Data from helicopter surveys of the invasive Himalayan tahr that has spread through New Zealand’s Southern Alps is helping the country’s conservation agencies better manage ungulates.
Himalayan tahr (Hemitragus jemlahicuslisten)) are a type of furry goat native to the mountains of its namesake, primarily in parts of northern India and Nepal. These ungulates have been introduced to several countries around the world like Argentina and New Zealand to provide hunting opportunities. In New Zealand, which has no native mammals other than bats and marine mammals, the tahr was introduced in the early 20e century. While hunters may have relished the opportunity provided by the goats, the tahr damages native plant species, especially tussock grasses in the high elevations where the tahr thrives.
“If populations get too high, they can cause damage to the natural environment, overgrazing tufted alpine grasslands,” said David Ramsey, wildlife manager at the Victoria Department of Environment, Land, Water and Planning, a Australian state agency.
No predators other than human hunters control the number of tahrs in New Zealand. The government has an obligation to maintain the number of tahr at 10,000 animals. But no one had made a solid effort using modern techniques to estimate the true numbers of species across their entire range.
Over the summers and autumns of 2016 to 2019, wildlife managers helicoptered over 117 patches of the Southern Alps that were all two square kilometers in size. They flew over each of these plots recording every tahr they spotted. They returned to survey the same plots twice more over the next two months.
Ramsey has often worked in New Zealand over the years, so wildlife managers contacted him to process and analyze the data to estimate how many tahr actually roamed the Southern Alps.
Ramsey chose to build a model to estimate the global tahr number in a study recently published in the Wildlife Management Journal. In doing so, he and his colleagues added evidence that explained the fact that the local population in the plots likely changed quite a bit in the weeks between each survey as the animals moved in and out of the areas.
With these factors, the researchers estimated population numbers for the entire area, which includes seven tahr management units and two exclusion zones.
They found that there were around 34,500 tahr on public conservation land in the Southern Alps, not including ungulates that likely lived on privately managed land in the area. This is more than triple what the management plan anticipated.
Surveys also revealed that tahr density is high in some areas, with up to 33 animals per square kilometer. While they were still in other areas such as glaciers or snowfields, they were often less densely populated there.
“There was quite a wide range of tahr densities in this landscape,” Ramsey said.
The government has already begun to act on the results of these investigations, although some of these actions are controversial, with hunters on the one hand valuing the tahr as a cultural and recreational resource, and conservationists, who are more concerned about their impact on native ecosystems. . Agency personnel have shot down a few tahr from helicopters, particularly in high-density and environmentally sensitive areas where they are likely to cause the most damage.
They also tried to encourage increased harvesting by recreational hunters. But hunting these species is difficult, as you often have to climb a lot of rough terrain just to get to them.
Ramsey said these surveys, since they are the first, can provide a basic idea of the number of tahr in the region. Future surveys can use this as a point of comparison to determine if the population is changing over time or if management measures are having an impact.
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