Potential risks to ring-necked pheasants in California agricultural areas using zinc phosphide

Abstract

Both wild-caught (32) and pen-reared (29) ring-necked pheasants ( Phasianus colchicus) were studied using radio-telemetry in agricultural areas including: milo (sorghum — Sorghum vulgare), rice ( Oryza sativa), corn ( Zea mays), alfalfa ( Medicago sativa), melon ( Cucumis melo), and weeds. Following capture, demographic data collection, and radio-collaring, they were released into agricultural habitats near Meridian and Nicolaus, CA. After 7 days of acclimation, habitat use and mortality of radio-collared birds were monitored daily using radio-telemetry with Global Positioning Satellites units to record their locations. Randomly selected Meridian alfalfa fields (≈160 acres) were treated with 2% zinc phosphide (Zn 3P 2) on steamed rolled oat (SRO) baits for vole control, whereas, Nicolaus alfalfa fields (≈160 acres) were treated with placebo baits. After ≈5 weeks of radio-tracking during September and October 1996, no pheasants were killed as a result of the Zn 3P 2 baiting. Baits lost substantial potency (>30%) during their exposure to field conditions after 24 h. Most pheasants died from avian or mammalian predation ( n=34, 85%) with pen-reared pheasants more vulnerable to predation than wild pheasants. All mortalities were found in habitats other than alfalfa; upon dissection, they did not have SRO baits (either control or treated) in their gastrointestinal tracts.