Introduced Japanese White-eye Threatens Native Hawaiian Birds

Feb 20, 2012
Dawn M. Smith

The Apapane, a Honeycreeper, Out-competed by White-eye - Footwarrior

Japanese White-eye have increased their range into the higher elevations of Hakalau Forest NWR in Hawaii and are out-competing more specialized local birds.

A tiny bird, introduced to Hawaii as part of an agricultural pest control project, is now putting native Hawaiian birds at risk. The Japanese White-eye (Zosterops japonicas), which can survive in a variety of habitats, is out-competing local species for food.

Native birds in the upper ranges of Hakalau Forest National Wildlife Refuge, near Hilo on the Big Island of Hawaii, are showing stunted growth, lower juvenile survival rates, and delayed or asymmetric molts which can be attributed to poor nutrition.

Eight Native Hawaiian Birds Affected by White-eyes

The recently published study looked at six species of Honeycreeper, three of which are endangered, plus one Thrush and one Flycatcher species, both of which are listed as Vulnerable to Extinction. Insects provide an important source of dietary protein for all of these species. Most of the birds also consume fruit and/or nectar from the ohia-lehua (Metrosideros polymorpha), one of the most common canopy trees in the forest areas surveyed.

Introduced to Help, the White-eye is now a Threat

The Japanese White-eye was originally introduced into the lower elevations of Hawaii in 1929 as part of an attempt to control insects in agricultural areas. Since the mid-1980s, however, they have been expanding their range, moving into the higher elevations.

And, while the White-eye regularly expand their territories and adapt to a variety of habitats and food sources, the native birds found in these highland areas are specialist feeders, requiring a much more specific habitat and food sources.

Food Restrictions Lower Survival Rates for Native Birds

Prior to 2000, molting for the affected species was recorded between June and October. Between 2001 and 2006, the researchers found various changes in molting patterns and feather condition for all 8 species. These changes included delayed molting, resulting in birds completing their molt during the coldest months of the year at a high energy cost and asymmetric molting, which can affect the birds’ ability to move around. The native Hawaiian birds also had stress bars on the feathers, a sign of poor nutrition.

Juvenile Hawaiian birds also exhibited stunted growth and smaller bills. Smaller bill length affects the ability to feed and results in lower survival rates. In areas where the White-eye is not present in large numbers the native birds do not show these changes.

These findings make a strong case for competition from the non-native birds as a primary factor in the decline of the local species. Efforts must now be directed at reducing the impact of the White-eye on these endangered, endemic birds of Hawaii