The Editor’s Choice article for issue 55:6 is Broad‐scale occurrence of a subsidized avian predator: Reducing impacts of ravens on sage‐grouse and other sensitive prey by O’Neil et al. Associate Editor Margaret Stanley explains the importance of this paper and the disentanglement of natural and anthropogenic influences.

1024px-Centrocercus_urophasianus_-USA_-male-8As a researcher who often fixates on invasive predators, the tricky issues associated with natural predation, from native predators that are part of the system, is a bit of a far-off dream. If only our native predators in New Zealand were abundant enough to start causing trouble….

However, clearly there are many countries and global ecosystems where this management paradox exists – sensitive prey species are in trouble, but one of the key threatening processes is a native predator. There are a suite of generalist predator species that are increasingly benefitting from anthropogenic sources of food or habitat, resources that would not have been available to them without human influences (i.e. anthropogenic subsidies). These subsidies allow predators to increase their population abundance, while at the same time altering their dietary preferences, behaviour and movement, and in some contexts this may lead to cascading effects on prey that are not well-adapted to environmental change.

In the latest Editor’s Choice article, O’Neil et al. have examined such a case. Ecological communities in the semi-arid western U.S, are undergoing a transformation, partly in response to the increase in anthropogenic water and food subsidies. The common raven (Corvus corax), a generalist avian predator, has greatly increased its abundance in response to these subsidies, and has been able to occupy previously unsuitable areas within its range. One of the unfortunate casualties in this community has been the greater sage-grouse (Centrocercus urophasianus), a species of high conservation concern. Although habitat loss and other factors have been responsible for the sage-grouse’s decline, there is growing evidence that nest predation by ravens is hindering sage-grouse reproduction.

55_6 Common_raves_landfill - William I. Boarman, United States Geological Survey
Predators, such as the common raven have increased in number, partly due to water and food subsidies originating with humans. Photo by William L. Boarman.

O’Neil et al. have used an innovative approach to using Bayesian hierarchical occupancy models to not only quantify raven occurrence across the landscape, but to also disentangle the complex relationships between anthropogenic and natural factors that are influencing raven population growth. The authors have used the models to separate and map the natural and anthropogenic influences on occupancy. With anthropogenic influences more amenable to management, this approach lends itself to management actions to reduce raven impacts, such as reducing raven access to resources in sage-grouse concentration areas. The mapping will help with spatial prioritisation of actions, such as removal of roadkill and garbage containment in certain areas.

The novel modelling and mapping approach that separates natural and anthropogenic influences should be of interest to many other researchers and conservation managers, not just those working on predators. It is broadly applicable where widespread survey data are available.

In addition to all this, O’Neil et al. have made all maps fully accessible through USGS ScienceBase Catalog for land and wildlife managers to use in GIS to aid decision-making.

The full Editor’s Choice article, Broad‐scale occurrence of a subsidized avian predator: Reducing impacts of ravens on sage‐grouse and other sensitive prey, is free to read in Volume 55, Issue 6 of Journal Of Applied Ecology