Abstract
Results of several herring gull (Larus argentatus) control programs using DRC-1339 (3-chloro-4-methyl-benzenamine hydrochloride) suggested that the published median lethal dose (LD50) of 2.9 mg of DRC-1339/kg of body weight may not be accurate in some environments. We conducted laboratory trials to estimate LD50 values of DRC-1339 and of alpha-chloralose (AC) for herring gulls inhabiting fresh water. We also conducted field trials to compare effectiveness of these compounds in simulated gull control operations. We calculated the LD50 for DRC-1339 as 4.6 mg/kg and 43.1 mg/kg for AC. Mean (+/-SD) time to death for DRC-1339-dosed birds varied from 34.0 (+/- 12.2) hours at LD96 to 109.5 (+/-55.5) hours at LD27 AC time to death varied from 2.3 (+/-0.5) hours at >LD99 to 5.8 (+/-0.0) hours at LD13. In field trials, DRC-1339 baits treated at 27.4 mg/kg (LD99) resulted in 29% known mortality. In contrast, AC baits with a 30-mg/kg dosage (<LD01) resulted in 50% capture success and no mortality. AC baits at 58 mg/kg (LD99) resulted in 89% capture success and 41% mortality. With AC baits at 95 mg/kg (>LD99), 65% of gulls were captured with 82% mortality. AC was more effective than DRC-1339 in removing gulls from a nesting colony. We recommend consideration of AC as a gull population management chemical because It is fast-acting, humane, and can be used as a nonlethal capture agent.