Brown footed boobies stand watch at Johnston Atoll NWR. Photo credit: L. Hayes/USFWS
Johnston Atoll National Wildlife Refuge is 750,000 square miles from anywhere. In the middle of the Pacific Ocean, this collection of four islands – the biggest being 640 acres – provides one of the only rat free, safe nesting places for seabirds and shorebirds in the Pacific Remote Islands.
Greater frigate bird and chick in their nest on Johnston Atoll NWR. Photo credit: Laura Beauregard/USFWS
That is until the yellow crazy ants invaded.
Likely brought to the island by humans, yellow crazy ants (Anoplolepis gracilipes), are highly mobile and can easily become established and dominant in a new habitat. A hardy survivor, the yellow crazy ant is part of a group of ants known as tramp ants. Their range is primarily limited by how far they can travel and hitching a ride with humans takes them to places unprepared for such mighty invaders. Places like Johnston Atoll NWR. The yellow crazy ants quickly took over at the island of Johnston Atoll and wreaked havoc on the thousands of nesting seabirds.
When yellow crazy ants invade, their numbers increase to such a high density they swarm and overrun anything on the ground.
Yellow crazy ant swarm a red-tailed tropic bird. Photo credit: Stefan Kropidlowski/USFWS
Seabirds nest on the ground, leaving them vulnerable to the swarms of yellow-crazy ants. Nesting seabirds and chicks have visibly suffered from attacks by the yellow crazy ants. The yellow crazy ant uses formic acid to incapacitate their prey. Effects from the formic acid and these attacks range from swollen eyes and loss of vision to reproductive failure for one or more years.
A chick before and after being swarmed by yellow crazy ants. Note the damage around the eyes and to the beak. Photo credit: Sheldon Plentovich/USFWS
Invasion by yellow crazy ants eliminates suitable nesting habitat in invaded areas. Since seabirds are highly site faithful, it is likely that they will not pick others areas in which to nest, thus eliminating reproduction for an unknown number of years.
In 2010, the U.S. Fish and Wildlife Service started a project to eradicate yellow crazy ants from Johnston Atoll NWR. Refuge staff, with funding from the Refuges Invasive Species program and partnering with the Pacific Islands Coastal Program, leads the project.
According to Sheldon Plentovich, who is the Pacific Islands Coastal Program Coordinator and studied the effects of ants on seabirds as part of her dissertation, the secret to success is the new ideas and solutions generated through collaboration. The yellow crazy ant eradication project at Johnston Atoll NWR works with experts at universities in the U. S. and Australia, as well as the U.S. Geological Survey, and the U.S. Department of Agriculture
“So far, we’ve been successful at reducing ant densities by more than 90 percent,” said Plentovich.
More than 15 species of birds rely on the refuge for safe nesting sites, including three species of boobies, sooty terns, greyback terns, red-tailed and white-tailed tropic birds, greater frigatebirds and several species of shorebirds.
A healthy red-tailed tropicbird and chick nest peacefully without the threat of yellow crazy ants. Photo credit: Sheldon Plentovich/USFWS
“We are already seeing such improvement. The red-tailed tropic birds are coming back. We can see the effect of all the hard work,” said Pacific Reefs NWR Complex biologist Lee Ann Woodward. “Johnston Atoll NWR is one of the last oases for seabirds and is a crucial part of their survival.”
Seabirds take flight above an old military bunker on Johnston Atoll NWR. Photo credit: Susan White/USFWS