Can camera trapping help capture predator ecology?

Over the last few centuries, Scotland has been a dangerous place to be a predator. Described by some as the Scottish wildlife clearances, land managers killed incredible numbers of predatory animals to protect sheep and game – driving many predators to extinction. Sadly, there is abundant evidence that remaining predators are still subject to persecution over parts of the Highlands.

Predators were once common throughout Scotland as part of a diverse and dynamic ecosystem. Photo credit: Scotland Big Picture.

Things are changing, though, and in one particular area of the Cairngorms National Park – encompassed by the Cairngorms Connect partnership – something remarkable is happening. The carnivores are returning and, contrary to traditional wisdom, it appears that populations of prey species are not being eradicated by this predator proliferation. A natural, diverse predator-prey system is coming to life, and to study this fascinating situation, the Cairngorms Connect Predator Project (CCPP) has been set up. This project is supported by funding from the Endangered Landscapes Programme and aims to find out how predators and prey coexist, and how predator species interact (for example – do predators eat other predators?). 

Predator populations have increased dramatically in this persecution-free haven. Jays and goshawks have become well established in the area. Pine martens and foxes have increased and, according to various accounts, badger numbers have increased considerably. Golden eagles have reached their highest density in living memory and the first pair of white-tailed eagles is nesting successfully. Sightings of eight other species of breeding raptor, including hen harriers, buzzards, peregrine and merlin, as well as ravens, carrion and hooded crows are common. Add to this a range of other mammalian predators, including stoats and weasels, and it’s easy to understand why some people predicted the demise of vulnerable prey species like capercaillie and black grouse.

However, to the surprise of many, the capercaillie population in parts of the Cairngorms Connect area has increased during the last 15 years; the black grouse population has remained roughly stable; and the red squirrel, another prey species that is threatened in Scotland, is still abundant. All this despite the fact that the number of predators has increased dramatically. How is this possible?

Despite a comeback in predators, capercaillie populations are on the rise. Photo credit: Peter Cairns.

Studies so far by the CCPP indicate that, for example, goshawks eat only a tiny number of black grouse, and only one hen capercaillie has been identified in end-of-season nest checks. They are, however, eating jays and other crows, which are known to depredate the nests of grouse species. Could the presence of goshawks be a net benefit to woodland grouse?

Traditional diet analysis – teasing apart scats in the lab and identifying hair and bones – by Cristian Navarro, a CCPP-funded PhD student, has revealed that the diet of martens and foxes comprises mainly of field voles, rather than rarer prey species. Cristian is now investigating the diet of foxes, martens and badgers, using the latest genetic techniques. This will reveal all of the prey species contained within over 1000 scats! He also has 6000 camera-trap-nights worth of data that will elucidate the spatial relationships of these mammals. A parallel study, led by Forestry and Land Scotland, is looking at the utilization of deer grallochs by predators. The ultimate aim is to find out if this additional and easy-to-find food source supports an unnaturally high population of predators, or if it diverts predators from eating endangered prey species.

The camera traps set by PhD student Cristian Navarro are revealing a fascinating insight into predator ecology in the Cairngorms Connect project area. Photo credit: Cristian Navarro.

The return of predators to the Cairngorms Connect area is reassuring and provides a vision how biodiverse Scotland could be, not only in terms of the number of predator species, but also because of the diversity of ecological processes and interactions that are occurring. These phenomena are the very essence of biodiversity, with profound benefits for us all. A life time of study by ten people would not answer all of the questions that are arising, but the Cairngorms Connect Predator Project team has made a start.

This article is reproduced with kind permission from its author Kenny Kortland. Kenny is a Wildlife Ecologist at Forestry & Land Scotland, who are a partner of the Cairngorms Connect project.