Burrowing owls and agricultural pesticides: Evaluation of residues and risks for three populations in California, USA

Abstract

We examined selenium, organophosphorus, and organochlorine pesticide residues in egg, footwash, and feather samples from burrowing owls in three populations in central and southern California. Eggs from all sites contained detectable levels of p,p′‐dichlorodiphenyldichloroethylene, with the San Joaquin Valley site containing up to 33 μg/g (geometric mean x¯ = 7.52). Only low levels of polychlorinated biphenyls were detected, however (geometric mean x¯ = 1.98, n = 2). Selenuim concentrations were low in all samples (geometric mean x¯ = 0.426, n = 20). Eggshells collected in 1996 were 22% thinner than eggs collected prior to 1937. In addition, feather samples contained low levels of dichlorodiphenyldichloroethylene, and footwash samples indicated exposure to the pesticide chlorpyrifos. Pesticide‐use records indicated that one population might also be at risk from applications of aldicarb near nests during the breeding season.

The Diet of Western Burrowing Owls in an Urban Landscape

“…For example, in the agricultural Imperial Valley, Rosenberg and Haley (2004) reported that these 3 orders were the most frequent prey found in pellets. In Oregon and Washington sagebrush/disturbed grasslands (Green et al 1993) and central California grasslands (Gervais et al 2000), Coleoptera and Orthoptera were also prevalent species in pellets, as were spiders (Araneae). As in many other studies of Western Burrowing Owls (Gervais et al 2000, Moulton et al 2005, Hall et al 2009), rodents were a major part of the owls' diets in Santa Clara County, composing over 70% of the biomass consumed.…”

“…In Oregon and Washington sagebrush/disturbed grasslands (Green et al 1993) and central California grasslands (Gervais et al 2000), Coleoptera and Orthoptera were also prevalent species in pellets, as were spiders (Araneae). As in many other studies of Western Burrowing Owls (Gervais et al 2000, Moulton et al 2005, Hall et al 2009), rodents were a major part of the owls' diets in Santa Clara County, composing over 70% of the biomass consumed. Rodents were important year-round (although less so in the winter nonbreeding season) for owls living on both park or nonpark land.…”

“…In particular, Botta's pocket gopher was a major component of owl diets in our study area in terms of percent biomass per burrow, both year-round and in different landuse types. This widely distributed rodent species has been recorded in numerous studies, but not often as a major dietary component for Western Burrowing Owls (Coulombe 1971, Thomson 1971, Rosenberg and Haley 2004, Hall et al 2009; but see Gervais et al 2000). Outside the range of T. bottae, T. talpoides (northern pocket gopher) appears as an important prey item for Burrowing Owls in sagebrush habitats in Idaho (Gleason and Johnson 1985) and in Oregon and Washington (Green et al 1993).…”

“…In both agricultural areas (Gervais et al 2000, Moulton et al 2005) and sagebrush/grassland habitats in Colorado (Plumpton and Lutz 1993), Montana (Restani et al 2001), and Idaho (Moulton et al 2005), these rodent taxa were major components of owls' diets. In Santa Clara County, Microtus californicus and Mus musculus were the other large components of the rodent biomass in owl diets; both are abundant species that regularly inhabit human-altered environments.…”

The diet of the Burrowing Owl, Athene cunicularia, in the arid lands of northeastern Patagonia, Argentina

“…Its foods habits have been studied patchily throughout its range (e.g., Gervais et al, 2000;York et al, 2002). Studies in South America have included mainly Southern Brazil (e.g., Silva-Porto and Cerqueira, 1990), Central Chile (e.g., Jaksic and Marti, 1981;Schlatter et al, 1980;Torres-Contreras et al, 1994;Yan˜ez and Jaksic, 1979;Zunino and Jofre´, 1999), and some Argentinean agroecosystems (e.g., Bellocq, 1987;Bellocq and Kravetz, 1994;Coccia, 1984).…”