U.S. National Parks Under 'Deep and Immediate Threat' From Feral Cats, Hogs, Rats and Other Invasive Species

National Parks in the United States are "struggling" to deal with the "huge" threat of invasive terrestrial and aquatic species, researchers have warned.

Invasive species have been reported in more than half of National Parks, posing a "deep and immediate threat" to the Park Service's mission to preserve America's most precious natural ecosystems, according to a study published in the journal Biological Invasions.

"Invasive species are non-native species whose introduction does or is likely to cause economic or environmental harm, or harm to human health," lead author of the study Ashley Dayer, from Virginia Tech and the Department of Fish and Wildlife Conservation, told Newsweek. "Our findings focus on invasive animal species including mammals, birds, fish, reptiles, and amphibians."

The National Wildlife Federation describes invasive species in the U.S. as one of the leading threats to native wildlife.

Another author of the study, Mark Schwartz from the University of California, Davis, said invasive species cause demonstrable harm to natural ecosystems by displacing other species, driving extinctions, disrupting food webs, and interfering with several other ecological processes. They often reproduce and spread quickly, increasing their potential to cause environmental damage.

Among the worst offenders in the U.S. are invasive rats, as well as feral cats and hogs.

"Invasive rats, cats, and mosquitos carrying disease (avian malaria) have caused the extinction of endemic island birds in the Pacific, such as Hawaii," Dayer said. "There and throughout much of the U.S., feral hogs destroy wildlife habitat impacting birds and small mammals. Likewise, feral cats are considered to be among the most destructive invasive species globally for their predation of birds and other animals."

Another massively problematic species is the Burmese python which has invaded the Everglades National Park in Florida—leading to an estimated 60 percent reduction in the number of birds and mammals there over the past couple of decades.

Schwartz told Newsweek that invasive species are now a "huge" issue in national parks and that the problem is "far, far worse now" than it was twenty years ago. Invasive species are often spread by human activities. And as the world has become more globalized, the rate of new introductions has increased.

For the study, researchers examined the threat of invasive species in America's national parks—more than half of which are battling an invasive animal issue.

"Invasive animal species are a widespread problem for U.S. National Parks," Dayer said. "According to a data call of park units, there are 331 invasive animal species known to be in parks, with a total of 1,409 populations of those species."

"Most concerning is that only 11 percent of these populations are controlled. These species are negatively impacting native wildlife and plant and tree species in the parks, recreational opportunities, and costing millions of dollars to manage," she said.

The authors urge the NPS to make tackling this issue a priority, while noting that trying to address the threat on a park-by-park basis will not be sufficient. Instead, they recommend a "system-wide" collaborative approach to addressing the problem.

"Despite the magnitude of this problem, NPS lacks a system-wide approach to address the invasive animal species," Dayer said. "The current piecemeal approach needs to be replaced with a more strategic approach, coordinating among parks and with other conservation partners."

The authors also note that public outreach campaigns are an important part of the puzzle. These could help to change behaviors and reduce the spread of invasive species.

Everglades National Park
The sensitive ecological landscape of the Everglades National Park, home to many endangered and rare plants, is seen from the air on March 16, 2015 in Miami, Florida. Joe Raedle/Getty Images

"It is essential for the parks to engage with the pubic on this issue. NPS has a well-respected outreach and interpretation program that could be harnessed further to work with the public on understanding the implications of invasive animals in parks and what they can do," Dayer said.

Preventing invasive species from entering parks in the first place is a key factor. And this involves collaboration with the public.

"Prevention of spread is the most important thing we can do. Members of the U.S. public can play an important role in addressing this challenge," Dayer said. "First, people can take care to avoid spreading invasive species such as aquatic pests that hitchhike on boats or pets that can cause impacts if released."

"For example, when moving boats between water bodies, boaters are encouraged to clean, drain, and dry them. The public can also get involved in activities to detect, monitor, and remove invasive species," she said. "They can also get involved in voicing their thoughts about these issues."

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