EVEN when they tiptoe discreetly through the undergrowth, nature lovers and ecotourists may be having an unexpectedly damaging impact on wildlife. A study of protected Californian forest has shown that hiking, wildlife-watching and similar low-impact activities are linked to a sharp drop in numbers of carnivores such as bobcats and coyotes.

"We saw dramatic, fivefold reductions in the native species," says Adina Merenlender of the University of California, Berkeley, who ran the study with Sarah Reed of the San Francisco-based Wilderness Society.

Ecotourism is big business.

In 2004, it grew three times as fast as the tourist industry as a whole. One in five tourists now go on eco-holidays. It has been shown to have an impact on a range of species, from dolphins and dingoes to penguins and polar bears (New Scientist, 6 March 2004, p 6). The dilemma is that revenue from ecotourism provides one of the best incentives for local communities to protect endangered animals instead of hunting them.

Philip Seddon, a wildlife management specialist at the University of Otago in Dunedin, New Zealand, says the finding that such apparently harmless activities may alter the make-up of wildlife communities challenges the main concept of ecotourism - that it minimises impacts and maximises benefits. Reserve managers may in future have to make more areas off-limits to tourists.

Merenlender and Reed focused their study on 14 protected zones of oak woodland in northern California. At each site they collected faeces left by the target species along a series of 500-metre sampling paths. They then compared the quantity found in areas out of bounds to humans with that found along sampling paths in similar "paired" areas nearby where access was allowed.

When people were banned from an area, native species such as bobcats, coyotes and grey foxes thrived and were typically five times as abundant as in more heavily trafficked areas. Likewise, faeces of domestic animals, particularly dogs, were only found in the areas visited by humans.

It is well known that human activity can alarm animals, but Merenlender says this is the first time a consistent effect has been demonstrated across entire communities. "We see it over the whole park, not just a single trail."

This should not, however, be taken to mean that low-key ecotourism is always harmful, says David Sheppard, head of the programme on protected areas run by the International Union for Conservation of Nature (IUCN). "It's hard to make generalisations. It can depend heavily on species, as some are more affected by recreation than others."

Large predators might be unusually sensitive to human activity because people hunt them. "These animals have high intelligence, and those that are cautious survive," says Paul Eagles, who studies ecotourism at the University of Waterloo in Ontario, Canada, and chairs the tourism task force of the IUCN's World Commission on Protected Areas. Even animals that habitually follow trails used by humans are adept at keeping out of sight when people pass.

Merenlender, however, points out that her sampling paths cut across trails and non-trail areas, so the differences couldn't be dismissed as animals temporarily ducking out of sight. "We looked on and off-trail,and found low abundance off-trail too in accessible areas."

The team, who report their findings in Conservation Letters (DOI: 10.1111/j.17550263X.2008.00019.x), suggest several strategies for reconciling the needs of wildlife and people.

One is to ensure that visitors stick to prescribed trails and do not penetrate deep into protected habitat. Others include introducing permit systems and restricting access to certain times of the year.

"We're not in any way advocating that people stop seeing nature," Merenlender says. "But we're trying to heighten the awareness of site managers to these unexpected impacts on wildlife."

Seddon agrees that the study's results deserve to be taken seriously. "We're faced with decisions about how best to manipulate protected areas," he says. "Perhaps we need areas set aside from virtually all human use."

Source: New Scientist