Toxicity of DRC-1339 to Starlings

Abstract

Reduction of starling (Sturnus vulgaris) populations by the use of poisoned baits is frequently suggested, but an effective, nonhazardous toxicant has not been available. A recently discovered chemiical, DRC-1339 (3-chloro-p-toluidine hydrochloride), meets many of the requirements; it is highly toxic to starlings (acute oral LD50o = 3.8 mg/kg), well accepted, relatively nontoxic to rats, and generally less toxic to most other birds. Hawks are particularly resistant and there appears to be little danger that these birds, or mammalian carnivores, would be killed by eating DRC-1339-poisoned starlings. The margin of safety is less for the game birds that were tested. DRC-1339 causes a slow, nonviolent death; uremic poisoning and congestion of major organs appear to be the principal causes. Starlings have become a serious agricultural problem in the United States since their introduction from Europe in 1890. In recent years they have caused considerable losses at livestock and poultry feedlots, particularly in the intermountain region of the West. Reductional control using poisoned bait is frequently proposed as a solution to the starling problem, but a suitable toxicant has been lacking. The Denver Wildlife Research Center has been searching for such a compound since 1961 and has tested more than 400 chemicals. These were solicited from chemical companies, selections usually based on indicated toxicities to other species of birds or structural similarity to compounds previously tested that showed promise as a starling toxicant. Chemicals with the following characteristics were sought: 1. High toxicity to starlings. 2. Low toxicity to mammals, thus minimizing the possibility of accidental poisoning to man or livestock other than poultry. 3. Little aversion by starlings to treated baits. 4. A slow, nonviolent death, which would eliminate bait avoidance caused by birds displaying symptoms or dying at the baiting site. 5. Minimum hazards to avian and mammalian predators that might eat poisoned birds. Of the chemicals tested, only one-3-' chloro-p-toluidine hydrochloride, coded by us as DRC-1339--met these requirements. The purpose of this paper is to describe some of the toxicological characteristics of DRC-1339 to starlings and other birds. We acknowledge the valuable contributions by co-workers at the Denver Wildlife Research Center, principally J. F. Besser 1 Thomas J. DeCino performed much of the research herein reported before his untimely death November 19, 1964. This paper was prepared by the junior authors.