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.

We studied how human use of trails affected foraging shorebirds over 24 months at 3 locations around San Francisco Bay, California, USA. By observing sites with trails and nearby sites without trails, we assessed whether numbers of trail users had an effect on the number of birds, species richness, or proportion of shorebirds foraging on tidal mudflats. Human use at non‐trail sites averaged <1 person/hour, whereas use at trail sites averaged 68 people/hour. Despite these differences, we found no negative effects of trail use on the number of birds, species richness, or proportion of birds foraging, either overall or by season, when comparing trail to non‐trail sites. Human use of trail sites on higher use days (typically weekends) averaged about 2.5 times the level on lower use days (typically weekdays). When comparing bird response on paired lower and higher use days at the trail sites, we found the number of shorebirds decreased with increasing trail use (F1,119 = 4.20, P = 0.043), with higher trail‐use days averaging 25% fewer birds than on lower use days. Although managers may allow human use of trails adjacent to shorebird foraging areas under some conditions, high levels of trail use may negatively affect birds, making it essential to offer birds alternative, trail‐free foraging opportunities.

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