FROM Mr. Lapenas' 6th grade class:
Q: Why would there be such an overpopulation of "alien' insect species? One hypothesis the
students came up with was that the birds might find the alien insects
"unfamiliar" as a food source and wouldn't care to try the new cuisine.
The other question we have is: Will the large population of alien insects
species have a negative impact on the native bird population? If so,
why?
A: Dear Mr.
Lapenas' class,
Those are very insightful questions. Nihoa is unusual among the islands of
the Northwestern Hawaiian archipelago in that it does have insect-eating birds living there. Most of the other islands do not. We don't have
detailed diet information for the Nihoa Millerbird or the Nihoa Finch and they may not recognize the new species as food.
They do seem to be very curious and try new things when you watch
them however so it is likely that they would happily eat some of the alien insects as well as their standard
diet. The problem comes with what the introduced insects do to the habitat
and the other native insects. Because they may not have arrived with some
of their own parasites and diseases to keep their populations in check they
have the potential to damage the native vegetation on Nihoa such as the 'ilima and the
ohai. The Millerbirds build their nests in these shrubs so rely on the cover and protection they provide.
All of the methods of introduction of those non-native insects that you
mentioned are possible but you should add one more to the list and that is
that human visitors have accidentally brought harmful insects each time they visited in the past. The refuge now has a strict policy about having
all new clothes and gear that we freeze prior to allowing it on the island
but in prior years things like cockroaches and ants probably hitched a ride
in the food and equipment of visitors to the island.
Most of the birds on Nihoa are seabirds and prefer fish and squid to eating
insects. The insects that do make it out to Nihoa from areas with more insectivorous birds probably have defense
mechanisms that protect them such as bad taste or stinging capability so they may be less tasty to the Finch
and the Millerbird on Nihoa.
The solution to the problem isn't clear yet. We are experimenting at
Midway with chemicals that will kill ants but not hurt native species. There may be parasites or predators that are specific to the harmful
species that we can introduce. Its an area that has room for any ideas that people can contribute.
Thanks for thinking about these problems and coming with such excellent
hypotheses.
Aloha,
Beth Flint
Beth Flint
Click for full size
Beth Flint (above) is a wildlife is a wildlife biologist with the U.S. Fish and Wildlife Service.
The picture above was taken on Necker Island September 22nd and e-mailed back via satellite phone. The birds that Beth is observing are Bulwer's Petrels.
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