Artichoke growers in Monterey County, California currently use a fresh artichoke bract chlorophacinone bait to control their primary vertebrate pest, the California meadow vole. Upon suspected chlorophacinone resistance by meadow voles in artichoke fields, an alternative has been sought. We studied the effect of zinc phosphide-treated artichoke bracts on California meadow voles. We found that zinc phosphide-treated artichoke bracts were effective in reducing meadow vole populations on treated plots by 95-98%. Our results suggest that zinc phosphide-treated artichoke bracts are effective in reducing California meadow vole populations in artichoke fields and may provide a useful alternative for areas in which anticoagulant resistance by voles is suspected.

The California meadow vole, Microtus californicus, is a major vertebrate pest in artichoke fields of Castroville, California. Complaints from growers about the effectiveness of the only available rodenticide, chlorophacinone treated artichoke bracts, led researchers to the test the bait and baiting strategies. When laboratory trials were conducted in 2001, the poor dose-response correlation and apparent low sensitivity to chlorophacinone in some animals suggested the possibility of anticoagulant resistance. The current study was initiated to examine potential resistant of voles from artichoke fields in the Castroville area. Baseline blood coagulation data were obtained from wild, anticoagulant-susceptible voles trapped in Yolo County, California and compared to data from Castroville voles. Results indicate a significant difference in clotting times 24 hours after dosing with anticoagulant between voles from Castroville artichoke fields and voles from the Yolo population. This supports the hypothesis that voles from Castroville artichoke fields are resistant to anticoagulants.

The Office of Spill Prevention and Response (OSPR) oversees clean-up, natural resource damage assessment activities, and wildlife protection activities at oil spills in California. OSPR contracted with the University of California, Davis (UCD) in July 2000 to establish the Hazing Group (HG) with the goal of preventing birds from becoming exposed in the event of a spill. OSPR activated HG for 2 oil spills in 2004 and 2005. In the Suisun Slough Pipeline Spill near Fairfield on 27 April 2004, a pipeline break released 3 ´ 105.5 L of diesel fuel into a 98-ha freshwater marsh. HG was activated and arrived on scene on 29 April. HG deployed propane cannons and bamboo stakes with mylar along oiled channels, patrolled on foot or by canoe, and fired pyrotechnics at 16 species of birds. Most birds responded favorably and left the marsh or continued on without landing. CAPA rockets and shell crackers were most effective. Hazing continued for 21 days. Post-spill evaluation indicated pre-spill efforts to improve preparedness and response time were effective, but the absence of an assigned vehicle and the location of the primary HG responder away from UCD at the time of call-out increased response time. In the Pyramid Lake Spill near Santa Clarita on 23 March 2005, a pipeline break released 4.8 ´ 106 L of crude oil, which flowed down a creek into Pyramid Lake. HG was activated on 29 March and arrived on-scene on 30 March. HG activities were limited to reconnaissance; few birds were observed on the lake. High winds and rough waters prevented boat operations and were also problematic for shore-based hazing. With the spill contained to a limited area, low bird numbers present, and unfavorable weather forecast to continue, initiation of hazing would have been difficult and of limited benefit. HG was dismissed from the spill response on 31 March. Post-spill evaluation indicated response time was excellent, aided in part by an assigned vehicle. Weather limited hazing, and the location of Pyramid Lake and the timing of the spill was fortuitous with regard to low bird numbers present. On 13 January 2005, oiled birds appeared along the southern California coast between Santa Barbara and Venice. Over 1,400 oiled birds were recovered within 8 days, and up to 5,000 birds may have been oiled along 129 km of coastline. The source of this spill, called the Ventura County Oiled Bird Incident, was unknown. Wildlife officials did not find a major slick on the water. HG was not activated for this spill because there was no identifiable slick or contaminated area to haze birds away from, the impacted area was large, and the impacted species, mostly grebes, are not easily hazed. Guidelines for activation of HG are suggested that take into account the species at risk, the responsiveness of the species to hazing, presence of identifiable source, slick, or contaminated area, imminent likelihood of clean areas becoming oiled, presence of clean areas for hazed birds, the size or extent of the spill, and weather conditions.