Wolves prefer running in straight lines

In this post, Associate Editor Johan du Toit discusses a recent paper ‘Faster and farther: wolf movement on linear features and implications for hunting behaviour’ by Melanie Dickie, Robert Serrouya, Scott McNay and Stan Boutin.

Humans make lines on the landscape

When flying over any landscape, what strikes the eye as the most distinctive evidence of human activity on the ground is linear features in the form of fencelines, electrical transmission lines, pipelines, and so on.  On flat landscapes the roads and railways are mostly straight too.  Modern humans strive for linearity because a straight line is the most efficient way of connecting two points and straight edges allow internal areas to be measured with precision.  A person hiking across country through the boreal forests of North America might not appreciate just how scarred the landscape is by linear features.  But in their study Dickie et al. found that the forestry and energy industries of northeastern Alberta and northwestern Saskatchewan have (so far) created 0.5 – 16 km of linear features in each square kilometer of forest.  Those features, being strips cleared of woody vegetation, are avenues along which large-bodied land animals can move more easily than if they were to weave their way through the trees and bushes in the forest.

Wolves use those lines

It would be reasonable to assume that if wolves can increase their speed and reduce their energetic costs by travelling in straight lines across the landscape then they should become more efficient in encountering prey.  If so, then higher kill rates would be expected and that could be bad news for woodland caribou, which are on a worrisome population trajectory.  And sure enough, after monitoring 22 GPS collars deployed across six wolf packs during 2013-14, Dickie et al. found that wolves far prefer travelling along linear features than through the forest.  Also, because they cover ground two to three times faster, they can traverse more terrain per day if they trot along pipelines instead of meandering among the trees.  This is all intuitive and has been suggested before, but now we have a quantification of wolf movements along linear features compared with undisturbed forest habitats.

Implications, and what can be done?

Unless woodland caribou learn to avoid them, linear features are probably increasing their mortality rate because of the advantage provided to wolves.  This still has to be tested, but the results presented by Dickie et al. are consistent with research and observations in other ecosystems where large predators are quick to use human disturbances to increase their hunting success.  For example, African wild dogs chase their prey into fences where they kill them easily, lions use tourist vehicles as cover to reduce their chase distances, and so wolves can also be expected to seize any advantages that humans inadvertently give them.  Meanwhile, new linear features are being created and disused ones remain as scars on the landscape that heal very slowly, especially in boreal ecosystems.  So this study adds an important functional component to the aesthetic argument for requiring industrial developers to make good the damage inflicted by linear features on terrestrial ecosystems.  Replanting indigenous trees is a given, but while the saplings are growing it should be possible to fell some trees, or drag windfallen trees, or erect biodegradable barriers such as sections of picket fence, across disused tracks to make them less useful to wolves.  Priority should be given to remediating long and straight tracks, and approval of new cut-lines should be contingent upon a quantification of similar existing features in the area.  As we now know, they can fall into the wrong hands – or paws.

boreal forest
Aerial view of Canada’s boreal forest, showing linear features on the landscape. Source: Natural Resources Canada (Govt. of Canada) website: http://www.nrcan.gc.ca/forests/boreal/18206

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