In this post Matthew Hethcoat discusses his recent paper, with Anna Chalfoun ‘Towards a mechanistic understanding of human-induced rapid environmental change: a case study linking energy development, nest predation and predators‘, which is published in Issue 52:6 of Journal of Applied Ecology, out today.
North America’s sagebrush steppe, also known as the big empty, holds a secret. The sparrows, thrashers, and other songbirds that inhabit this vast sagebrush sea are in decline and we’re trying to understand why.
The story of the big empty goes back to the 1800s and can be thought of like a modernist tragedy. Despite being one of the largest ecosystems in the United States, the sagebrush steppe is suffering a death from a thousand cuts. Agricultural conversion, urbanization, invasion of exotic species – all the usual actors were on stage for act one.
The second act opens with the pumpjacks, pipelines, drill pads, and waste pits associated with expanding energy infrastructure. The year is 2008 and the preceding decade has wrought a five-fold increase in natural gas development. Our research group enters stage left.
We wanted to identify any threats oil and gas development might pose to songbirds in Wyoming. Oil and gas deposits underlie approximately one third of North America’s sagebrush steppe, and in Wyoming the overlap is even greater – 70% of petroleum resources occur in sagebrush habitats. Wyoming lists a number of songbirds from the sagebrush system as Species of Greatest Conservation Need, and the expansion of energy development is seen as a major challenge.
Initially, we focused on abundance and species richness. Point counts spanned three energy fields and sampled the birds across a gradient of intensity of energy infrastructure. We found significant declines in songbird abundance in areas with greater energy development, but no change in species richness. The same species were present, just fewer of them.
We wanted to know what might be causing those observed declines in abundance, so next we concentrated on reproductive success. We monitored nests to see if differences in breeding success could be driving the changes in abundances we had observed. Indeed, nest survival rates decreased with increased energy development, suggesting one potential mechanism for the declines in abundance we had seen. But this left us with new questions. Why were nests more likely to fail in areas with more energy development?
The short answer is because something was eating them. Songbird eggs and nestlings are vulnerable to a remarkable array of potential predators. Until the moment a nestling is ready to leave the nest almost anything can, and will, eat them. During our nest monitoring we set up camera units, which recorded day and night continuously, at a subset of active nests to identify predators. These cameras use infra-red illumination, of a wavelength that is invisible to vertebrates, to film at night. Just as we don’t see the beam transmitted to televisions to change the channel, potential nest predators couldn’t see the beam illuminating the nest at night. This allowed us to understand the suite of nest predators we needed to focus on to understand the increases in nest predation we were seeing. Check out some of the predation events we recorded in the video below.
In our newest paper in the Journal of Applied Ecology we think we’re starting to understand what’s going on. We found that rodents (mice, chipmunks, and ground squirrels) were the most important nest predators, accounting for about 75% of predation events. In addition, nest survival rates were negatively correlated with the abundances of these important predators. Simply put, nests situated in areas with more rodent predators were significantly more likely to be eaten.
The process of science, unlike a play, often lacks a denouement. The story of the big empty continues, as we find ourselves asking new questions. Why are we seeing changes in the abundances of rodents with increased energy development activities? What factors are influencing their abundances and habits in energy fields?
Energy development is one of the greatest threats to the sagebrush sea, furthering the habitat loss, fragmentation, and degradation that historically beset its vastness. But swelling energy demands will continue to be a major land-use driver globally. World energy production is forecasted to increase 40% in the next 20 years, with the U.S. anticipated to develop more than 200,000 km2 of new land for energy production. Addressing the challenges imposed by new and emerging sources of anthropogenic disturbance is likely to be the backdrop for a host of dramatic productions in the coming decades. All the world’s a stage.