Effect of preventive coyote hunting on sheep losses to coyote predation

Aerial hunting is commonly used by agriculture agencies in the Intermountai n West to reduce coyote (Canis latrans) predation on domestic sheep, We ass essed the effect of aerial hunting of coyotes on sheep losses to coyotes, a nd the need for corrective predation management (hours of work, device nigh ts) on the same pastures when sheep arrived for the subsequent summer grazi ng season (3-6 months after aerial hunting). Comparisons were made between paired pastures with (treated) and without (untreated) winter aerial huntin g from helicopters. Average ((x) over bar +/- SE) pasture size was 45.2 +/- 14.1 km(2) (n = 21) for treated pastures and 30.9 +/- 4.6 km(2) (n = 21) f or untreated pastures. There was an average of 1,098 +/- 88 ewes and 1,226 +/- 149 lambs in treated pastures, and 1,002 +/- 149 ewes and 1,236 +/- 79 lambs in untreated pastures. The number of dead lambs located and confirmed killed by coyotes (confirmed kills) was less in treated pastures (2.7 +/- 0.6) than in untreated pastures (7.3 +/- 1.6; P = 0.01). To estimate total lamb losses to coyotes, we multiplied the proportion of known lamb deaths t hat were confirmed coyote kills by the number of missing lambs and added th e resulting figure to the number of confirmed kills. These estimates of lam b loss to coyotes were also lower in treated (11.8 +/- 6.2) than untreated pastures (35.2 +/- 8.1: P = 0.02). Hours required for summer coyote control also were less (P = 0.01) in treated pastures (37.3 +/- 8.5) than in untre ated pastures (57.2 +/- 11.3). Winter aerial hunting increased the mean num ber of coyotes killed annually per pasture fi om 2.0 +/- 1.0 to 5.7 +/- 1.1 (P = 0.04), but it did not affect the number of coyotes removed during sum mer coyote control (P = 0.52). Based on 1995 values for Utah lambs and labo r, winter aerial hunting of coyotes had a benefit:cost ratio of 2.1:1.