BACK in 2002, a group of researchers in the Northern Territory suggested that baiting of wild dogs interfered with pack structures in ways that could lead to more livestock killings than if the dogs hadn’t been baited at all.
Now a study of wolves in the United States has come to a similar conclusion.
A Washington State University study found that as wolf control measures increased, the odds of attacks on livestock increased four per cent for sheep and 5–6pc for cattle - up until wolf deaths exceeded the wolf population growth rate of 25pc.
But it’s not that more wolves mean fewer attacks.
“Consistent with expectations,” wrote researchers Robert Wielgus and Kaylie Peebles, “each additional breeding pair on the landscape increased the expected mean number of cattle depredated by 8 to 9 per cent and each additional wolf on the landscape increased the expected mean number of sheep depredated by 6 per cent.”
The issue with control seems to lie in its effect on wolf pack structures. Packs don’t form randomly, they are a conservative evolutionary response for survival.
When pack structures are disrupted by deaths, the instability can result in more breeding pairs of wolves because old dominance hierarchies break down.
“Furthermore, loss of a breeder in a pack during or near breeding season can result in dissolution of territorial social groups, smaller pack sizes and compensatory density dependent effects – such as increased per-capita reproduction,” the researchers wrote.
“Culling of wolves may also cause frequent breeder turnover and related social disruption – which can result in reduced effective prey use (through loss of knowledge of prey sources and ability to subdue prey) which may also result in increased livestock depredations.”
They concluded that, “although lethal control is sometimes a necessary management tool in the near-term, we suggest that managers also consider testing non-lethal methods of wolf control because these methods might not be associated with increased depredations in the long-term”.
The impact of wild dog control on cattle, native and introduced herbivores and introduced predators in central Australia: Eldridge, S.R., Shakeshaft, B.J. & Nano, T.J. (2002). Read the article online.
Effects of Wolf Mortality on Livestock Depredations: Robert B. Wielgus, Kaylie A. Peebles. (2014). Read the article online.