Buffer-zone distances to protect foraging and loafing waterbirds from disturbance by personal watercraft and outboard-powered boats

Outdoor recreation and ecotourism can have negative effects on wildlife species, so it is important to determine buffer zones within which activities near critical wildlife areas are limited. We exposed 23 species of waterbirds (Pelecaniformes, Ciconiiformes, Falconiformes, Charadriiformes) to the direct approach of a personal watercraft (PWC) and all outboard-powered boat to determine their flush distances. We used 11 sites with a mixture of low, moderate, and high amounts of human activity along the east and west coasts of Florida during September-November 1998 and April-June 1999. We detected considerable variation In flush distances among individuals within the same species and among species in response to both types of vessels. Average flush distances for the PWC ranged from 19.5 m (Least Tern [Sterna antillarum]) to 49.5 m (Osprey [Pandion haliaetus]), whereas average flush distances for the outboard-powered boat ranged from 23.4 m (Forster's Tern [S. forsteri]) to 57.9 in (Osprey). Larger species generally exhibited greater average flush distances for both types of watercraft. A comparison of the flush distances elicited by each watercraft indicated that only the Great Blue Heron (Ardea herodias) exhibited significantly larger flush distances (t test, p<0.01) in response to the approach of the PWC than in response to the outboard, whereas four species (Anhinga [Anhinga anhinga], Little Blue Heron [Egretta caerulea], Willet [Catoptrophorus semipalmatus], and Osprey) exhibited significantly larger flush distances (t test, p<0.05) in response to the approach of the outboard-powered boat than In response to the PWC. Eleven species (68.8%) showed no significant difference (t test p>0.05) in their flush distances in response to the fast-moving PWC and the outboard-powered boat. Our data suggest that a single buffer-zone distance can be developed for both PWC and outboard-powered vessels. Buffer zones of 180 in for wading birds, 140 in for terns and gulls, 100 in for Plovers and sandpipers, and 150 in for ospreys would minimize their disturbance at foraging and loafing sites in Florida.