The populations of six forest bird species on the Hawaiian island of Kauai are collapsing, according to a new study published September 7 in the journal Science Advances.
The one-two punch of avian malaria and climate change that we wrote about in December 2015 are driving the declines, say lead author Eben Paxton, of the U.S. Geological Survey Pacific Island Ecosystems Research Center, and his colleagues. And the ongoing incursion of non-native plants and animals is also a factor.
The findings differ from an earlier, more “cautiously optimistic” assessment of Kauai native birds based on survey data from 1981 to 2000. Paxton and his team included data from 2000 to 2012 in their analysis of native bird species on the island, providing clearer insights into how the abundance and distribution of native birds on Kauai has changed in recent decades.
Out of the seven native forest bird species they studied, six species (all Hawaiian honeycreepers) showed population declines in both their periphery and core ranges by averages of roughly 94 and 68 percent.
“If native species linearly decline at a rate similar to or greater than that of the past decade,” they write, “then multiple extinctions are likely in the next decade.”
Here’s what they found about each species.
‘Akikiki. This small gray and white honeycreeper, listed as federally endangered in 2010, is endemic to Kauai. It declined 71 percent from 1981 to 2012 and 7 percent from 2000 to 2012. The authors estimate its population in 2012 was 468 individuals.
‘Akeke‘e. This yellow and olive honeycreeper, also listed as federally endangered in 2010, is found only in the mountains of Kauai. Its population declined 48 percent from 1981 to 2012, but in the last 12 years of the survey period, it went into a free-fall, dropping by 98 percent, to an estimate of 945 birds.
‘I‘Iwi. A red bird with black wings and a curved pink bill, it is common on Maui and the Big Island and uncommon or rare on Oahu, Lanai and Molokai. On Kauai, its interior population dropped 86 percent, while the exterior group fell 97 percent. The researchers estimate a 2012 population on Kauai of 2,603 birds.
‘Anianiau. Weighing only 9-10 grams, this is the smallest Hawaiian honeycreeper that still exists. From 2000 to 2012, the mostly yellow bird lost 57 percent of its numbers in the core area of its range and 91 percent on the exterior. The Kauai endemic’s 2012 population estimate was 10,787 individuals.
Kauai ‘Amakihi. This olive green endemic lost 91 percent of its core and 98 percent of its exterior populations from 2000 to 2012. Researchers say it had a population of 6,519 birds in 2012.
‘Apapane. This red beauty, found throughout the major Hawaiian islands, had a large, robust population at the beginning of the survey period. Nevertheless, its core population on Kauai declined 67 percent, and the exterior group fell 89 percent, leaving about 98,506 birds in 2012.
Kaua‘i ‘Elepaio. This small, gray-brown monarch flycatcher is the one bird species surveyed that doesn’t seem to be affected as much by disease, possibly because it comes from a lineage that colonized Hawaii more recently than Hawaiian honeycreepers. Its periphery group fell by 64 percent, but its core population increased by 88 percent, to an estimate of 82,437 birds in 2012.
Puaiohi. This secretive thrush, which has been listed as federally endangered since 1967, lives in narrow river gorges only on Kauai and was not part of the survey. However, the authors note that it “may be more tolerant of avian malaria, and although population trends are uncertain, there is no evidence of rapid declines based on the monitoring of several breeding populations for the species.” In 2010, its population was believed to be about 500 birds.
The relatively sudden change in the honeycreepers’ status since 2000 “suggests that a threshold has been crossed,” Paxton and his co-authors write. They say the results from Kauai represent an early warning for forest bird communities on other islands such as Maui and Hawaii, as well as for other species around the world that are trapped within a climatic space that is rapidly disappearing.
Read the abstract
Eben H. Paxton, Richard J. Camp, P. Marcos Gorresen, Lisa H. Crampton, David L. Leonard Jr., Eric A. VanderWerf. Collapsing avian community on a Hawaiian island. Published 7 September 2016, Science Advances, 2, e1600029 (2016). Abstract.
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