swept <br />volume, it has been calculated that one bird in eiEht moving at 3,5 mis, or <br />one bird in 17 moving at 8 m/s, would be struck 13. (Since migrants fly <br />downwind, the appropriate speed would be the sum of windspeed and flight <br />speed.) However, comparisons with observation suggest that this simplistic <br />model grossly overpredicts bird kills and its usefulness is seriously <br />doubtful. <br />