Science Center Objects

The Honolulu Field Station provides routine diagnostic support to state and federal agencies in order to determine cause of death in endangered and threatened native birds in Hawaii, US territories, and affiliated states in the Pacific.   These activities have resulted in information that was important in the recovery of several species of endangered birds such as Laysan ducks, Nihoa millerbirds, Hawaiian ducks, and Hawaiian crows.

Nene adults and goslings in a grassy field

A mating pair of adult nēnē (Branta sandvicensis) keep a close watch on three young goslings. An endangered species and the state bird of Hawai‘i, nēnē are affected by the parasite Toxoplasma gondii.(Credit: USGS.)

Surveillance  

Doing necropsies on birds to determine cause of death permits us to keep tabs on the health of wild bird populations and allows for detection of new threats.  For instance, the discovery of Toxoplasma gondii, a parasite transmitted by feral cats, as a cause of native Hawaiian crow declines in mid-elevation forests on the Island of Hawaii prompted removal of remnant crows from the wild.  Present reintroductions of crows to their native range are coupled with aggressive management of feral cats to reduce impacts of this parasite to newly released crows.  Likewise, the discovery of botulism, a bacteria-produced toxin in wetlands, as a cause of death in endangered waterfowl has resulted in management of environmental factors to reduce the impacts of this toxin on Hawaiian wetlands.

Research

Mariana crows are one of the most endangered crows in the world.  Populations of this bird were historically on Rota and Guam but were extirpated from the latter because of predation by the brown tree snake.  Since then, the only remnant population of this bird is on Rota where numbers have declined over 90% since the mid-1980s for unknown reasons.  Introduced predators like rats, feral cats, and monitor lizards, as well as habitat destruction, human persecution, and disease are suspected causes of this decline.  Crow habitat on Rota has been protected since 1994, and removal of non-native predators from core breeding habitat began in 2012; however high rates of mortality continue to affect the population.  

Mariana Crow, Rota

Mariana crows. (Credit: Phillip Hannon, University of Washington Rota Avian Behavioral Ecology Program.)

We are working closely with the CNMI Department of Fish & Wildlife, the US Fish and Wildlife Service, and the University of Washington to better understand actual causes of crow declines.   This process is complicated by the remoteness of the island, difficulty in detecting dead birds and shipping them to laboratories to determine cause of death.  Recently, however, due to concerted efforts by field biologists on Rota, the HFS has received carcasses of immature Mariana crows in suitable post-mortem condition.  Necropsies of crows have revealed a consistent pattern of massive inflammation of the liver and lung suggesting that crows might be dying from an infectious disease or, less plausibly, some sort of toxin.  An infectious disease amongst immature Mariana crows may thus explain why the birds have been declining on Rota.  HFS is currently collaborating with a variety of laboratories to determine what might be causing these lesions in immature Mariana crows.   

Resources

Seabird Necropsy Manual