Evaluating the sterile male method on Red-winged Blackbirds: clinical evaluation of thiotepa as a sterilant

Before attempting a small-scale field trial of the sterile male method to reduce blackbird population levels, laboratory studies were undertaken, in 1978 and 1979, to evaluate the efficiency of thiotepa as a bird sterilant. The LD50 of thiotepa was determined (6.2 mg/kg of body weight), as well as the applicable dose to produce sterility (4.32 mg/kg of body weight) without causing mortality, following a treatment beginning on April 25, 1979. This dose inhibited testicular growth for about 1 month. During this period, testes weight of treated redwings was only 10% of normal weight. Identical doses to those administered to male redwings produced the same effects on testicular development of grackles and cowbirds. No effects were noted on the testes weight of male Red-winged Blackbirds 1 year after treatment with thiotepa. Results indicated that the sterile male approach may have potential to reduce blackbird populations causing crop damage.