On the remote island of Nihoa, the invasive gray bird grasshopper appears to be a boom and bust insect, and a severe threat to both native birds and native plants.
(Photo: The east side of Nihoa island viewed from at sea. NOAA Ocean Explorer photo.)
The grasshopper is related to the desert locust, Schistocerca gregaria, which was responsible for the Biblical plauges. Cousin Schistocerca nitens has similar impacts. When its numbers explode, it eats everything in sight—robbing plants of their vitality, and potentially robbing some of Nihoa's 27 species of land and sea birds of both food and shelter.
Even the stiff leaves of the hardy Nihoa fan palm, Pritchardia remota, are chewed dramatically.
“Perhaps the greatest current threat to the native biota of Nihoa is predation by the nonnative grasshopper Schistocerca nitens, which has caused widespread defoliation of the island's vegetation over the last few years,” says the U.S. Fish and Wildlife Service's five-year review of the status of an endangered Nihoa plant, Amaranthus brownii.
The agency reported that in 2006, the native amaranth could not be found at all, although biologists believe it still exists.
While many native bird species are negatively affected, one actually appears to benefit from the grasshoppers. The Nihoa millerbird, one of two native land birds (with the Nihoa finch) feeds on the insects.
The grasshoppers became established first in the main Hawaiian Islands, perhaps in the early 1960s. They were first documented on Nihoa in the early 1980s. The species has subsequently been implicated in the serial defoliation of much of the island's greenery, and researchers are studying ways to monitor and possibly control the insect.
In a paper to be published in the Journal of Insect Conservation, University of Wyoming grasshopper entomologist Alexandre Latchininsky reports the gray bird grasshopper is a threat to some of Nihoa's 26 vascular plant species, 27 bird species and 243 known species of arthropods.
During a drought in 2002-2004, the grasshopper severely denuded the island of plant greenery. Scientists visiting Nihoa said it appeared brown and dead. Then the numbers of grasshoppers crashed as well, perhaps for lack of moisture in the soil, which is required for grasshopper embryonic development, Latchininsky said.
Much of the island's vegetation recovered with subsequent rain, but researchers lack a clear picture of the long term impacts of the grasshoppers.
One of the issues for research and conservation is that Nihoa is so remote and difficult of access. The 170-acre or 156-acre island (depending on which source you believe) lies about 150 miles to the west-northwest of Kaua'i. Its topography is dominated by steep cliffs on the north, east and west sides, and the rocky southern coast can only be used for access during calm weather. As a result, most research trips take place in calm summer weather, meaning science has little good information on what conditions are like during winters, when conditions are generally wetter.
Nihoa is the easternmost island of the Papahānaumokuākea Marine National Monument.
For some great Nihoa photography, see Berkeley professor Peter Oboyski's site from his 2005 visit, http://nature.berkeley.edu/~poboyski/hawaii/nihoa.htm.
A report on University of Wyoming researchers' work on the grasshopper is here: http://www.uwyo.edu/AgCollege/AGNEWS/spring06.pdf.
See a Google Maps aerial view at http://maps.google.com/maps?hl=en&ie=UTF8&ll=23.060484,-161.921289&spn=0.019585,0.040169&t=h&z=15%3E.
© 2008 Jan W. TenBruggencate
