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Drier climate seen as threat to isle forest birds

Michael Tsai
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U.S. FOREST SERVICE

Life-cycle changes, such as breeding and molting, were found to shift in native Hawaiian birds, such as the iiwi, coinciding with climate-related changes to native vegetation.

A new study by U.S. Forest Service researchers suggests that the impact of climate-related changes on native Hawaiian birds may be even more substantial than previously understood.

Scientists from the service’s Pacific Southwest Research Station took a fresh look at climate, vegetation and bird data collected at a 40-acre monitoring site on Hawaii island between 1976 and 1982. Their findings, published in the November edition of the science journal Ecology, found that the breeding seasons for three native birds — iiwi, apapane and Hawaii amakihi — were timed with the availability of ohia lehua flowers, which was in turn dependent on periods of heavier rains.

Similar relationships were found in certain native and non-native bird species in relation to food sources and the timing of molting, the period when birds replace their feathers. These close connections supported the conclusion that climate conditions affect the availability of food sources, which then affects the abundance or scarcity of certain birds.

This enhanced understanding does not necessarily bode well for Hawaii’s birds.

“The susceptibility of many Hawaiian birds to climatically induced changes in their food web is alarming when considering that the archipelago has been subject to an increasingly drier climate during the last 30 years,” said lead author Jared Wolfe, a research eco­logist.

Once again, Hawaii’s relative geographic isolation proved a valuable factor in the research, allowing the scientists to study the interaction between native birds and plants without other factors that could potentially mask climate effects.

“These types of studies are rare because they tend to depend on long-term data and labor-intensive field work,” said C. John Ralph, an emeritus research ornithologist who participated in the study. “But findings from long-term studies, such as this one, are critically important because they provide insights into how changes in climate might affect organisms in seemingly indirect ways.”

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