Barriers To Long-Distance Mammal Migration
The migratory patterns of ungulates (which are mostly large mammals) are shifting and becoming increasingly constricted in response to a variety of pressures, and the scientific community has been taking notice. With growing awareness about “imperilled migrations” and a new sense of urgency for protecting migratory species, there is also rapid development of new techniques to help identify remaining migratory paths to inform conservation and management decisions. Fortunately, new types of modelling and software have made understanding migratory patterns a more feasible task than it was before.
This is a good thing, because migratory patterns are under threat. Specifically, the continued expansion and new development of oil and gas reserves is “causing conflict between corporations, land managers, and conservationists concerned with retaining intact ecosystems from arctic to desert to marine systems.” Oil and gas development can have a serious negative impact on migratory patterns even when well-managed, but according to this article, “developers are extracting petroleum without understanding the impacts on migratory species.” In a similar manner, highways and other roadways break up wild animal habitats. These two phenomena have a serious combined effect on native animal species.
To better understand how migratory patterns are being impacted, researchers in this study followed pronghorns in Wyoming and used radio collars to understand the movement and obstacles faced by this particular species. The objectives were three-fold: 1) to identify the specific locations of existing threats; 2) to quantify responses to human-caused disturbances; and 3) to identify important areas in need of protection for migrating animals. They found that 71–84% of radio-collared pronghorns migrated each year, and “the average migration length was 52.83 km over 22 days.” Digging into the data further, pronghorns spent 78% of their time in stopovers during the spring migration. In all years observed, the pronghorns tended to avoid areas of gas field development. The researchers also found that “highways appeared to represent obstacles to pronghorn in some locations but be (sic) permeable in others.” Some highways presented more significant obstacles based on traffic levels and fencing type.
The researchers note that, “as development of petroleum resources continues to expand globally, the displacement of migratory wildlife and the threats to long-distance migration increase.” They show that pronghorns did their best to deal with obstacles in their path and adjusted their behaviour in various ways to deal with obstacles of varying severity. Overall, the researchers note that “migrations can be restored if [human-caused] barriers, such as fences, are identified and removed or modified. Where the barrier itself cannot be changed, as in the case of a highway, construction of wildlife over- and underpasses should be considered.”
For wild animal advocates, these types of studies underline the need to find effective ways to protect particular species and that every species has their own unique context. By using modelling that takes into account as many factors as possible, researchers can identify the most important impediments to animal migration. This is information advocates can use to help animals as effectively as possible.