Climate change is helping avian disease advance on some of the world’s most remarkable birds.
By Nathan Collins
(Photo: Wikimedia Commons)
From ocean beach to mountain top, Hawaii was once full of birds, but populations went into decline beginning in the late 19th century. While ornithologists were cautiouslyoptimistic that native birds might be able to recover, a new report suggests some of Hawaii’s most famous native birds may be on the verge of extinction—and a harbinger for worse things to come.
The rare Hawaiian honeycreepers are among the most varied bird families around, a consequence of what’s called adaptive radiation, the same process that produced Darwin’s famously diverse finches. Although they once roamed from coast to coast on the islands, Hawaiian honeycreepers are now largely confined to mountain landscapes, where cold temperatures keep mosquitoes and the diseases they carry—notably, non-native avian malaria and avian poxvirus—at bay.
But as climate change causes temperatures to climb, avian diseases and their mosquito vectors will likely creep up mountainsides as well. Combined with the ongoing threat posed by non-native plants and animals, that could spell serious trouble for honeycreepers, Eben Paxton and his colleagues write this week in Science Advances.
Although they once roamed from coast to coast on the islands, Hawaiian honeycreepers are now largely confined to mountain landscapes.
To get a clearer picture, Paxton and his team looked to bird surveys conducted periodically since 1981 on Kaua’i’s Alaka‘i Plateau, the crater of an extinct volcano and the place where all of the island’s native birds now call home.
Six of the seven native honeycreeper species were in serious decline, the team found. Best off is the Kaua’i ‘Elepaio (Chasiempis sclateri), but even that species is losing about 900 individuals a year. The ‘Akeke’e (Loxops caeruleirostris) is faring much worse. While it numbered more than 15,000 at the turn of the millennium, today there are fewer than 950, and it’s retreated to a smaller core territory at generally higher elevations. Based on past trends alone, the ‘Akeke’e will go extinct around 2028, according to a fairly conservative estimate.
In contrast, a number of non-native species are actually doing pretty well. The Japanese bush warbler (Horornis diphone), for example, has seen more than a three-fold increase in its numbers since 1981.
It’s possible the spread of disease, degradation of habitat, competition with non-native birds, and ongoing pressure from predators have all contributed to the decline in native bird populations in Kaua’i. The fact that many honeycreeper species are moving to smaller areas at higher elevations, however, suggests the birds are in retreat from an advancing army of disease aided by global warming.
“The potential extinction of [honeycreepers] will likely continue to reduce the ecological integrity of the island’s forest and result in continued degradation of ecosystem processes,” the researchers write. “Our findings clearly demonstrate the rapid effects that climate change can have on species with small geographic ranges and specific climatic constraints.”