Historically Laysan ducks (Anas laysanensis) were found throughout the Hawaiian archipelago. They have been recorded on Laysan Island and Lisianski Island and subfossil evidence have been found on the islands of Kaua`i, O`ahu, Maui, Moloka`i, and Hawai`i (Olson and Ziegler 1995, James and Olson 1991). Due to introduced mammals, habitat degradation, and human exploitation, Laysan ducks were brought close to extinction by the early 1900s and restricted to Laysan Island. In 2004 and 2005 a founding population of 42 ducks were translocated from Laysan Island to Midway Atoll National Wildlife Refuge (Midway Atoll). Additionally, Laysan ducks (Anas laysanensis) were translocated from Midway Atoll to Kure Atoll in 2014. Over the last 15 years, Midway Atoll’s Laysan duck population has surpassed that of Laysan Island’s with some trials and tribulations along the way. Through collaborative effort with partner agencies and diligent management, Midway Atoll has overcome difficulties and enhanced the habitat to meet the needs of the Laysan duck.
Through intensive monitoring from 2007 to 2015 Reynolds et al. (2017) used these data to estimate maximum population size. Since the translocation from Laysan Island, population monitoring has included radio telemetry of translocated ducks and their offspring from 2004 to 2007, resight data from banded ducks, and standardized surveys from 2007 to 2019. A modified Chapman bias-corrected Lincoln-Peterson mark-resightings population abundance with 95% confidence intervals (CI) were created for the Laysan duck population from 2007 to 2019. Standardized surveys were not conducted in 2013, therefore no population estimate could be generated. In 2016, standardized surveys were irregular and a 95% CI could not be generated. Surveys were not conducted during winter 2016-2017; therefore the 2017 estimate is based on breeding season surveys only.
Through standardized surveys, trends in reproduction have also been observed. Total number of ducklings observed during surveys spike in May and July which is likely indicative of females raising two broods in a nesting season.
Prior to the translocation of Laysan ducks to Midway Atoll, the Refuge created manmade ponds and outplanted native species. To further improve habitat at Midway Atoll, in 2011 the Refuge received a $1 million National Wildlife Refuge System grant and matching grant of $1 million from National Fish and Wildlife Foundation to eradicate the invasive species Verbesina encelioides which covered 68% of Sand Island and 78% of Eastern Island. Removal of Verbesina has allowed for intensive habitat restoration to increase native plant cover such as kāwelu (Eragrostis variabilis), 'āweoweo (Chenopodium oahuense), 'aki'aki (Sporobolus virginicus), pōpolo (Solanum nelsonii), 'ilima (Sida fallax), and makaloa (Cyperus laevigatus). These native plants provide cover and foraging habitat for Laysan ducks. Due to the removal of Verbesina, air flow at the manmade ponds has increased and this results in them being cooler, more oxygenated, and prevents them from becoming stagnant. Verbesina removal around the ponds has also helped increase detection for avian botulism.
Makaloa (Cyperus laevigatus) in particular is an extremely advantageous native plant for Laysan ducks and Midway Atoll’s ponds. This indigenous wetland plant is used in the main Hawaiian Islands to control erosion along stream banks and provide a natural food source and cover for native water birds (University of Hawaii, 2009). Makaloa is found on mud flats, sandy coastal sites, anchialine pools, and brackish or salt water ponds throughout the Hawaiian archipelago. In the main Hawaiian Islands makaloa is used to restore native wetland habitat and wastewater treatment areas. In 2005 makaloa was collected from Laysan Island, transported via the Hokule'a (Hawaiian voyaging canoe), and introduced to Midway Atoll. This occurred in conjunction with the translocation of the critically endangered Laysan duck (Anas laysanensis). In 2018, USFWS staff noticed the clarity of seeps with makaloa was much clearer than without. Staff constructed floating islands and transplanted makaloa to the shorelines to see if it could improve water quality. Observationally, staff noticed less algal build up as well as more cover and food availability for Laysan ducks.
Avian botulism has plagued Midway Atoll with the first outbreak occurring in 2008 and since the initial outbreak, botulism cases have occurred annually. Ducks that ingest toxins produced from Clostridium botulinum causes avian botulism type C. A duck can quickly succumb to botulism toxin and provides a concentrated source for others to feed upon. This can escalate the botulism outbreak quickly with more sources of botulism being available. The first botulism outbreak started in August 2008 and resulted in 181 dead Laysan ducks (Work et al. 2010). This accounted for approximately half of the population. To mitigate outbreaks, ponds and guzzlers are checked once a week in the winter and twice a week in the summer to remove carcasses and treat infected birds. Daily surveillance occurs when botulism is detected. Other mitigation actions have included filling ponds, improving the water quality of ponds, and installing guzzlers which can be easily cleaned. The Laysan duck population can remain stable through diligence, rapid response, and constantly striving to improve wetland habitat.
Ongoing removal of invasive plant species and restoring the landscape with native plant species will benefit the Laysan duck population. The invasive house mouse (Mus musculus) may have negative impacts on Laysan ducks directly or indirectly by limitation of food sources. Mice present on Lisianski most likely accelerated their decline by competing for food and destroying vegetation cover (Olson and Ziegler 1995). The Refuge proposal (USFWS 2018) for removal of the house mouse will allow for natural regeneration of native plants thus providing more food and cover for Laysan ducks. The mouse eradication also allows opportunities to investigate the impacts of mice pre– and post– eradication which includes native plant regeneration and duck diet analysis. After the mouse eradication this could prove to be an ideal time to reassess the population models due to the drastic ecosystem changes. In addition further understanding of duckling and adult survivorship would benefit this species.
Mahalo Nui Loa!
Midway Atoll NWR’s countless volunteers and Kupu interns
USFWS current and previous staff
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Hawaii Wildlife Center
James HF, and SL Olson (1991) Descriptions of thirty-two new species of birds from the Hawaiian Islands. Part II. Passeriformes. Ornithological Monographs 46:1- 88.
Olson, SL, and AC Ziegler (1995) Remains of land birds from Lisianski Island, with observations on the terrestrial avifauna of the northwestern Hawaiian Islands. Pacific Science 49:111-125.
Reynolds, MH, KN Courtot, and JS Hatfield (2017) How many Laysan Teal Anas Lasysanensis are on Midway Atoll? Methods for monitoring abundance after reintroduction. Wildfowl 67:60-71.
University of Hawaii (2009) Native Plants Hawaii: Cyperus laevigatus. Retrieved June 20, 2019 from http://nativeplants.hawaii.edu/plant/view/Cyperus_laevigatus
USFWS (2018) Midway Seabird Protection Project: Final Environmental Assessment and Project Plan. Retrieved June 27, 2019 from https://fws.maps.arcgis.com/apps/MapSeries/index.html?appid=e7bbcf5c95804186902ef938f1c020f2
Work, TM, JL Klavitter, MH Reynolds, and D Blehert (2010) Avian botulism: a case study in translocated endangered Laysan ducks (Anas laysanensis) on Midway Atoll. Journal of Wildlife Diseases 46:499-506.