Bears without borders

Wildlife monitoring often happens at the national level: Managers count the number of animals in their country to gauge how well a species is faring. But in a new study, researchers point out a problem with this approach. “While policy makers and wildlife managers have to respect the borders of their jurisdictions,” they write, “wild animals under their auspices do not”. In other words, animals can move from country to country. And when neighboring nations conduct their surveys separately, animals may be double-counted — leading to inflated estimates.

To find out how much these border crossings distorted findings, the team turned to a brown bear monitoring program in Norway. From 2009 to 2013, people gathered hair and feces from the bears. Genetic analysis of 843 samples allowed researchers to identify 105 female bears.

The program obtained most of the samples in eastern Norway, which borders Sweden, Finland, and Russia. Twenty female bears and 54 male bears found by the Norwegian program showed up in Sweden’s surveys as well, “which provides firm evidence of trans-boundary movements,” the authors write. The team estimates that 30 to 49 percent of the females detected by Norway had “centres of activity” in other countries.

The researchers also ran different versions of models to predict population size. A model that did not account for border crossings inflated the estimated number of female brown bears in Norway by 72 to 119 percent, they report. For example, that model estimated that 73 female brown bears lived in Norway in 2013. A model that accounted for border crossings estimated only 35 female bears.

Of course, “visiting” animals improve biodiversity and affect ecosystems wherever they go, regardless of whether that country is their primary residence. But managers in neighboring nations should work together to ensure they aren’t double-counting, especially in smaller countries, the authors argue. Roberta Kwok | 28 May 2015

Source: Bischof, R., H. Broseth, and O. Gimenez. 2015. Wildlife in a politically divided world: insularism inflates estimates of brown bear abundance. Conservation Letters doi: 10.1111/conl.12183.

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