Raptors benefit from biosolids applications on rangelands

Abstract

Globally, many grasslands have been lost or degraded via settlement, conversion to agriculture, or use as pasture. These losses have damaged the ability of migratory and nomadic birds of prey to find suitable breeding territories. Habitat restoration of degraded grasslands via the application of biosolids, the treated and sterilized remains from sewage treatment plants, improves soil water retention and nutrient profile, leading to substantial gains in plant growth and nutritive quality. Gains to wild and domestic herbivores have been documented, but impacts to predators are poorly known. Here, we test the hypothesis that biosolids-applied pastures are attractive to and support migratory and nomadic avian predators in central British Columbia, Canada. We obtained habitat records from sightings and prey remains from pellets for three vole-specialists, Long-eared Owls (Asio otus), Short-eared Owls (A. flammeus), and Northern Harriers (Circus hudsonius), as well as the generalist American Kestrels (Falco sparverius). During 5 years, the three diurnal species preferentially used biosolids-applied pastures, and kestrels and owls nested in biosolids-applied pastures or in forest patches adjacent to these pastures. Grasshoppers were more abundant on pastures with biosolids and were common prey for American Kestrels. The owls and harriers preferentially consumed voles, although Short-eared Owls consumed deermice (Peromyscus maniculatus) as a major additional food source during years when voles were scarce. Long-eared Owls were documented only in the 2 years when voles were common. Collectively, these results suggest that biosolids-amended landscapes may attract raptors, even when vole densities are low.

Keywords

• american kestrel
• biosolids
• diet
• grasslands
• habitat
• long-eared owl
• northern harrier
• restoration
• short-eared owl