Formed entirely by volcanic action about 4,000 km (2,400 miles) from the nearest continental land mass, Hawai`i is the most isolated group of islands in the Pacific. Except for the Hawaiian bat, no terrestrial mammal naturally colonized the islands. Isolated from the enemies of their ancestors, Hawai`i’s native plants and animals gradually lost their natural defenses against mammalian predators.
With human settlement in Hawai`i many predator mammal species were introduced; mice and rats (carried on early sailing ships), cats (soon after Captain Cook), and the mongoose (intentionally introduced in 1883 to control rats).
Predation by rats, cats, and mongooses is considered a leading cause in the decline and extirpation of endemic Hawaiian birds. Habitat destruction and avian diseases are other important causes. Many extinct Hawaiian birds, known only from fossil remains, nested on the ground and were susceptible to predation.
Only two methods for controlling small mammals are available to land managers – trapping and 0.005% diphacinone bait placed in bait stations. Both methods, effective in small areas, are labor- and time-intensive and are impractical for large conservation areas. Scientists from Federal, State, and private organizations in Hawai`i are currently studying the ecology and biology of small mammal predators, and evaluating new control techniques, to develop management tools to lessen the impacts of these predators on native wildlife and plants.
One new tactic to protect ground nesting birds has been ‘predator-proof fencing’. Success of the first predator proof fence in the United States is producing dramatic results that may eventually lead to a resurgence in decimated seabird populations in Hawaii. The Wedge-tailed Shearwater, which nests in the remote coastal dunes on the now-fenced Kaʻena Point at the northwestern tip of O’ahu, has produced the highest number of chicks since the annual survey began in 1994.
“This is extraordinary news. It has been only eight months since the predator-proof fence was installed and already, we are seeing results. This year’s chick count of 1775 is a 14% percent increase over the previous high count in 2007 and the highest number ever recorded at the point. So far, the fence has done a great job of preventing bird predation by rats, cats, mongoose, dogs, and even mice,” said Dr. George Wallace, Vice President for Oceans and Islands at American Bird Conservancy (ABC), the leading bird conservation group in the United States.
The project has been a cooperative effort involving Hawai’i’s Department of Land and Natural Resources (DLNR), the U.S. Fish and Wildlife Service, the Hawaii chapter of The Wildlife Society, and local communities.
Ground-nesting seabirds in the area, which also include the Laysan Albatross, have been targets of predation by introduced mammals, with the result that up to 15% of chicks are killed each year. The predators have especially preyed on the young birds before they can fly, but they also eat seabird eggs and even attack adult birds.
The marine grade, 2,040-foot long, 6.5-foot-high, stainless steel fence was installed to create a 59-acre area enclosure at Ka’ena Point Natural Area Reserve. The fence is the first of its kind in the United States, having been used successfully in 30 New Zealand coastal and forest projects, and tested on lava flows on the Big Island. The fence provides a combination of features including a rolled hood at the top, fine mesh between the fence posts, and a skirt buried underground, designed to prevent animals from jumping or climbing over, squeezing through, or digging their way under the fence and into the protected area.
In addition to the shearwaters, native plants such as the endangered ’ohai and other coastal strand vegetation are benefiting from removal of rats and mice which eat flowers, seed pods, and seedlings. Native species are being monitored to document the effects that the removal of predators will have.
While I knew that any mammal could wreak havoc on our native flora and fauna it wasn’t until I visited Bowman’s Hill Wildflower Preserve in Buck’s County, PA that I realized the extent of damage an abundance of a certain species. I drove to the front gate at Bowman’s Hill Preserve and was surprised to see a towering chain-linked fence and and automatic gate. I knew the fence was designed and installed to keep out the plethora of deer, still I was surprised to see the extent they went to keep them out at all costs.
It was only seconds after passing through the automatic gate that I found myself hitting the car brakes and gasping in awe. It was at that moment that I realized that I have never seen what this country ‘could’ look like if we didn’t have an over population of any one species or any invasive alien species–all I can say it was absolutely mind-bowing!
Shortly afterwards a tear ran down my cheek as I stared into what was a true deciduous Pennsylvania forest not browsed by deer and not a single invasive alien plant to be seen… at that moment I could only imagine what this county would look like if humans were far more conscious of bringing here and if we didn’t remove so many of the predators that rely on deer for their food. What we are missing out on when we go into less populated areas is enormous and I’m fearful that most of us will never know what could be outside our own doors.
While I don’t necessarily enjoy seeing towering fences, or other types of fences to keep predators out to protect our native species (flora and fauna) I am in support of doing things that help preserve what we do have left; those natural things that once graced this land long before we upset the apple cart.
Source: American Bird Conservancy