Isotopic analysis reveals landscape patterns in the diet of a subsidized predator, the common raven

Abstract

1. Anthropogenic subsidies to native predators can have cascading effects on sensitive prey populations, but the spatial mechanisms behind these effects are often unknown.2. We used a stable isotope mixing model to reconstruct spatially naïve assimilated diets of common raven (Corvus corax) chicks and then used regression analysis to investigate landscape patterns in assimilated chick diet, with particular respect to the eggs and chicks of greater sage-grouse (Centrocercus urophasianus).3. Assimilated raven diets were primarily composed of mammal carrion, followed by anthropogenic food and sage-grouse eggs and chicks. 4. Raven diets showed landscape gradients, whereby raven chicks in nests near active greater sage-grouse breeding leks consumed a higher proportion of sage-grouse eggs, sage-grouse chicks and insects in their diet and less mammal carrion. A majority of raven nests on anthropogenic nesting structures (78.7%) were within 5 km of the nearest sage-grouse lek. Ravens nesting in high-probability greater sage-grouse nesting habitat consumed more insects and plants and less mammal carrion.5. In landscapes devoid of natural raven nesting substrates, such as our study area, anthropogenic nesting substrates can 'anchor' breeding ravens nearer to greater sage-grouse leks, with concomitant increases in raven predation on greater sagegrouse nests. Curtailment of anthropogenic nesting substrates within 5 km of a sage-grouse lek may have a disproportionately positive impact on sage-grouse populations. More generally, these findings highlight that the spatial arrangement of anthropogenic subsidies can result in indirect interactions between humans and predators with direct implications for predators and prey.

A spatially explicit modeling framework to guide management of subsidized avian predator densities

“…Predictions were obtained from a Bayesian hierarchical distance sampling model of common raven densities within southwestern Great Basin sagebrush ecosystems, USA. transmission lines (Coates et al, 2014;Harju et al, 2018;Harju, Olson, et al, 2021;Howe et al, 2014;O'Neil et al, 2018). In our study, raven densities varied widely in response to landscape features associated with agricultural crops, pastures, and roads at low elevations.…”

“…The potential for anthropogenic resource subsidies has been previously tied to spatial variation in raven distributions within sagebrush ecosystems. For example, spatial pattern in raven presence has been associated with anthropogenic development and human activity (Bui et al, 2010; Coates et al, 2020; Harju et al, 2018; Kristan & Boarman, 2003, 2007), road density (Coates et al, 2020; O'Neil et al, 2018), presence of agricultural land and livestock (Coates et al, 2020; Coates, Brussee, et al, 2016), artificial point sources for water or food (Boarman et al, 2006; Harju et al, 2018; Kristan & Boarman, 2003, 2007), and tall structures such as transmission lines (Coates et al, 2014; Harju et al, 2018; Harju, Olson, et al, 2021; Howe et al, 2014; O'Neil et al, 2018). In our study, raven densities varied widely in response to landscape features associated with agricultural crops, pastures, and roads at low elevations.…”

Stress response of fire salamander larvae differs between habitat types

“…Individuals of the same species often reside in different habitats, which can come with different selection pressures. For instance, the common raven ( Corvus corax ) inhabits different habitat types and adapts its diet to food resources available in each type of habitat [ 1 ]. Other species show adaptive morphological changes in response to different habitats such as the Mexican tetra ( Astyanax mexicanus ) [ 2 ].…”