Will Guam kingfisher survive the Palmyra Atoll experiment?
By Mar-Vic Cagurangan
As long as the brown tree snakes’ unyielding presence on Guam remains uncontrolled, the Guam kingfisher, locally known as “sihek,” will never find its way back to its home island.
“We currently lack tools to eradicate brown tree snakes from Guam, and the continued presence of brown tree snakes throughout the landscape prevents the successful reestablishment of sihek on Guam in the foreseeable future,” according to the U.S. Fish and Wildlife Service.
Hence the agency’s decision to designate Palmyra Atoll as a tentative location for the release of the bird's experimental population. The federal agency is scheduled to release a small number of Guam kingfisher in 2023.
Native to Guam, the sihek was extirpated from the island after the introduction of the brown tree snake and deforestation. The Guam kingfisher was rescued from total disappearance when biologists brought the remaining 29 birds into captivity. Today, 152 sihek live in 25 facilities around the world.
“We plan to remove up to nine in the first year, and fewer than nine in subsequent years to ultimately achieve a target of 10 breeding pairs,” FWS said.
Biologists Ethan Sapp and Cullen Wake expressed support for the FWS’s plan to release the Guam kingfisher into the wild, noting that “a stochastic event, such as disease, could be lethal to the small-sized, captive population.”
They also projected that the number of Guam kingfisher will drop to 25 by 2040 “if breeding is continued while the birds are in captivity.”
“Remaining captive would lead to the loss of genetic diversity and encourage inbreeding,” Sapp and Wake wrote to NFW, commenting on the agency’s proposed plan.
“Not only will they lose genetic diversity, but it will also put them at risk for genetic adaptations that will occur while captive. This in turn will result in a loss of ability for the species to survive under wild conditions,” they added.
But the Guam kingfisher’s survival depends on a successful reintroduction to the wild.
While Guam has been ruled out as a release site, scientists weighed the suitability of Palmyra Atoll for the experimental sihek population. Located north of Kiribati, 5,800 km from its native home, Palmyra Atoll is currently owned and managed by the FWS, The Nature Conservancy and the Cooper family.
“We find that the continued presence of the brown tree snake on Guam means that the sihek's native habitat has been unsuitably and irreversibly altered or destroyed for the foreseeable future such that the proposed introduction of the sihek to Palmyra Atoll outside of its probable historical range is warranted and consistent with our regulations,” FWS said.
Sterling Brumbaugh and Jacob Owens of the Abraham Baldwin Agricultural College Wildlife Society advised FWS against the release of the Guam kingfisher as an experimental population “due to the likely death and lack of reproductive success of the released population.”
They noted that the proposed site for the reintroduction of the Guam kingfisher is not within the native range in which it naturally occurs.
Brumbaugh and Owens cited other ecological factors such as the presence of black drongos in Palmyra Atoll.
“Black drongos have been shown to show aggressive behavior toward other large-size carnivorous birds such as the Javan hawk-eagle, so it is plausible that the Guam kingfisher would receive the same kind of harassment,” they said.
Brumbaugh and Owens also cited the presence of pollutants in the atoll.
“An example of anthropogenic pollution is left over as a residual effect of rat eradication and the possible effects may lead to biological magnification within species on Palmyra Atoll,” they said, “With the effects of residual rat poison, Palmyra Atoll would not be an ideal choice to host an experimental population.”
FWS, however, said the introduction of sihek to Palmyra Atoll is not intended to be a permanent introduction that would support a self-sustaining population.
“Depending on the circumstances, the Service may either terminate the release program, or temporarily pause the release program to address identified issues before resuming,” the agency, adding that its plan includes an exit strategy.
FWS said it would halt the bird’s release if “monitoring indicates the benefits from the Palmyra population no longer outweigh the risks to the species” and it “shows unacceptable impacts on the ecosystem that can be clearly causally linked to the introduction of sihek.”
So far, FWS said preliminary findings indicated that releasing sihek onto Palmyra Atoll “with the regulatory provisions” will “further the conservation of the species.”
“The potential loss of the experimental population would not appreciably reduce the likelihood of the survival of the species in the wild because there are currently no sihek remaining in the wild,” the agency said.