Invasive Species, Rising Seas Threaten Seabirds

posted in: September 2012 | 0

At this year’s Hawai`i Conservation Conference, held once again at the Hawai`i Convention Center in Honolulu, scientists and natural resource managers recounted their successes in improving native ecosystems and protecting native species. They also expanded on their assessment of the potential effects climate change may have on Hawai`i’s terrestrial and marine environments.

This year’s theme was, “What Difference Does 20 Years Make? Reflections on Change, Innovation, and the Work that Remains.” The following provides a glimpse of some of the successes that have been achieved as well as the work to be done with regard to seabirds in the Northwestern Hawaiian islands and other remote atolls, which are threatened both by climate change and invasive species.


Strike Team Vanquishes

Crazy Ants at Johnston

“Cool. Ants usually seem so freaking indestructible,” one audience member told another after Stefan Kropidlowski finished his talk at the conference.

Last year, armed with squirt guns filled with a mixture of canned cat food, Karo syrup, and pesticide, a trio of young men all but rid Johnston Island of yellow crazy ants, saving birds there from having their eyes swollen shut by stings and their feet webbing laced with sores. In short, the men gave the birds their home back.

Kropidlowski, a University of Hawai`i-Hilo student and U.S. Fish and Wildlife Service (FWS) crazy ant strike team leader, presented the results of his efforts to control the ants, which had formed a super-colony spanning nearly a quarter of the remote island. Johnston Island is one of four small islands that make up the Johnston Atoll National Wildlife Refuge, which is located some 750 nautical miles southwest of Honolulu.

Johnston is “the only available seabird nesting habitat in over 750,000 square miles of ocean and hosts 15 breeding species, including what may be the world’s largest population of red-tailed tropicbirds (Phaethon rubricauda),” Kropidlowski write in the abstract of his talk.

In January 2010, an infestation of yellow crazy ants (Anoplolepis gracilipes) was discovered throughout 54.7 hectares of the 241-hectare island.

Yellow crazy ants, one of about 50 ant species introduced to Hawai`i, subdue their prey with formic acid, which can irritate the eyes and feet of birds, according to Sheldon Plentovich of the FWS. During her talk, which preceded Kropidlowski’s, Plentovich showed video from Johnston Island of a tern frantically tapping its feet on a branch to shake off the ants and a red-tailed tropicbird sitting in an infested area that “looked like a zombie bird.”

Kropidlowski said he saw birds, blinded by ant bites, hit trees on takeoff. Most ground-nesting seabirds within the infested area fled.

By August, the FWS’s strike team was on the ground. They first attempted to treat infested areas with a pesticide that had successfully controlled yellow crazy ants found on Mokapu, O`ahu. It didn’t work and the infestation spread.

During one survey, the team found 800 to 1,000 queens in one 4-by-6 meter plot.

After more than a year of unsuccessful control treatments, the team switched pesticides last November and started using baits of cat food (for the queens) and Karo syrup (for the workers), delivered about a liter at a time via squirt gun. The team spent 24 days spread out over 13 weeks treating a total of 52.16 hectares.

By mid-June, it had reduced the ant population to below detectable levels. The birds responded almost immediately. Before treatment, fewer than 24 red-tailed tropicbird nests remained in the infested area. In the weeks following the ant population decline, the number of nests grew to 524. At last count, 5,212 breeding pairs inhabited the island, which accounts for 32 percent of the global population estimate, Kropidlowski said.


Scientist Refine Assessment

Of Effects on Birds

Of Sea Level Rise

At last year’s Hawai`i Conservation Conference, one poster suggested that a few low-lying islands at French Frigate Shoals (FFS) in the Northwestern Hawaiian Islands would all but disappear with a two-meter rise in sea level. Another poster discussed how inundation zones can increase exponentially if wave action is included in combination with sea-level rise scenarios.

This year, presentations on the possible impacts of climate change on seabird nesting habitat in the NWHI continued. Since last year, researchers using GIS models have revised their estimates of impacts to FFS and now believe four low-lying islands there will be completely submerged if sea level rises two meters by 2100.

For Midway Atoll, scientists with the U.S. Geological Survey, the University of Hawai`i, and the U.S. Fish and Wildlife Service attempted to assess which bird species are most vulnerable to sea-level rise. In their modeling, the results of which were presented in a poster, Karen Courtot, Michelle Reynolds, and Crystal Krause of the USGS, the university’s Paul Berkowitz, and Elizabeth Flint of the FWS, chose not to incorporate wave action into their models, but did consider possible effects of groundwater rise.

To assess the vulnerability of each species, the researchers considered whether the birds breed during storm seasons, how well they can adapt to changes, and their population status. Of the 20 or so bird species that nest at Midway’s Sand, Spit, and Eastern islands, they found that black-footed albatross were the most vulnerable, followed by Laysan albatross, Tristram’s petrel, Bonin petrel, and grey-footed terns. Terns and boobies were found to be the least vulnerable to sea-level rise.

“Unique among terns, gray-backed ranked amongst the most vulnerable species,” they wrote.

Sand, Spit, and Eastern islands total 604.2 hectares. Modeling indicated that a rise in sea level of two feet would reduce the total nesting area of those islands by 12.5 to 18.9 percent, depending on whether a concurrent rise in groundwater levels was considered. Species nesting in southeastern Sand Island and the western end of Eastern Island are the most vulnerable to inundation, they found.

Based on a two-meter sea-level rise scenario and 2011-2012 nesting abundance data, Laysan albatross stood to lose 28,445 nests without a rise in groundwater levels. Using 2008 breeding season data, they found that Bonin petrels stood to lose more than 7,000 nests. If groundwater rises, nest loss is expected to be more than double those numbers for both species, their poster stated.

“Limited resources to monitor climate change impacts to seabirds at the nesting colony could be best allocated to the most vulnerable species,” they wrote.

They noted that models that don’t consider wave run-up underestimate inundation during storm events.

“Wave-driven inundation models will further improve our understanding of the areas most vulnerable to climate change impacts,” they wrote.

–Teresa Dawson

Volume 23, Number 3 September 2012