Geology topics

Research about Laysan Island

Source-linked reports with geographic coverage including Laysan Island.

3 recordsLinked to original sources

USGS2005

Mortality in the endangered Laysan teal, Anas laysanensis: conservation implications

The Laysan Teal Anas laysanensis is an endangered anatid of the Hawaiian Islands, currently restricted to an emergent atoll, Laysan Island. Laysan Island lacks terrestrial mammalian predators, which permits the examination of mortality rates and causes without the anthropogenic effects of introduced predators. Mass and morophometrics were measured during the colour-marking of 297 Laysan Teal between 1998 and 2001. Intensive mark-resighting and recovery methods were used to estimate adult and juvenile mortality. One hundred and nineteen carcasses were collected on Laysan between 1998 and 2003, and systematic gross and microscopic examinations were undertaken on 63 of these. Causes of mortality were categorised as trauma, emaciation, miscellaneous or undetermined. Annual adult mortality rates were low, 0.05-0.10 (s.e. <0.01), but duckling mortality was much higher, varying from approximately 0.7-0.9 during 1998-2000 and 2003. Body condition of both sexes deteriorates during the breeding season, and most adult mortality (88%) occurred during or post-breeding (May-October). Cause of mortality was determined via necropsy in 22 ducks. Of three adults, one died from bacterial infections, one was egg bound, and one died from botulism concomitant with nematode infestation. Fourteen ducklings died from acute trauma, four from emaciation sometimes associated with nematode infection, and one from bacterial pneumonia Trauma is a significant factor in Laysan duckling mortalities, and elucidating the cause of and preventing such trauma may allow for management measures to enhance duckling survivability. High duckling mortality rates and emaciation also indicate that habitat on Laysan Island may have limited capacity to support broods.

Hawai'i↗

USGS2004

Habitat use and home range of the Laysan Teal on Laysan Island, Hawaii

The 24-hour habitat use and home range of the Laysan Teal ( Anas laysanensis ), an endemic dabbling duck in Hawaii, was studied using radio telemetry during 1998-2000. Radios were retained for a mean of 40 days (0-123 d; 73 adult birds radio-tagged). Comparisons of daily habitat use were made for birds in the morning, day, evening, and night. Most birds showed strong evidence of selective habitat use. Adults preferred the terrestrial vegetation (88%), and avoided the lake and wetlands during the day. At night, 63% of the birds selected the lake and wetlands. Nocturnal habitat use differed significantly between the non-breeding and breeding seasons, while the lake and wetland habitats were used more frequently during the non-breeding season. Most individuals showed strong site fidelity during the study, but habitat selection varied between individuals. Mean home range size was 9.78 ha ( SE ± 2.6 ) using the fixed kernel estimator (95% kernel; 15 birds, each with >25 locations). The average minimum convex polygon size was 24 ha ( SE ± 5.6 ). The mean distance traveled between tracking locations was 178 m ( SE ± 30.5 ), with travel distances between points ranging up to 1,649 m. Tracking duration varied from 31-121 days per bird (mean tracking duration 75 days).

Hawaii↗

USGS2004

Mortality in Laysan ducks (Anas laysanensis) by emaciation complicated by Echinuria uncinata on Laysan Island, Hawaii, 1993

In November 1993, unusual mortality occurred among endangered Laysan ducks on Laysan Island, one of the remote refugia of the Northwestern Hawaiian Islands National Wildlife Refuge (USA). Ten live ducks were emaciated, and blood samples documented anemia, heterophilia, and eosinophilia. Pathology in 13 duck carcasses revealed emaciation, marked thickening of the proventricular wall, abundant mucus, and nodules in the gastrointestinal tract. Histology revealed granulomata associated with nematodes in the proventriculus, small intestines, and body walls of nine of 10 ducks examined on histology. We suspect that low rainfall and low food abundance that year contributed to enhanced pathogenicity of parasite infection, either through increased exposure or decreased host resistance. Because the Laysan duck is found only on Laysan island and is critically endangered, translocation of this species to other islands is being considered. Given that we have not seen pathology associated with Echinuria spp. in native waterfowl on other Hawaiian Islands and given the parasite's potential to cause significant lesions in Laysan ducks, it will be important to prevent the translocation of Echinuria spp.

Hawai'i↗