title: An index technique to monitor broadcast calibration and bait pick up, plus rodent and avian sign under arid conditions.
abstract: As part of product-performance and wildlife-hazards studies of 2% zinc phosphide (Zn3P2) steam-rolled-oat baits (11.2 kg ha-1) to reduce vole populations (Microtus spp) in alfalfa (Medicago sativa), we used randomly located, brushed-dirt plots (eight approximately 930-cm2 plots per 0.2-ha enclosure) to monitor bait-broadcast and -removal patterns, as well as to index vole and avian sign. Research was conducted in 18 x 0.2-ha enclosures containing 2.5-year-old stands of alfalfa; a 2-day pre-bait (placebo baits broadcast in all enclosures) period followed by a 14-day test-bait period (placebo and 2% Zn3P2 baits in nine enclosures each) characterized the bait exposures. Baits were broadcast manually by two certified pesticide applicators (CPAs) using Spyker Model-75 spreaders. Baits that fell onto plots were counted < 30 min later to assess the uniformity of bait distribution. The main statistical design was a 2 (placebo or Zn3P2 baits) x 3 (vole-only, vole-pheasant, vole-quail exposures) x 14 (days) factorial, with days considered repeated measurements. In the six vole-only enclosures, baits were removed from the brushed-dirt plots and replaced with four 0% or 2% Zn3P2 baits (one per 232.6-cm2 quadrant; 32 per enclosure); these 'placed' baits were then monitored daily for removal, while the surfaces of all plots were monitored daily for the presence:absence of animal/bird sign. Key results were: (a) 3.51 (+/- 2.66) and 3.39 (+/- 3.52) mean (+/- SD) baits were found on plots after pre-bait and test-bait broadcasts, respectively--less than the predicted 4.52 particles per 930-cm2 plot; (b) baits 'placed' on plots in placebo-baited enclosures were removed earlier than those in Zn3P2-baited enclosures--data in agreement with observed vole mortality; and (c) species x bait interactions occurred for both the vole- and pheasant-sign counts, but not quail-sign counts--data also indirectly confirming Zn3P2-induced mortality effects on voles and pheasants. This technique has utility for a variety of wildlife biology and chemical registration studies; although limited to arid conditions, the technique affords useful indices of broadcast calibration, bait pick-up, as well as target and non-target species mortality.
authors.affiliation: USDA/APHIS/WS, National Wildlife Research Center, 4101 LaPorte Avenue, Fort Collins, CO 80521-2154, USA. ray.t.sterner@aphis.usda.gov
authors.forename: Ray T
authors.initials: RT
authors.lastname: Sterner
authors.forename: Craig A
authors.initials: CA
authors.lastname: Ramey
mesh_terms: D000818:Animals; D000835:Animals, Wild / Q000502:physiology*; D003411:Arvicolinae / Q000502:physiology; D001717:Birds / Q000502:physiology*; D003889:Desert Climate; D010720:Phosphines / Q000633:toxicity*; D011784:Quail / Q000502:physiology; D012375:Rodent Control / Q000379:methods / Q000706:statistics & numerical data; D012377:Rodentia / Q000502:physiology*; D012378:Rodenticides / Q000633:toxicity*; D017967:Zinc Compounds / Q000633:toxicity*
chemical_list: D010720:Phosphines; D012378:Rodenticides; D017967:Zinc Compounds; C009701:zinc phosphide