Hilo, Hawaii— The U.S. Fish and Wildlife Service and the U.S Geological Survey have recently analyzed three decades of forest bird surveys conducted at the Hakalau Forest unit of the Big Island National Wildlife Refuge Complex. Analysis of the species over time revealed that management actions have been key to historically positive trends. However, recent trend data suggests that stressors are starting negatively influencing forest bird populations. 

The U.S. Fish and Wildlife Service, through active management of the Big Island National Wildlife Refuge Complex, protects Hawaiʻi’s unique island ecosystems by reducing the impact of invasive species. The refuge serves as an important area of essential habitat for threatened and endangered forest birds in Hawaiʻi. Management strategies vary based on elevation, invasive species, and historic land use. Accordingly, over the past 35 years, the refuge has been managed to specifically protect and conserve endangered Hawaiian forest birds using proven reforestation and invasive species control techniques.  

In the study, scientists analyzed three areas of the Hakalau Forest unit over time, accounting for differences in land use. These areas include open-forest, which was once intensively grazed but the forest canopy remained intact (spanning from low to high elevation); closed-forest, which is relatively unmodified by grazing (low elevation); and re-established forest (high elevation), which was logged and grazed for decades prior, but has since been substantially reforested. By 2019, the re-established forest areas included planted stands of native koa trees up to 30 years old, with some native trees and shrubs in the understory.   

This study compared native forest bird surveys between 1987 and 2019, with a closer look at the population trends in the most recent decade, between 2010 and 2019. Between 1987 and 2010, the surveys generally show an upward population trend; however, for surveys between 2010 and 2019, the trend reversed for most species, and populations are now declining. In the low elevation, closed-forest areas, the number of declining species has doubled and even in the higher elevations of the reestablished forest area, populations have declined.  Birds experiencing downward trends include: Hawai‘i ‘elepaio, Hawai‘i ‘amakihi , ‘akiapōlā‘au, ‘alawī, Hawai‘i ‘ākepa,  ‘i‘iwi, and ‘apapane. The ‘alawī had the most substantial decline. Only the ‘ōma‘o showed an upward trend.   

“This detailed look at the latest decade of Native Hawaiian bird surveys at the refuge offers a reminder of the importance of continuous monitoring and timely analysis in collaboration with management. Forest bird surveys provide scientists and managers information about current population densities, abundances, and trends. This allows managers to evaluate and adapt management actions to enhance forest bird conservation efforts at the refuge complex,” said research scientist Rick Camp of USGS. “Understanding the nuances in the last decade could help us to know how to help these species for many more decades to come.”   

“These downward population trends at lower elevations of the Hakalau Forest unit are highly concerning”, said FWS Deputy Refuge Manager Donna Ball “They demonstrate the continued need for management of the Big Island National Wildlife Refuge Complex, with the support of the community and our partners. This will ensure the refuge serves as a haven for forest birds amidst the many challenges they face.” 

The recent analysis of forest bird populations has been driven discussions about the environmental stressors affecting these species. A collective determination among conservationists, scientists, and local community members about how to best safeguard these ‘feathered forest gems,’ may forge a sustainable path for their melodies to continue filling and resonating within Hawai‘i's forests, for generations to come. 

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The U.S. Fish and Wildlife Service works with others to conserve, protect, and enhance fish, wildlife, plants, and their habitats for the continuing benefit of the American people. For more information, visit www.fws.gov/pacificislands, or connect with us through any of these social media channels at https://www.facebook.com/PacificIslandsFWS, www.flickr.com/photos/usfwspacific/,  https://medium.com/usfwspacificislands or www.twitter.com/USFWSPacific.