“…McDonald et al (2000) demonstrated that 84-89% of gamekeepers use rodenticides during the winter and spring (December-May inclusive) compared to 37-45% in summer and autumn (June-November inclusive). We therefore stratified the samples of owls that were analysed so as to eliminate any potential seasonal biases in exposure that might be associated with seasonal variation in use (Table 1) (HPLC) following extraction methods described by (Hunter, 1985) and subsequently modified by Jones, (1996). For each liver sample, approximately 1 g of tissue was weighed, ground to a homogenous paste with furnace-cleaned sand, and mixed with furnace-cleaned anhydrous sodium sulphate to form a free-flowing mixture.…”