Draft Revised Recovery Plan for 

the Laysan Duck 

(Anas laysanensis) 

(August 2004) 

(Original approved 17 December 1982) 

Region 1 

U.S. Fish and Wildlife Service 

Portland, Oregon 

Approved: XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

 Regional Director 

Date: XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
Laysan Duck Draft Revised Recovery Plan, August 2004. 

i

DISCLAIMER 

Recovery plans delineate reasonable actions that are believed to be required to 

recover and/or protect listed species. Plans are published by the U.S. Fish and Wildlife 

Service, and sometimes prepared with the assistance of recovery teams, contractors, State 

agencies, Tribal agencies, and others. The necessary funds to attain objectives identified 

in a recovery plan are subject to budgetary and other constraints affecting the parties 

involved, as well as the need to address other priorities. Costs indicated for action 

implementation and time for achievement of recovery are only estimates and subject to 

change. Recovery plans do not necessarily represent the views nor the official positions 

or approval of any individuals or agencies involved in plan formulation, other than the 

U.S. Fish and Wildlife Service. Recovery plans represent the official position of the U.S. 

Fish and Wildlife Service only after they have been signed by the Director or Regional 

Director as approved. Approved recovery plans are subject to modification as dictated by 

new findings, changes in species status, and the completion of recovery actions. 

Literature citation of this document should read as follows: 

U.S. Fish and Wildlife Service. 2004. Draft Revised Recovery Plan for the Laysan Duck 

(Anas laysanensis). U.S. Fish and Wildlife Service, Portland, Oregon. vii + 94 pp. 

Electronic copies of this document will be made available at: 

• http://pacific.fws.gov/ecoservices/endangered/recovery/default.htm 

• http://endangered.fws.gov/recovery/index.html 
Laysan Duck Draft Revised Recovery Plan, August 2004. 

ii

ACKNOWLEDGMENTS 

This revision of the Laysan Duck recovery plan was drafted for the U.S. Fish and 

Wildlife Service by Michelle H. Reynolds and George L. Ritchotte of the U.S. 

Geological Survey Pacific Islands Ecosystem Research Center. Helen James of the 

Smithsonian Institution Museum of Natural History provided information about the 

distribution of subfossil remains. Maps were produced by Ron Salz and Rod Lowe, 

Pacific Islands Fish and Wildlife Office. Final modifications, editing, and formatting 

were completed by Holly Freifeld, Pacific Islands Fish and Wildlife Office. Reviews of 

earlier drafts of this document were kindly provided by Paul Banko, Colleen Henson, 

Paul Henson, John Klavitter, Marie Morin, Chris Swenson, Eric VanderWerf, Ron 

Walker, Jeff Walters and the Virginia Polytechnic Institute and State University’s Avian 

Ecology Lab, and Marilet Zablan. Additional comments were provided by Alan 

Lieberman (Hawaii Endangered Bird Conservation Program), and Thierry Work 

(National Wildlife Health Research Center). 
Laysan Duck Draft Revised Recovery Plan, August 2004. 

iii

EXECUTIVE SUMMARY 

Current Species Status: The Laysan duck (Anas laysanensis), also called the Laysan 

teal, is an endemic Hawaiian species and has been federally listed as endangered since 

1967 (U.S. Fish and Wildlife Service [USFWS] 1967). The Laysan duck currently has 

the most restricted range of any duck in the world, with a single remaining population on 

Laysan Island in the Northwestern Hawaiian Islands. The species was extirpated from 

most other islands of the Hawaiian archipelago after the arrival of the first humans about 

1,500 years ago. To date, Laysan duck bones have been found from extirpated 

populations on the islands of Hawai`i, Maui, Moloka`i, O`ahu, Kaua`i, and Lisianski. 

The total estimated population size on Laysan Island has fluctuated from 7 to 688 adult 

birds in the last century. The most recent (2001) population estimate of adult birds is 

459. Viability models for small populations of isolated species predict a high risk of 

extinction due to catastrophic, environmental, genetic, and demographic stochasticity. 

Habitat Requirements: The habitat requirements of the Laysan duck include 

vegetation in which to take cover, an abundant prey base of invertebrates, a source of 

fresh water, and protection from mammalian predators. On Laysan Island, the ducks use 

all available habitats: upland vegetation, ephemeral wetlands, freshwater seeps, mudflats, 

the hypersaline lake, and coastal areas. The ducks feed on wetland and terrestrial 

invertebrates, seeds, and succulent plants. Ducklings have more restrictive requirements 

than adults because of their high nutritional requirements for growth and initial inability 

to process saltwater. Duckling activities are concentrated near sources of fresh water 

with nearby cover and high prey densities. 

Historically, this species occurred in a diverse range of habitats on Hawaiian 

islands other than Laysan. Paleoecological evidence indicates it likely was a habitat 

generalist. On high elevation islands, ducks once were found both in upland forests far 

from standing water and in coastal wetlands. The duck’s diet probably consisted mainly 

of arthropods from the forest floor and wetlands. 

Limiting Factors: Five factors are considered in the decisions to list, delist, or 

reclassify a species. These factors are: 

A – The present or threatened destruction, modification, or curtailment of its habitat 

or range; 

B – Overutilization for commercial, recreational, scientific, or educational purposes; 

C – Disease or predation; 

D – Inadequacy of existing regulatory mechanisms; and 

E – Other natural or man-made factors affecting its continued existence. 
Laysan Duck Draft Revised Recovery Plan, August 2004. 

iv

Prehistoric populations of the Laysan duck on the Main Hawaiian Islands were 

most likely extirpated by a combination of human hunting, habitat destruction or 

degradation, and predation by introduced mammals, especially rats (Rattus exulans). 

Introduced mammalian predators would pose the most severe threat to new populations 

of Laysan ducks in the Main Hawaiian Islands (Factor C). Alien species indirectly 

harmful to the historical Laysan and/or extirpated Lisianski populations through habitat 

alteration include rabbits, mice, invasive weeds, and possibly predatory insects (Factor 

A). Storms, drought-related food reductions, disease, and limited carrying capacity are 

among the factors limiting the Laysan population today (Factors C and E). High 

duckling mortality in 1999 and 2000 suggests a lack of sufficient brood rearing habitat on 

Laysan (Factor A). Inbreeding depression may be a limiting factor, but additional 

information is required to evaluate this possibility (Factor E). Long-term threats include 

the accelerated filling of Laysan’s freshwater seeps and lake (Factor A); these changes 

result from 20th century devegetation of the islands by rabbits and may be exacerbated by 

sea level rise due to global warming. Sea level rise resulting from global climate change 

may result in the loss of terrestrial habitat (Factor E). The actions proposed in this plan 

are designed to address these threats to the Laysan duck and to reestablish multiple 

populations on additional islands in order to achieve recovery objectives for the species. 

Recovery Priority Number: The recovery priority number for the Laysan duck is 2 

on a scale of 1C (highest) to 18 (lowest), reflecting a high degree of threat, high potential 

for recovery, and its status as a full species. 

Recovery Goal: Conserve and recover the Laysan duck in order to downlist to 

threatened status, with the ultimate goal of removing the Laysan duck from the Federal 

list of endangered species (delisting). 

Recovery Objective: Restore the Laysan duck to multiple self-sustaining populations 

in suitable habitats in the Northwestern and Main Hawaiian Islands such that the 

protections of the Endangered Species Act are no longer necessary. 

Recovery Strategy: Recovery of the Laysan duck focuses on the following actions: 1) 

management to reduce risks to the Laysan Island population; 2) protection and 

enhancement of suitable habitat; and 3) actions to reduce or eliminate threats sufficient to 

allow successful reestablishment of additional wild populations. 

Recovery Criteria: At this time we have developed only interim downlisting criteria 

for the Laysan duck due to the data limitations and potential uncertainties associated with 

attempting to define realistic criteria for delisting, particularly in regard to target 

population sizes. Because our knowledge of Laysan duck population biology and 

ecology is restricted to observations from the unique environment of Laysan Island, we 
Laysan Duck Draft Revised Recovery Plan, August 2004. 

v

currently have no reliable biological basis for setting target population sizes for delisting 

on other islands with very different habitats and potential threats. Delisting criteria, when 

developed, must be based on new information that can only be accumulated as we begin 

to implement the recovery actions outlined in this plan and learn about the population 

dynamics and growth rates of Laysan ducks in new habitats on islands other than Laysan. 

For downlisting, the following conditions must be met: 

Criterion 1. The Laysan Island population is stable or increasing (finite rate of 

population growth or λ greater than or equal to 1.0) when averaged over a continuous 

period of at least 15 years. 

Criterion 2. A total of at least 920 potentially breeding adult birds exist in at least 5 

stable or increasing populations on a combination of predator-free Northwestern 

Hawaiian Islands (including Laysan) and predator-controlled sites on Main Hawaiian 

Islands. The population on Laysan Island should remain at a level of from 400 to 500 

birds; the remaining 4 or more newly established populations should occur on a 

combination of predator-free Northwestern Hawaiian Islands and predator-controlled 

sites on the Main Hawaiian Islands, and should number approximately 130 breeding 

adult birds each (depending on the size of the habitat available on each island). 

Criterion 3. A successful captive or semi-captive breeding program is established using 

wild source eggs. These captive populations are managed primarily for 

reintroductions to the Main Hawaiian Islands. 

Criterion 4. A plan for achieving gene flow between wild source populations through 

long-term inter-island translocations is developed and implemented. 

Criterion 5. Island-specific management plans for each population are created that 

identify actions (such as supplementation, habitat improvement and predator control) 

sufficient to reduce threats and increase the populations to recovery levels. 

Date of Recovery: Downlisting could occur by 2019 if criteria have been met. Due 

to the many uncertainties regarding the data needed to develop sound delisting criteria, 

we have determined that further research is needed before such criteria may be defined, 

therefore at this time we cannot estimate when delisting might occur. 

Total Estimated Cost of Recovery: The estimated cost for recovery actions over 

the next 5 years is $9,325,000. 
Laysan Duck Draft Revised Recovery Plan, August 2004. 

vi

TABLE OF CONTENTS 

 

EXECUTIVE SUMMARY....................................................................................................iii

LIST OF TABLES.................................................................................................................vii

LIST OF FIGURES...............................................................................................................vii

I. INTRODUCTION AND OVERVIEW ............................................................................. 1

A. Status Overview and Structure of the Recovery Plan ...................................................1

B. Species Description and Taxonomy..............................................................................4

C. Island History and Habitat.............................................................................................6

1. Laysan Island...........................................................................................................6

2. Lisianski Island .......................................................................................................7

3. Prehistoric Habitat...................................................................................................8

D. General Biology and Ecology.....................................................................................10

1. Habitat Use............................................................................................................10 

2. Foraging ................................................................................................................14 

3. Reproductive Biology............................................................................................20 

4. Demography ..........................................................................................................22 

5. Population and Species Viability ..........................................................................25 

E. Reasons for Decline and Current Threats.....................................................................30

1. History of Decline: Range Contraction and Reduced Numbers............................31 

2. Current Threats.......................................................................................................32 

II. RECOVERY STRATEGY .............................................................................................. 38

A. Past and Current Conservation Measures ....................................................................38

1. Laysan Duck Population Monitoring ....................................................................38 

2. Ecosystem Conservation and Monitoring .............................................................39 

3. Captive Populations...............................................................................................40 

4. Pearl and Hermes Reef Translocation ...................................................................41 

B. Translocation .............................................................................................................41

1. Justification for Immediate Translocation.............................................................42 

2. Hybridization and Introgression............................................................................42 

3. Source Population .................................................................................................43 

4. Transfer Population ................................................................................................44 

5. Selecting and Evaluating the Release Site.............................................................45 

6. Prospects for Reintroduction of Captive Birds......................................................49 

III. RECOVERY CRITERIA AND ACTIONS................................................................. 51

A. Goal and Objectives....................................................................................................51

B. Recovery Criteria ........................................................................................................51

1. Downlisting Criteria..............................................................................................52 

2. Rationale for Downlisting Criteria ........................................................................53 

C. Outline of Recovery Actions .......................................................................................55

D. Recovery Action Narrative .........................................................................................56

IV. IMPLEMENTATION SCHEDULE FOR 2004 TO 2008 .......................................... 64

V. REFERENCES ................................................................................................................. 70
Laysan Duck Draft Revised Recovery Plan, August 2004. 

vii

A. Literature Cited ...........................................................................................................70

B. Personal Communications............................................................................................82

VI. APPENDICES ................................................................................................................. 83

Appendix 1. Habitat assessments of possible translocation sites for the 

Laysan duck ........................................................................................83

Appendix 2-A. Assets of preferred sites evaluated for proposed reintroduction 

of the Laysan duck ..............................................................................86

Appendix 2-A Liabilities of preferred sites evaluated for proposed 

reintroduction of the Laysan duck ......................................................87

Appendix 3. VORTEX population viability analyses: parameters and 

conditions used and summary of results .............................................89

 

LIST OF TABLES 

Table 1. Frequency of occurrence of taxa identified in Laysan duck fecal samples 

(proportions of samples with prey types) collected on Laysan Island at 

the lake in 1985 (Lenz and Gagne 1986) and 1998-2000 at both the 

lake and terrestrial habitats (Reynolds 2002). .................................................. 16

Table 2. Estimates of Laysan duck population size on the island of Laysan using 

line-transect and mark-resight methods............................................................ 23

Table 3. Implementation schedule for the draft revised Laysan duck recovery plan 

2004 to 2008..................................................................................................... 66 

LIST OF FIGURES 

Figure 1. Map of the Hawaiian Islands, with a detail of Laysan Island . . . . . . . . . . . 2

Figure 2. Map of the Hawaiian Islands showing the Laysan duck’s known former 

range, current range, and site of unsuccessful translocation attempt . . . . . . 9

Figure 3. Map of habitat zones on Laysan Island . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Figure 4. Time activity budget of Laysan teal in habitat zones of Laysan Island . . . . 12

Figure 5. Seasonal brine fly abundance reported as monthly mean with standard 

error, and first brood sightings of Laysan ducks 1998 to 1999 . . . . . . . . . . 18

Figure 6. Causes of mortality for Laysan duck adults and ducklings found dead 

1993 to 2001 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Figure 7. Laysan duck carcass age class breakdown from 1998 to 2001 . . . . . . . . . . 26
Laysan Duck Draft Revised Recovery Plan, August 2004. Part I: Introduction and Overview. 

1

I. INTRODUCTION AND OVERVIEW 

A. Status Overview and Structure 

of the Recovery Plan 

The Hawaiian Archipelago is the 

world’s most isolated group of islands. 

This isolation has produced a high level 

of endemism in the flora and fauna and 

many groups exhibit outstanding 

examples of adaptive radiation (Scott et 

al. 1986, Banko et al. 2001). A total of 

142 endemic (i.e., found only in 

Hawai`i) species and subspecies of birds 

known from collected specimens or 

nonmineralized fossils have been 

described from the Hawaiian Islands 

(James and Olson 1991, Olson and 

James 1991, Giffen 1993, Pyle 1997). 

Following human colonization of the 

Hawaiian Islands in approximately 400 

A.D., endemic species declined 

markedly in numbers and distribution 

(James and Olson 1991, Olson and 

James 1991, Banko et al. 2001). Of the 

142 endemic bird species and 

subspecies, about 95 have been 

extirpated since the advent of human 

colonization (Banko et al. 2001). The 

remaining endemic taxa are also 

vulnerable to extinction with 32 taxa 

listed as endangered or threatened, 

including 30 landbirds and 2 seabirds. 

In addition to birds, Hawai`i’s 

remaining flora and fauna are also 

vulnerable to extinction. Hawai`i is 

home to 322 of the 1,258 animal and 

plant species federally listed as 

threatened or endangered nationwide, 

roughly 25 percent of all listed species 

(U.S. Fish and Wildlife Service 

[USFWS] 2002). 

Island species in general and 

Hawaiian species in particular are highly 

vulnerable to human disturbance. In 

addition to the birds lost during the 

initial human colonization of the 

Hawaiian Islands, 24 more species or 

subspecies of Hawaiian birds have 

become extinct since the arrival of 

Captain Cook in 1778. Of the 30 

species or subspecies of birds currently 

listed as threatened or endangered, 10 

may already be extinct. These numbers 

indicate that roughly half of the 

Hawaiian land and water birds that were 

present at the time of European contact 

have disappeared in the last two 

centuries (Scott et al. 2001). 

The Laysan duck (Anas laysensis), 

also known as the Laysan teal, is one of 

six extant waterbird species that are 

endemic to Hawai`i. The Laysan duck 

currently has the most restricted range 

of any duck in the world, with a single 

population estimated at 459 adult birds 

on the small island of Laysan in the 

Northwestern Hawaiian Islands (Figure 

1). In recorded history, only one other 

population of Laysan ducks was known, 

on adjacent Lisianski Island (Olson and 

Ziegler 1995). However, that 

population had been extirpated by the 

early 1800’s, leaving only the remnant 

population on Laysan Island. 
!

! !

!

!

!

!

!

! !

Oa

Ka

Niihau

Nihoa Island

Tern Island at Necker Island

French Frigate Shoals

Gardner Pinnacles

Maro Reef

Laysan Island

Lisianski Island

Pearl and Hermes Reef

Midway Atoll NWR

Kure Atoll

0 

250 

0 500 250 

0 1 0.5 Miles

0 1 0.5 Kilometers 2

2

Figure 1. Map of the Hawaiian Islands, with a detail of La
Laysan Duck Draft Revised Recovery Plan, August 2004. Part I: Introduction and Overview. 

 3

We have only recently learned 

through subfossil evidence that the 

Laysan duck once occurred throughout 

the Main Hawaiian Islands; to date, 

bones have been found on the islands of 

Hawai`i, Maui, Moloka`i, O`ahu, and 

Kaua`i (James and Olson 1991, Cooper 

et al. 1996). The extirpation of the 

Laysan duck from the Main Hawaiian 

Islands in prehistory likely resulted from 

a combination of rats (Rattus exulans), 

habitat loss, and predation by humans, 

and possibly introduced dogs (Canis 

familiaris) and pigs (Sus scrofa). 

 The Laysan duck was federally 

listed as endangered in 1967 (USFWS 

1967). Sixty-five of the world’s 231 

species of waterfowl are endangered; of 

these, the Laysan duck is one of the 

most critically endangered (Black 1998). 

The Laysan duck has a recovery priority 

number of 2. Recovery priority 

numbers are assigned to a species based 

on degree of threat, recovery potential, 

taxonomic status, and conflict with 

human activities. Numerical ranks 

range from 1 to 18, with a letter 

designation of “C” indicating conflict 

with human economic activities. The 

highest priority is 1C; the lowest priority 

is 18 (USFWS 1983a,b). The Laysan 

duck’s recovery priority number of 2 

indicates that it faces a high degree of 

threat, has a high potential for recovery, 

its taxonomic rank is a full species, and 

it is generally not in conflict with human 

activities. Critical habitat has not been 

designated for the Laysan duck. 

The strategy to recover the Laysan 

duck consists of maintaining the 

population on Laysan, reducing or 

eliminating the current threats to the 

species, and reestablishing populations 

on several other islands at levels capable 

of withstanding random environmental 

and demographic fluctuations. 

Populations large enough to tolerate 

environmental uncertainties will also be 

able to withstand demographic 

uncertainties. Based on the results of 

population viability analyses, we 

estimate that the establishment of 

multiple populations on a combination 

of Northwestern and Main Hawaiian 

islands, managed to ensure periodic 

gene flow between them, will ensure the 

long-term persistence of the Laysan 

duck. 

The original recovery plan for the 

Laysan duck was issued in 1982 

(USFWS 1982). In the subsequent 20+ 

years, we have learned a great deal 

about this species. In addition to 

providing a recovery strategy for the 

Laysan duck, this revised recovery plan 

also provides a synthesis of our current 

knowledge of the ecology of the duck 

and its recent and prehistoric 

distribution. 

This recovery plan is divided into 

four main parts. Part I provides an 

overview of the biology of the species, 

the history of its decline, and current 

threats to its persistence. Part II 

summarizes both past and current 

conservation efforts for the species and 

outlines the recovery strategy. Parts III 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part I: Introduction and Overview. 

 4

and IV present the recovery criteria and 

actions needed to achieve recovery, 

including the implementation schedule, 

with emphasis on actions needed to 

achieve interim recovery goals within 

the next 5 years. This structure reflects 

the need for effective adaptive 

management in advancing the recovery 

of the Laysan duck, as many variables 

remain unknown and long-term 

planning without inherent flexibility is 

unlikely to succeed. These short-term 

implementation plans will be prepared 

every 5 years to reflect the knowledge 

gained and refine the management 

program accordingly to maximize the 

success of the Laysan duck recovery 

program. 

B. Species Description and 

Taxonomy 

The Laysan duck (American 

Ornithologists’ Union 1998), also 

known as the Laysan teal, is a small 

(38.1 to 43.2 centimeters [15 to 17 

inches] in length, weight 420 to 500 

grams [14.8 to 17.6 ounces]), mostly 

chocolate brown duck with contrasting 

bi-colored body feathers (USFWS 1982, 

Moulton and Marshall 1996). It has an 

iridescent purplish-green speculum 

(wing patch) and a prominent white eye 

ring. There is considerable individual 

variation in plumage. The eye ring is 

nearly absent on juvenile birds, and 

becomes more extensive and irregular in 

adults. Leucistism, or extensive white 

feathering, is common on the head and 

neck, especially in birds older than 3 

years. The plumage of both sexes is 

quite similar, but bill and leg coloring 

can be used to distinguish sexes. In 

males, the short and spatulate bill is 

olive-green with black blotches along 

the maxilla (upper half of the bill). 

Females have a slightly shorter, paler 

orange bill with variable black mottling. 

Both sexes have dull orange legs, 

although the male’s legs typically are 

brighter (Moulton and Marshall 1996). 

Mass fluctuates significantly with 

season (Reynolds 2002). Males are 

heavier than females in most seasons, 

but females tend to be heavier than 

males during the pre-breeding and 

laying stages. Other morphometric 

characteristics (wing chord, tarsus, and 

bill length) are on average slightly larger 

for males (Moulton and Marshall 1996). 

As with other waterfowl, Laysan 

ducks molt all of their flight feathers at 

the same time and are incapable of flight 

for a period of time until the new 

feathers grow in. On Laysan, this molt 

typically occurs between July and 

August for males and between July and 

September for females (Moulton and 

Marshall 1996). For female ducks, the 

molt usually occurs after brood rearing. 

The timing of the molt is variable, as is 

the timing for breeding. The occurrence 

of this molt should be considered in 

recovery efforts; although Laysan ducks 

are always vulnerable to terrestrial 

predators, this vulnerability is most 

likely heightened during the molt. 

Ducklings are precocial (hatched 

with down and eyes open; able to walk, 

but are led by hen and taught how and 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part I: Introduction and Overview. 

 5

where to forage) and very large relative 

to adults, weighing 22 to 30 grams (0.77 

to 1.05 ounces) newly hatched. They 

have dark brownish-yellow plumage 

with inconspicuous markings. The chin 

is somewhat lighter; the forehead, lores 

(area between the base of the bill and 

the eye), and ear patches are darker. 

Feathers on the cheeks, breast, belly, 

around the wing patches and around the 

eye are a grayish-yellow. Most 

ducklings have an eye-stripe, but it is 

not easily distinguished from afar. The 

toes and lower legs are olive-brown, 

with bluish gray webs. Juveniles fledge 

after obtaining flight feathers at 55 to 65 

days of age (Moulton and Marshall 

1996). 

The Laysan duck is unique 

behaviorally, genetically, and in its life 

history traits. It is a relatively longlived species (12 years in the wild, 18 in 

captivity; Moulton and Weller 1984, 

Reynolds and Kozar 2000a) with a low 

reproductive rate (clutch size averages 

3.8 eggs). The Laysan duck is mostly 

nocturnal in its habits, feeds primarily 

on insects, and is very sedentary and 

terrestrial for a waterfowl species. 

Having evolved with avian predators 

instead of mammalian predators, the 

ducks are more likely to walk than fly, 

and when startled they tend to freeze 

rather than flush. These behaviors make 

them vulnerable to introduced 

mammalian predators, exploitation by 

humans, and may partially explain their 

extirpation from the Main Hawaiian 

Islands during the period of human 

colonization. 

Laysan ducks exhibit several 

morphological adaptations to a largely 

terrestrial existence. They have a 

shorter middle toe, disproportionately 

long femur, and pelvic differences 

compared to continental dabbling ducks. 

They are also smaller, have shorter 

wings with fewer primaries, and 

moderate flight muscle reduction 

relative to mallards (Anas 

platyrhynchos; Livezey 1993, Moulton 

and Marshall 1996). 

The Laysan duck is a taxonomically 

distinct species in the waterfowl family 

(Anatidae: Tribe Anatini). There are 15 

species of dabbling ducks endemic to 

islands (Weller 1980), suggesting that 

the ducks that colonized these islands 

originally were capable of long-distance 

flight. Once thought to be closely 

related to the North American mallard 

group and the Hawaiian duck or koloa 

(Anas wyvilliana), new genetic evidence 

reveals that the Laysan duck’s 

divergence from the koloa/mallard 

lineage is robust (Rhymer 2001), and 

represents a separate colonization of 

Hawai`i. From a phylogenetic and 

biogeographic analysis, Johnson and 

Sorenson (1999) reconstructed the 

origins for the Laysan duck, and 

concluded that its ancestor, an ancient 

member of the mallard clade, was of 

Southern Hemisphere, East 

Asian/Pacific origins. 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part I: Introduction and Overview. 

 6

C. Island History and Habitat 

1. Laysan Island 

Laysan lies 1,463 kilometers (909 

miles) northwest of Honolulu and is 

accessible only by boat (Figure 1). 

Although feather collectors, seal and 

turtle hunters, and other mariners visited 

the island, there is no evidence that 

Laysan was inhabited before guano 

miners established a camp in 1893 (Ely 

and Clapp 1973). A small U.S. Fish and 

Wildlife Service field camp exists on 

Laysan Island today. 

Covering 415 hectares (1,025 acres), 

Laysan is the largest of the 

Northwestern Hawaiian Islands. It is 

roughly rectangular in shape, 

approximately 3 kilometers (1.9 miles) 

long from north to south and 1.5 

kilometers (0.9 miles) east to west. The 

island is made up of 187 hectares (462 

acres) of vegetated habitat and 105 

hectares (259 acres) of interior lake and 

mudflat area (Morin 1992). The 

remaining area consists of coastal dune 

and beach (Moulton and Marshall 

1996). The one large interior lake is 

characterized by high salinity, high 

nutrient content, and low species 

diversity. The lake’s salinity is 3 to 4 

times oceanic salinity. Salt tolerant 

species dominate the lake’s biota. The 

lake supports algal growth (Dunaliella

spp.), dense populations of brine shrimp 

(Artemia franciscana) and brine flies 

(Scatella sexnotata; Caspers 1981). The 

lake varies in size and depth seasonally. 

Its maximum depth was 6.5 meters (21 

feet) in 1984 (USFWS data); in the early 

20th century the lake was much deeper 

than it is today. 

The island’s highest point is 12 

meters (39 feet) above sea level (Morin 

and Conant 1998). There are coastal 

reef flats and tide pools around the 

perimeter. Fresh and brackish (0.0 to 

3.0 grams salt per 100 grams water) 

groundwater seeps occur in the interior 

of the island surrounding the lake and at 

several locations on the coast. In 1998, 

22 seeps were identified in the interior 

of Laysan surrounding the lake. During 

drought conditions, most seeps are 

below ground and inaccessible to the 

ducks (Reynolds 2002). 

Vegetation associations form 

concentric bands around the island. 

Scattered ground cover dominated by 

Nama sandvicensis (nama) is found 

closest to the coast. Moving inland, one 

finds vegetative associations that 

include coastal shrubs (Scaevola sericea 

[naupaka]), interior bunchgrasses 

(Eragrostis variabilis [kawelu]), shrubs 

(Scaevola sericea, Pluchea indica 

[Indian fleabane], and Chenopodium 

oahuense [aweoweo]), vines (Ipomoea 

pes-caprae [beach morning glory] or

Sicyos maximowiczii [anunu], S. 

pachycarpus, or S. semitonsus), and 

matted vegetation and sedges (Sesuvium

portulacastrum [akulikuli] and Cyperus

laevigatus [makaloa]) (Newman 1988, 

Morin 1992). Rainfall averaged 79 

centimeters (31.1 inches) per year from 

1992 to 2000 (range 38 to120 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part I: Introduction and Overview. 

 7

centimeters [15 to 47 inches] per year; 

USFWS data). 

Laysan Island is an important 

nesting colony for several million 

seabirds. President Theodore Roosevelt 

declared the island a bird reserve in 

1909. Today, Laysan is protected as 

part of the Hawaiian Islands National 

Wildlife Refuge, is designated as a 

National Research Reserve, and is part 

of a Coral Reef Reserve (USFWS 1982, 

National Oceanic and Atmospheric 

Administration [NOAA] 2001). 

Although Laysan today is 

dominated by native plants and animals 

and is among the most healthy of 

Hawaiian ecosystems, since human 

contact in the late 19th century the island 

has undergone massive changes from 

which it is still recovering. Historical 

accounts from the end of the 1800’s 

described the native flora and fauna in 

some detail (Morin and Conant 1998, 

Schauinsland 1899 in Rauzon 2001). 

Sandalwood trees (Santalum ellipticum), 

native palms (Pritchardia spp.), and 

grasses (Eragrostis variabilis and 

Cenchrus agrimonioides 

[kamanomano]) covered the island, but 

some of these are missing today. 

Seabirds, land birds, seals, and turtles 

were much more abundant. The 

introduction of rabbits (Oryctolagus 

cuniculus) around 1903 altered the floral 

and faunal composition of the island 

drastically. The seabirds recovered 

following the eradication of the rabbit 

population 20 years later, but 3 of 5 land 

birds went extinct (the Laysan rail, 

Porzana palmeri; the Laysan millerbird, 

Acrocephalus familiaris; and the Laysan 

honeycreeper, Himatione sanguinea 

freethii), as did 10 species of plants and 

numerous invertebrates, most of which 

were associated with host plants that 

disappeared (Butler and Usinger 1963, 

Ely and Clapp 1973, Asquith 1994). 

Humans have brought many plant and 

invertebrate species, notably Cenchrus

echinatus, a noxious sandbur grass, and 

ants (family Formicidae). Prior to the 

introduction of rabbits, the island’s 

hypersaline lake was deeper and had a 

coral bottom; devegetation by rabbits 

from 1903 to 1923 caused drifting sands 

to fill in the lake and some of the 

freshwater seeps on the island. A 

freshwater pond on the southwest side 

of the island was completely filled with 

sand (Ely and Clapp 1973). 

2. Lisianski Island 

Lisianski Island, approximately 250 

kilometers (155 miles) northwest of 

Laysan, is one-third Laysan’s size and 

has a similar geology and history 

(Figure 1). The island is about 11 

meters (36 feet) high at its highest point 

(Rauzon 2001). The presence of Laysan 

ducks on Lisianski was first noted by 

members of a Russian scientific 

expedition aboard the Moller in 1828, 

and the survivors of the shipwrecked 

Holden Borden in 1844 subsisted in 

large part by eating Laysan ducks 

(Olson and Ziegler 1995). The first 

visitors to the island noted an abundance 

of beach grasses and a few flowering 

shrubs, and fresh water was abundant, 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part I: Introduction and Overview. 

 8

though sometimes brackish (Polynesian 

1844 in Rauzon 2001). However, the 

ship sent to rescue the Holden Borden 

survivors in 1844 accidentally 

introduced an onslaught of mice, with 

devastating consequences for the 

vegetation on the island. Thirteen years 

later, a sea captain noted the nearabsence of plant life on Lisianski, save 

for a few coarse grasses and small vines, 

and the Laysan ducks that had formerly 

been present were not seen (Polynesian 

1857 in Rauzon 2001). What little 

vegetation the mice left behind rabbits 

soon depleted after they were introduced 

to Lisianski from Laysan around the 

turn of the century. By 1916 the rabbits 

on Lisianski had died out from 

starvation, and the lack of forage killed 

off the mice as well (Elschner 1925 in 

Rauzon 2001). Today the flora has 

mostly recovered and is similar to that 

of Laysan, with concentric zones of 

viney vegetation and bunch grass. The 

alien sandbur C. echinatus has become 

established, however, and is spreading 

in the native vegetation and along the 

coast (Starr and Martz 1999, Reynolds 

and Kozar 2000a). 

It is difficult to determine to what 

extent Lisianski’s invertebrate fauna has 

changed since human contact, but 

extensive alteration is likely. A recent 

survey listed 59 arthropod species on 

Lisianski, only 15 of which were 

indigenous to the island. The remaining 

species were adventive (unintentionally 

introduced, but able to colonize the 

island) and one was deliberately 

introduced (Nishida 1999). In addition, 

Reynolds and Kozar (2000a) found the 

native Agrotis moths and abundant 

larvae on Lisianski (both serve as prey 

for Laysan duck), which were not noted 

in Nishida’s 1999 species list. 

The interior of Lisianski once 

contained a wetland of fresh to brackish 

water, which sometimes was inundated 

with seawater during the highest tides 

(Polynesian 1844 in Rauzon 2001). 

Shifting sands destabilized by the loss of 

vegetation began to fill this wetland, and 

by 1857 nothing remained of it, though 

fresh water could be found by digging 

five feet below the surface (Polynesian 

1857 in Rauzon 2001). 

3. Prehistoric Habitat 

Recently acquired subfossil 

evidence reveals that Laysan ducks 

formerly occurred on most of the major 

Hawaiian Islands (Olson and Ziegler 

1995; Cooper et al. 1996; H. James, 

pers. comm. 2000; Figure 2). Remains 

of adult and flightless juvenile Laysan 

ducks have been found on Hawai`i 

Island at high elevations including sites 

on Mt. Hualalai (at 1,244, 1,792, 1,189, 

and 1,128 meters [4,080, 5,878, 3,900 

and 3,700 feet] above sea level), Mauna 

Kea, and Mauna Loa (1,524 meters 

[5,000 feet]). Remains from lower 

elevations (61 meters [200 feet]) were 

found near the coast at Hawai`i’s South 

Point. On Maui, remains were found at 

825 and 1,200 meters (2,706 and 3,936 

feet). On Moloka`i, subfossils were 

found at Mo`omomi dunes on the coast. 

Laysan duck bones were also found at 
9

Figure 2. Map of the Hawaiian Islands showing the Laysan duck’s known former range, current range, and site of unsuc

attempt in 1967. 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part I: Introduction and Overview. 

10

Kalaeloa (Barbers Point) on O`ahu, and 

on Kaua`i at Poipu, Makawehi, and 

Kealia dunes (H. James, pers. comm. 

2000). 

The Laysan duck’s prehistoric 

habitat on these high elevation islands 

was likely much different from that 

where the species is found today. The 

distribution of subfossils suggests that 

the species was a habitat generalist, 

inhabiting a range of environments from 

high elevation forests to coastal 

wetlands. Additionally, apart from an 

artificial lake on Kaua`i (created by 

Polynesian salt mining), no hypersaline 

systems exist in the main islands,

indicating Laysan ducks were not 

historically dependent on this type of 

habitat. 

D. General Biology and Ecology 

1. Habitat Use 

Prior to the discovery of bones in 

very diverse habitats on other islands, 

the Laysan duck was believed to be 

endemic to the Northwestern Hawaiian 

Islands, and particularly specialized for 

Laysan Island. Many factors have 

contributed to its current isolation, 

including introduced mammalian 

predators on the Main Hawaiian Islands 

and habitat loss due to introduced 

mammals on Lisianski combined with 

overexploitation by humans. The 

relevance of current habitat use is 

difficult to interpret when a species has 

declined to a single remnant population 

(Armstrong and McLean 1995). It is 

important to consider the possibility that 

some aspects of the ecological 

conditions on Laysan may not be ideal 

for this species. 

 

Habitat Use and Behavior on Laysan 

Island 

Laysan ducks are observed on all 

parts of the island but are typically 

hidden in the vegetation and difficult to 

observe during the day. Before sunset, 

the ducks emerge from the vegetation 

and are more visible, especially at the 

lake. Moulton and Weller (1984) found 

that the ducks were very active at night 

foraging at the lake. Warner (1963), 

however, described lake use as 

insignificant during the summer months 

of his study. There are four distinct 

habitat zones on Laysan Island that we 

have classified as camp, coastal, lake, 

and terrestrial (Figure 3). The camp 

zone occupies less than 1 percent of the 

island’s area, and is characterized by the 

presence of human structures, buckets, 

and tents. The coastal zone includes all 

habitats below the high surf line. The 

lake zone consists of the interior 

hypersaline lake, all wetlands, and 

mudflats. The terrestrial zone includes 

all “upland” vegetated habitats except 

those surrounding the camp. 

Radio telemetry and behavioral 

observations were used in 1998 through 

2000 to quantify habitat use in these 

four zones and the activity budgets of 

adult ducks on Laysan during three 

breeding seasons and one winter season 

(Reynolds 2002). Tracking data 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part I: Introduction and Overview. 

11

Figure 3. Map of habitat zones on Laysan Island.
Laysan Duck Draft Revised Recovery Plan, August 2004. Part I: Introduction and Overview. 

12

collected from 73 radio-tagged Laysan 

ducks during this time period indicate 

that individuals spend most of their time 

in the terrestrial habitats (59 percent). 

The lake zone was used 36 percent of 

the total time. Considerably less time 

was spent in the camp (4 percent) and 

coastal habitats (1 percent). Time 

budgets for activities within each habitat 

are given in Figure 4 (Reynolds 2002). 

Habitat selection analysis indicated 

that a few ducks selectively used the 

camp habitat and most avoided the 

coastal habitat except during the postbreeding period. Most of the birds 

showed strong evidence of selective 

habitat use by time of day (Reynolds 

2002), as detailed below. 

Daily Habitat Use and Behavior. 

In the morning, ducks were active and 

moved between habitats. During the 

middle of the day, ducks took cover 

under bunchgrasses (E. variabilis) or 

shrubs (S. sericea and Tournefortia 

argentea [tree heliotrope]). Most of the 

adult daytime activity budget was spent 

loafing or under cover in the terrestrial 

zone (76 percent). Very few birds (5 

percent of total telemetry locations) 

visited the lake habitat at midday, and 

their primary activity was foraging (44 

percent of time spent in foraging 

behavior). In contrast, duckling broods 

foraged both diurnally and nocturnally. 

At dusk birds moved actively between 

habitat zones. Some ducks visited 

coastal reef flats and coastal freshwater 

seeps in the late afternoon, and many 

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

CAMP COAST LAKE TERRESTRIAL

proportion time

undercover

active

forage

alert

loaf

Figure 4. Time activity budget of Laysan ducks in habitat zones of Laysan Island (n = 402 

observations; 8,511 minutes). 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part I: Introduction and Overview. 

13

birds visited the lake zone. The ducks 

rarely foraged on the coast. 

During the dusk session, ducks 

loafed (31 percent of the time), were 

active (28 percent), foraged (22 

percent), were alert (4 percent), or were 

under cover (10 percent) (Reynolds 

2002). Night tracking sessions showed 

that foraging was the most important 

activity (46 percent of time). 

Approximately 50 percent of the time 

spent at the lake at night was dedicated 

to foraging, and 41 percent of time spent 

in the terrestrial zone at night was spent 

foraging. Within the terrestrial zone, 

Laysan ducks selected the viney 

vegetation over the bunchgrass habitat at 

night. This viney vegetation association 

(Boerhavia-Ipomoea-Tribulus-Sicyos 

spp. [alena-pohuehue-nohu-anunu]) was 

a frequently used nocturnal foraging 

area, and had the highest invertebrate 

density and diversity of the terrestrial 

habitats. Night sessions lacked 

detections from the coastal zone, and 

few birds used the camp after dark 

(Reynolds 2002). 

Seasonal Habitat Use. During 

the breeding seasons of 1998 to 2000 

(typically April through July), the 

terrestrial zone was used more than the 

lake zone. Ducks spent less time at the 

lake during the 1998 breeding season

compared to the 1999 and 2000 

breeding seasons. Night tracking

indicated more time was spent in the 

terrestrial zone than the lake zone during 

the drought conditions of the 1998 

breeding season, compared with 

subsequent breeding seasons. This is 

perhaps explained by switching to 

terrestrial prey as a result of reduced 

prey abundance (brine flies) at the lake. 

Data from resighting color-banded 

individuals suggest that time spent in 

camp by some birds (“camp specialists”) 

increased from early spring to midsummer. Time spent in camp by radiotagged birds was correlated with an 

increase in moth abundance in camp 

(Reynolds 2002). 

 The coastal zone was rarely used 

during all months in which radio 

telemetry data were collected (less than 

1 percent of time spent there per month). 

However, a seasonal increase in the time 

spent in the coastal zone was evident 

from sightings. Flocks of up to 70 

Laysan ducks were recorded on the 

coast during the post-breeding season in 

September through February when radio 

tracking did not occur (Adams and 

Nevins 1994, McMahon et al. 1997, 

Reynolds 2002). The tidepools at the 

south end of Laysan were a principal 

flocking area following molt (September 

through November). Loafing, preening, 

fighting, courtship, copulation, and 

bathing were observed in the flocks 

using the coastal areas during this period 

(Reynolds 2002). 

Individual Variation in Habitat 

Use. Habitat use varied considerably 

among individuals. From 1998 through 

2000, 9 percent of the radio-tagged birds 

used the camp, 18 percent used the 

coastal zone, 96 percent used the lake 

zone, and all of the birds used the 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part I: Introduction and Overview. 

14

terrestrial zone (n = 53 birds). In the 

1999 and 2000 breeding seasons, some 

individuals rarely used the lake zone 

(Reynolds 2002). Moulton and Weller 

(1984) also found that some Laysan 

ducks did not use the lake.

Fresh Water. The freshwater seeps 

surrounding the lake are drinking areas 

for the ducks, Laysan finches (Telespiza 

cantans), and shorebirds. Seeps and 

other areas of relatively low salinity 

support greater algal growth and the 

accumulation of organic matter, which 

attracts higher numbers of brine flies. 

Laysan duck hens used ephemeral 

wetlands and freshwater seeps as brood 

rearing areas. Waterfowl have 

suborbital glands that function for salt 

removal (Schmidt-Nielsen and Kim 

1964) and adults drink saltwater; 

however, hypersaline (more than 3.3 

grams salt per 100 grams water) 

environments can be toxic to young 

ducklings with underdeveloped salt 

glands (Wobeser and Howard 1987). 

Although the adult Laysan duck has an 

efficient salt gland, the concentration of 

adults and ducklings at brackish seeps, 

freshwater seeps, and ephemeral 

freshwater wetlands implies these 

sources of low-salinity water are 

important (Lenz and Gagne 1986, 

Marshall 1989b, Moulton and Marshall 

1996). Antagonistic interactions 

between ducks and other bird species 

are frequently observed at the freshwater 

seeps. This contributes to duckling 

mortality from trauma (see Causes of 

Mortality). Fresh water may be a 

limiting factor for ducklings, especially 

during drought years, or if moisture-rich 

terrestrial invertebrates are scarce. 

Although freshwater seeps and 

ephemeral freshwater wetlands appear 

to be the primary source of fresh water, 

Laysan ducks can opportunistically take 

water from a variety of sources. Ducks 

drink dew and rainwater that has 

collected on vegetation, from pooled 

water on hardpan and mudflats after 

heavy rains, and from small excavations 

created around the lake to sample the 

water table. Around the camp, Laysan 

ducks readily drink water from buckets, 

camp structures, and watering devices. 

The ducks also obtain moisture from the 

ingestion of succulent plants such as 

Portulaca spp. (ihi) and terrestrial 

invertebrates (e.g., lepidopteran [moth 

and butterfly] and dipteran [fly] larvae). 

2. Foraging 

Food is a primary factor involved in 

regulating populations and influencing 

reproductive success of birds (Lack 

1970). The Laysan duck’s current 

foraging ecology on Laysan, like its 

habitat use, probably is quite different 

than its prehistoric foraging ecology on 

the main islands. Our understanding of 

the foraging ecology of this species on 

Laysan is growing. A better 

understanding of the range of food 

resources used on Laysan will help 

managers more accurately predict the 

suitability of potential release sites on 

other islands. 

 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part I: Introduction and Overview. 

15

There are many conflicting reports 

about the foraging ecology of the 

Laysan duck, possibly because of 

limited observations during short visits 

to the island and varying environmental 

conditions (Marshall 1989a). 

Introductions of alien species such as 

the snake-eyed skink (Cryptoblepharus

poecilopleuris), rabbits, ants, and other 

arthropods have had unknown impacts 

on the prey base and diet of the Laysan 

duck. We know that the native plant 

and arthropod communities of Laysan 

have been severely degraded in the last 

century (Conant and Rowland 1994, 

Morin and Conant 1998). Laysan ducks 

observed by Warner (1963) primarily 

fed terrestrially on moth larvae (Agrotis

dislocata), and these were an important 

component in the diet during 

observations from 1998 through 2000 

(Reynolds 2002). Warner considered 

the brine flies to be an incidental part of 

the diet and described the duck’s brine 

fly chasing behavior as infrequent. 

More recent data indicate that brine flies 

are an important component of their 

diet, at least seasonally (Caspers 1981, 

Moulton and Weller 1984, Reynolds 

2002). Warner (1963) reported a lack of 

fresh water during his study (conducted 

in the summers 1957 through 1961), so 

it is possible that brine fly abundance 

was low during Warner’s study periods 

or that drought conditions prevailed. It 

is also possible that native arthropods 

were more diverse and abundant in the 

past, prior to the introduction of alien 

predators such as ants, such that more 

terrestrial arthropods may have formerly 

been available as prey for the Laysan 

duck. Warner (1963) hypothesized that 

the shift in diet to greater reliance on 

brine flies was triggered by the 

introduction of a parasitic wasp (order 

Hymenoptera) that feeds on moth 

larvae, but no research has been carried 

out on the issue (Kear 1977). 

Diet Composition 

The Laysan duck is primarily 

insectivorous, but feeds 

opportunistically on seeds, leaves, and 

algae (Reynolds 2002). Behavioral 

observations indicate that adult and 

larval lepidopterans, adults and larval 

terrestrial dipterans, blatteria 

(cockroaches), grass seeds, sedge 

achenes, and succulent leaves are taken 

while foraging in terrestrial habitats 

(Reynolds 2002). Fecal samples were 

collected opportunistically from adult 

ducks in the summer of 1985 and in 

1998 through 2000. Analysis of fecal 

samples is a non-intrusive method for 

determining diet composition, but the 

method is biased towards finding 

insects, which have hard parts that are 

able to pass intact through the digestive 

system. Fecal samples contained items 

in 16 prey categories. Dipteran adults 

were the most common prey type 

identified and the most abundant prey 

item counted. Dipteran larvae, seeds, 

brine shrimp, lepidopteran larvae, 

beetles, and amphipods (sandhoppers) 

were also abundant in the samples, as 

were ants (Reynolds 2002; Table 1). 

Based on the birds’ behavior, and 

because so many specimens passed 

through the digestive system completely
Laysan Duck Draft Revised Recovery Plan, August 2004. Part I: Introduction and Overview. 

16

Table 1. Frequency of occurrence of taxa identified in Laysan duck fecal samples (proportions 

of samples with prey types) collected on Laysan Island at the lake in 1985 (Lenz and 

Gagne 1986) and 1998-2000 at both the lake and terrestrial habitats (Reynolds 2002).

Year n Prey type (Common name) 

Frequency of 

occurrence (%) 

1998-2000 118 Dipteran adult (adult flies) 47 

 Dipteran larvae/pupae (fly larvae or pupae) 39 

 Formicidae (ants) 36 

 Seeds 31 

 Lepidopteran larvae (butterfly or moth larvae) 25 

 Coleoptera (beetles) 23 

 Plant fibers 17 

 Artemia spp. (brine shrimp) 15 

 Acari (mites and ticks) 11 

 Amphipoda (sandhoppers) 8 

 Unknown arthropod 7 

 Dictyoptera (cockroaches and mantids) 3 

 Diptera terrestrial (terrestrial flies) 3 

 Lepidopteran adult (adult moth or butterfly) 3 

 Araneida (spiders) 2 

1985 28 Dipteran adult 

 (Neoscatella sexnotata) 

(brine fly) 39 

 Artemia (brine shrimp) 32 

 Lepidopteran larvae (moth or butterfly larvae) 32 

 Dictyoptera (cockroaches and mantids) 21 

 Dipteran larvae 

 (N. sexnotata) 

(brine fly) 21 

 Amphipoda (sandhoppers) 14 

 Dipteran terrestrial (terrestrial flies) 11 

 Acari (mites or ticks) 7 

 Araneida (spiders) 7 

 Formicidae (ants) 4 

 Dermaptera (earwigs) 4 

 Coleoptera (beetles) 0 

 Lepidopteran adult (moth or butterfly adults) 0 

 Plant fibers/Seeds 0 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part I: Introduction and Overview. 

17

undigested, ant consumption is likely 

incidental to the consumption of other 

prey. 

Foraging Behavior 

Laysan ducks utilized a variety of 

foraging behaviors and foraging 

substrates. Foraging behaviors in the 

lake include some tactics typical of 

dabbling ducks in aquatic environments: 

dabbling, up-ending, and head-dipping. 

Other more unusual foraging tactics 

included, ‘brine fly chasing,’ ‘dry sand 

filter feeding,’ and ‘dive-bomb’ flycatching. Unique foraging behaviors 

included tunneling through lake foam to 

feed on invertebrates suspended in the 

froth generated during high winds 

around the lake (M. Reynolds, pers. 

comm. 2002). At the lake zone, the 

ducks spent 6 percent of their total 

activity budget feeding on adult brine 

flies (Reynolds 2002). Brine fly 

foraging tactics included chasing after 

adult brine flies at a run, and snapping at 

flies while walking, standing, or 

swimming. Laysan ducks also took 

advantage of the carcasses of seabirds (a 

rich source of flies, larvae, and beetles), 

and the tents in camp, which trap moths 

(Warner 1963, Moulton and Weller 

1984, Moulton and Marshall 1996, 

Reynolds 2002). Historical records note 

that one duck used to forage near the 

house of the guano mining company’s 

director, looking for moths (Fisher 

1903). 

 Many duck species show notable 

shifts in diet during breeding. 

Generally, female dabbling ducks 

increase their consumption of proteinrich foods (animal matter) for egg 

production (Baldassarre and Bolen 

1994). The Laysan duck exhibited 

strong seasonal differences in brine fly 

foraging behavior. Between July and 

November 1998, no foraging on brine 

flies was observed, whereas from March 

to May 1999 (early in the breeding 

season) the ducks spent greater than 50 

percent of their foraging effort on brine 

flies, suggesting a preference for brine 

flies only when they are very abundant 

(more than 1,000 flies per unit area). 

Twenty-one percent of the total foraging 

effort at the lake before sunset was 

dedicated to feeding on brine flies 

during this early part of the breeding 

season (Reynolds 2002). 

Invertebrate Abundance 

The role of food availability in the 

population dynamics of dabbling ducks 

is not well understood (Owen and Black 

1990). The number of invertebrates in 

wetlands used for brood-rearing was a 

good predictor of mallard duckling 

growth and brood survival in other 

ecosystems (Cox et al. 1998). We 

suspect invertebrate abundance affects 

the female’s body condition and her 

ability to lay and incubate as well as 

duckling growth and survival on 

Laysan. Dramatic increases in brine fly 

densities can occur on Laysan, 

especially during wet La Niña years, and 

the ducks appeared to initiate successful 

breeding after these brine fly peaks in 

years when data were collected (U.S. 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part I: Introduction and Overview. 

18

Geological Survey [USGS] data 1998, 

1999; USFWS data 2000, 2003; see 

Figure 5). In contrast, there is evidence 

to suggest that during poor food years, 

such as the El Niño Southern Oscillation 

drought years, reproductive failure on 

Laysan is likely, perhaps owing to the 

low abundance of invertebrates in both 

the wetland and terrestrial habitats. 

Drought and reproductive failure 

occurred during El Niño Southern 

Oscillation events of 1987, 1993, and 

1998; low prey abundance was recorded 

in 1987 and 1998 (Marshall 1989b, 

Reynolds 2002). 

Lake Zone. A large number of 

insect species regularly inhabit areas 

adjacent to bodies of water and provide 

an important prey base for waterfowl. 

Most aquatic flies develop as aquatic 

larvae and pupae, emerging as adults 

that occupy the wetlands and margins of 

aquatic habitats. Changes in flooding 

regimes and lake depth are known to 

influence the abundance of aquatic 

dipterans. In particular, wetland 

flooding triggers the emergence of 

dipterans, and prolonged dry periods 

reduce fly emergence (McCafferty 

1998). 

Salt-tolerant aquatic organisms such 

as brine flies and brine shrimp can reach 

very high densities in hypersaline 

environments such as the lake on 

Laysan Island. Brine fly numbers and 

lake level were measured between 1998 

and 2000 to explore the relationship 

between water depth and fly emergence 

in this hypersaline ecosystem. Many 

factors ultimately are responsible for 

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

Mar-98

Apr-98

May-98

Jun-98

Jul-98Aug-98Sep-98Oct-98

Nov-98Dec-98Jan-99Feb-99

Mar-99

Apr-99

May-99

Jun-99

Jul-99

Aug-99

Sep-99

Oct-99

Nov-99

Dec-99

Jan-00Feb-00

Total mean brine flies per month

* 1ST DUCKLINGS * 1ST DUCKLINGS

Figure 5. Seasonal brine fly (Neoscatella sexnotata) abundance reported as monthly mean 

with standard error, and first brood sightings of Laysan ducks 1998 to 1999 

(Reynolds 2002).
Laysan Duck Draft Revised Recovery Plan, August 2004. Part I: Introduction and Overview. 

19

producing optimal conditions for the 

brine flies. Primary production, 

temperature, and nutrient loads are 

important ecological variables that 

influence the life cycle and abundance 

of wetland flies. Lake depth was a 

positive predictor of fly abundance 

because greater lake depths (as a result 

of increased rain and flooding) reduce 

salinity, which triggers fly emergence. 

There is, however, a time lag between 

flooding and fly emergence. Lake 

gauge measurements do not reflect the 

direct effect of water levels and salinity 

on mudflats, thus lake level and fly 

abundance are not synchronized 

(Reynolds and Kozar 2000a). 

 

Artemia, or brine shrimp, are 

zooplankton that inhabit high salinity 

ponds and lakes from which fish and 

most other crustaceans are excluded. 

On Laysan, the origin of the resident 

brine shrimp Artemia fransica has not 

been determined, but they are suspected 

to be an endemic race of the species 

(Lenz and Dana 1987). Artemia are 

abundant year-round and their 

distribution is influenced by prevailing 

winds (Reynolds and Kozar 2000a). 

Artemia are more salt-tolerant than brine 

flies and have a greater relative 

abundance at higher salinity. The 

primary predators on Artemia are 

waterbirds, but few waterbirds can 

subsist on Artemia alone. Red-necked 

phalaropes (Phalaropus lobatus) at 

Mono Lake in California, for example, 

exhibit a preference for brine flies and 

are unable to maintain their body weight 

when fed exclusively on Artemia 

(Rubega and Inouye 1994). Artemia

contain fewer calories and lipids (fats) 

than brine flies (Herbst 1986 in Rubega 

and Inouye 1994), which may explain 

why Laysan ducks prefer brine flies, a 

more nutritionally profitable prey when 

available at high densities. 

Terrestrial Zone. Comparisons of 

arthropod abundance in terrestrial 

vegetation types indicate that 

significantly more prey (dipterans, 

coleopterans [beetles], and adult and 

larval lepidopterans) occur in the viney 

and mixed vegetation complex 

compared with bunchgrass associations 

(see Habitat, above). One year of 

terrestrial arthropod sampling showed 

that arthropod abundance peaked in both 

vegetation types after the spring rainy 

period, however, longer term sampling 

is needed to determine seasonal trends 

or environmental conditions that 

influence “pulses” in terrestrial 

arthropod abundance (Reynolds 2002). 

Droughts are also likely to negatively 

impact terrestrial arthropod abundances. 

Camp Zone. Adult lepidopterans 

were the only arthropods sampled in the 

camp zone. There was a strong seasonal 

abundance pattern of moths in the years 

1999 through 2000, with abundance 

peaking during the summer months. 

There was a significant correlation 

(Pearson correlation coefficient = 0.84, 

p = 0.013) between the Laysan duck’s 

use of this habitat zone and prey 

abundance in 1999 (Reynolds 2002). 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part I: Introduction and Overview. 

20

3. Reproductive Biology 

Courtship Behavior 

Courtship behaviors occur most of 

the year on Laysan, and most adult pair 

bonds are established by September and 

October. Monogamous pairing and 

female-only parental care characterize 

the mating system of the Laysan duck. 

Pair bonds typically dissolve during 

brood rearing and molt (typically in 

summer), but if a brood fails early in the 

breeding season, females usually reunite 

with their original mates. Mate fidelity 

within a breeding year based on 

sightings data was 83 percent for 35 

known pairs. Over 2 years, 69 percent 

of mated pairs (n = 26 marked pairs) 

reunited once molt and brood rearing 

were complete (Reynolds 2002). 

Nesting 

Many ecological features affect 

waterfowl breeding, such as climate, 

hydroperiod, and temporal availability 

of suitable food (Baldassarre and Bolen 

1994), therefore the Laysan duck’s 

productivity is highly variable from year 

to year. The nesting season for the duck 

on Laysan generally runs from April 

through July, but reproductive response 

is flexible according to habitat 

conditions (Moulton and Marshall 

1996). Early broods were produced in 

December 1996 and 2000 (Bernard et al.

1996, Depkin and Lund 2001); abundant 

rainfall occurred during those years, and 

an abundance of prey was observed in 

2000 as well (Reynolds 2002). 

Compared to other dabbling ducks, 

Laysan ducks have a reduced clutch size 

(average 3.8 eggs) and very large eggs 

for their body size (Ripley 1960). Large 

eggs could be advantageous at hatching 

if bigger ducklings are better able to 

survive under less predictable feeding 

conditions typical of island ecosystems 

(Lack 1970). 

Laysan ducks should be considered 

“upland nesters,” because they typically 

choose nest sites far from the lake (mean 

distance 347.6 meters [1,140 feet) from 

lake and wetlands; range 15 to 850 

meters [49 to 2,789 feet]; n = 17 nests). 

Females tend to nest in their daytime 

home ranges (Moulton and Weller 1984, 

Reynolds 2002). Nests made from dead 

grass, rootlets, and down are well 

concealed under native bunchgrass and 

often hidden in grass clumps covered 

with vines (Sicyos spp.). Of the 26 total 

nests monitored, 92 percent occurred in 

the native E. variablis (Moulton and 

Weller 1984, Reynolds 2002). 

Incubation lasts 28 to 29 days 

(Marshall 1992a). Nest success (nests 

fledging at least one young) in 1999 and 

2000 averaged 44 percent (Reynolds 

2002), but previous studies reported 

much lower nest success (11 percent) 

due to egg predation by Laysan finches 

(Moulton and Weller 1984). Egg 

predation rates may have been elevated 

by human disturbance of nests. More 

recent studies, using methods modified 

to prevent nest disturbance by 

researchers, showed 13 percent of eggs 

scavenged or depredated by birds, 18 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part I: Introduction and Overview. 

21

percent infertile or undeveloped eggs, 

and 6.5 percent incomplete hatches. 

The fates of 8 percent of eggs were 

undetermined. Hatching success of 61 

eggs from 17 nests was 48 percent 

(Reynolds 2002). Our understanding of 

the nesting biology of the Laysan duck 

would benefit greatly from additional 

study. 

Brood Care 

Ducklings are precocial (hatched 

with down, open eyes, and the ability to 

forage) and leave the nest on the day of 

hatching (Marshall 1989b). Ducklings 

follow the hen very closely for the first 

4 days. During this period, hens lead 

ducklings from upland nesting sites to 

wetland brood rearing areas. Brood 

rearing areas are characterized by high 

densities of invertebrates, fresh or 

brackish water, and nearby vegetative 

cover (Cyperus laevigatus [makaloa] or

Ipomoea spp.; M. Reynolds, 

unpublished data). 

In years with high nesting success, 

the formation of creches (mixed broods 

from two or more hens) is common. In 

2000, 47 percent of hens with broods 

cared for ducklings that were not their 

own, and 32 percent of these hens 

appeared to raise broods cooperatively 

with other hens (n = 112 broods). 

Parental care such as guarding, 

brooding, leading, and following was 

combined or shared among two to four 

hens with ducklings of different age 

classes. At least 4 percent of hens 

observed had their ducklings taken by a 

more aggressive hen (Reynolds 2002). 

This level of brood mixing is 

unusual in dabbling ducks. The high 

rate of mixing might be explained by kin 

selection, female body condition, or 

improved foraging efficiency of larger 

broods (Eadie et al. 1988). Brooding 

females are often in poor nutritional 

condition by the time their young hatch. 

Female Laysan ducks with broods are 

the lightest of all adult birds, implying 

that maintaining normal weight during 

incubation is difficult (Moulton and 

Weller 1984). The energetic cost of 

brood rearing could reduce a hen’s 

chances of survival. If she relinquishes 

care of ducklings to a closely related 

female in good condition, both females 

might benefit: the mother increases her 

chances of survival, and the adoptive 

mother cares for closely related 

offspring that carry her genes. A form 

of reciprocal altruism could also account 

for the duck’s creching behavior, in that 

individuals caring for the young of 

others will likely be repaid in the future 

(Eadie et al. 1988). 

On Laysan, conditions might lend 

themselves to such a system: there is a 

high probability of meeting the same 

individual, there is strong site fidelity, 

birds are long-lived, and individual 

recognition probably is widespread. 

Furthermore, it is possible that larger 

broods forage more efficiently, and 

accepting the ducklings of another hen 

increases the fitness of a hen’s own 

ducklings. It is typical for 8 to 20 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part I: Introduction and Overview. 

22

ducklings of different age classes to 

form a foraging flock and run through 

swarms of brine flies (Reynolds 2002). 

As clouds of flies rise up from the 

disturbance, the ducklings snap at them 

while running with their necks 

outstretched (Moulton and Marshall 

1996). Alternatively, brood 

amalgamation may merely be a result of 

crowded brood rearing habitat and not a 

benefit to young or adults (Williams 

1974, Bedard and Munro 1977 in Batt 

et. al. 1992, Kehoe 1989). None of 

these possibilities has been investigated 

on Laysan. As not all hens adopt 

ducklings, creching behavior remains an 

enigma. 

Based on daily sightings of marked

hens with new ducklings at the lake (n = 

112 broods), 41 percent experienced 

complete brood loss during the downy 

duckling stage, and 23 percent of these 

ducklings died during their first week 

after hatching (Reynolds 2002). Seven 

percent of marked hens in 2000 

produced a second brood after losing the 

first one. Less than 25 percent of 

females reared broods to independence 

during the years 1977 to 1978 and 1986 

to 1987 (Moulton and Marshall 1996). 

In 1998 only 1 percent of color banded 

hens raised broods to independence, 

compared with 33 percent in 2000 

(Reynolds 2002). Complete 

reproductive failure occurred in 1987 

and 1993 (Marshall 1989a, Moulton and 

Marshall 1996). 

4. Demography 

Population Size 

Laysan duck populations have 

undergone severe fluctuations this 

century, with estimates from as few as 7 

adults in the early 1900’s to perhaps as 

many as 688 adult birds in 1961 

(USFWS 1982), although this high 

number is believed to be an 

overestimate (Marshall 1992b). Sincock 

and Kridler (1977) described the Laysan 

duck as the most difficult to survey of 

the four endangered birds of the 

Northwestern Hawaiian Islands. In the 

past decade alone, duck estimates have 

varied from fewer than 100 to 

approximately 600 individuals 

(Reynolds 2002). 

Previous researchers have 

determined that direct count and line 

transect methods are inadequate for 

determining population size in the 

Laysan duck (Sincock and Kridler 1977, 

Marshall 1992b). Mark-recapture and 

mark-resight methods yield the best 

results for this species (Moulton and 

Weller 1984, Marshall 1992b). Since 

1961, population estimates have been 

made using the Lincoln-Peterson index 

(Lancia et al. 1996), and field studies 

initiated in 1998 emphasized methods to 

more accurately determine population 

size. Since 1998, these estimates 

indicate that the population on Laysan 

Island has increased from 288 to 459 

adult birds as of 2001 (Table 2; 

Reynolds 2002). For a more detailed 

discussion of current monitoring
Laysan Duck Draft Revised Recovery Plan, August 2004. Part I: Introduction and Overview. 

23

Table 2. Estimates of Laysan duck population size on the island of Laysan using line-transect 

and mark-resight methods. 

Year 

Estimated 

number of 

adults 

95 % 

confidence 

interval Method used Notes 

Number 

of birds 

marked Source 

1958 594 None 

published 

Line transect n/a Warner 1963 

1961 688 None 

published 

Line transect n/a Warner 1963 

1961 544 404 - 831 Lincoln- Petersen 

Index 

Estimates 

recalculated in 2001 

149 R. Walker, 

unpublished 

field notes 

1979 489 432 - 540 Lincoln- Petersen 

Index 

April estimate 269-296 Moulton and 

Weller 1984 

1980 510 None 

published 

Lincoln- Petersen 

Index 

 502 Moulton and 

Weller 1984 

1986 423 ± 128 SE Lincoln- Petersen 

Index 

Mean estimate 

Jun-Aug 

200 Marshall 

1992b 

1987 538 ± 73 SE Lincoln- Petersen 

Index 

Mean estimate 

April-June 

270 Marshall 

1992b 

1998 288 232 -434 Lincoln- Petersen 

Index 

Adult estimate 100 Reynolds 2002 

1999 292 263 - 321 Lincoln- Petersen 

Index 

Adult estimate 158 Reynolds 2002 

2000 322 290 - 354 Lincoln- Petersen 

Index 

Adult estimate 220 Reynolds 2002 

2001 459 391 - 537 Lincoln- Petersen 

Index 

Adult estimate 260 Reynolds 2002 

methods, see Laysan Duck Population 

Monitoring, below. 

Sex Ratio 

The sex ratio of Laysan ducks on 

Laysan Island typically is skewed 

toward males. Male to female ratios in 

1979 and 1980 were reported as 56:44 

by Moulton and Weller (1984), who 

noted female mortality from attacks by 

unpaired males. Harassment and forced 

copulation of females by unmated males 

occur occasionally, but may increase in 

frequency with the number of extra 

males in the population. Recent sex 

ratios were less skewed. The estimated 

sex ratio was even in 1998, 53:47 in 

1999, 52:48 in 2000, and even in 2001 

(Reynolds 2002). No adult female 

mortality resulting from trauma was 

observed from 1998 through 2001, when 

the ratio of males to females was lower. 

Mortality and Survival 

From 1998 through 2000, the annual 

survival rate for adult males was 

estimated at 98.1 percent, and the 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part I: Introduction and Overview. 

24

estimate for adult females was 97.8 

percent. Duckling survival varied from 

approximately 10 to 30 percent during 

this same time period (Reynolds 2002). 

This level of duckling survival is 

considered poor for a waterfowl 

population lacking mammalian 

predators. On Laysan the great 

frigatebird (Fregata minor) is the only 

potential resident predator on ducklings. 

Frigatebirds have been observed to take 

the chicks of terns and other seabirds 

(A. Marshall, pers. comm. 2002), but 

because frigatebirds have never been 

observed to take ducklings, the total 

impact of great frigatebird predation on 

ducklings is presumed to be minimal. 

The ducks are alert to great frigatebirds 

and ducklings have been observed 

diving underwater when frigatebirds 

descend or swoop down near them. 

Duckling survival is an important 

variable controlling population growth 

on Laysan (Warner 1963, Reynolds 

2002)

 Causes of Mortality. Laysan duck 

carcasses are rarely found, and few 

causes of adult or duckling mortality 

have been identified, with the exception 

of the 1993 die-off caused by starvation 

and echinuriasis (see Diseases, below). 

Data from carcasses incidentally 

collected in 1993 and 1998 through 

2001 revealed that factors contributing 

to mortality were quite different for 

adults and juveniles. Of the 86

carcasses found, 45 were suitable for

exam and cause of death could be 

determined definitively in 33 cases; the 

remaining 12 cases represent educated 

guesses. Most adult mortalities were 

caused by starvation and infestation by 

the nematode Echinurea uncinata

(echinuriasis) (n = 14). An adult female 

was found egg-bound and also suffering 

echinuriasis. Two adults were found 

dead from starvation (no sign of 

nematodes), and one adult died of 

bacterial encephalitis (National Wildlife 

Health Research Center [NWHRC] 

1993, 1998, 1999, 2000, 2001). 

Moulton and Weller (1984) reported 

adult mortality by sexual attack and 

seabird collision during studies in 1978 

and 1979, but no adult carcasses from 

1993 or 1998 through 2001 exhibited 

any signs of trauma. In the summer of 

2003, the first case of (adult) mortality 

due to avian botulism was documented 

(T. Work, pers. comm. 2003). 

Most ducklings, in contrast, died of 

traumatic injuries (n = 27). Aggression 

has been observed toward ducklings by 

non-reproductive adult ducks, and 

rarely, by hens with broods toward a 

duckling from another brood. Stray 

ducklings are often bitten or charged if 

they approach a non-parent (M. 

Reynolds, pers. obs.). One such attack 

was suspected to cause duckling 

mortality (Boswell and Keitt 1995). 

Attacks on ducklings by adult ducks 

have been reported in other species in 

crowded habitats where food may be 

limited (Pienkowski and Evans 1982 in 

Johnson et al. 1992). Ducklings are also 

susceptible to trauma from aggression 

by albatross and other large seabirds, 

which are abundant on Laysan. In 1992 

our field staff found 10 ducklings with 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part I: Introduction and Overview. 

25

crushed skulls. Great frigatebird attacks 

were suspected as the cause of death 

(Newton and Chapelle 1992). 

Of the 27 duckling carcasses 

suitable for exam, 7 exhibited no 

obvious signs of trauma, starvation, or 

disease; these deaths were attributed to 

exposure to adverse weather. Duckling 

mortality has been ascribed to exposure 

of ducklings separated from the brood, 

especially during rainstorms (Moulton 

and Marshall 1996). Few ducklings 

died of echinuriasis, pneumonia, or 

starvation. Seven of 13 downy-stage 

duckling carcasses examined contained 

yolk sac remains, indicating these birds 

did not die of starvation (NWHRC 1998, 

1999, 2000, 2001; Figure 6).

Mortality trends. Brood 

monitoring data and the age structure of 

incidental carcasses found between 1998 

and 2000 (n = 86) reveal that the 

downy-stage ducklings are the most 

vulnerable, especially during the first 6 

days after hatching. Most carcasses (76 

percent) found were ducklings in the 

downy plumage stages less than 18 days 

old (Figure 7). Duckling carcasses from 

1998 through 2001 were found mostly 

in the spring and summer after the peak 

of hatching (Reynolds 2002). Of the 

carcasses recovered in 1998 through 

2000, adults comprised 16 percent of the 

specimens, 57 percent of which were 

females. Most adult carcasses from 

those years were found in mid- to late 

summer after the peak of breeding. 

Adult carcasses during the 1993 die-off 

were found from August 1993 to 

January 1994 (Darnall and White 1993, 

Bauer and Gauger 1994). 

5. Population and Species 

Viability 

Delisting through elimination or 

reduction of threats and population 

restoration is the recovery goal for the 

Laysan duck. To reach this goal, it is 

necessary to achieve viability for the 

duck. A viable species is one that will 

persist over a long period of time (by 

convention, more than100 years) and 

that exhibits resilience in an 

environment subject to random, 

naturally occurring (stochastic) 

disturbances. Viability may be attained 

by maintaining independent viable 

populations or by having multiple 

interconnected populations; in the latter 

case, none of these populations is 

necessarily viable by itself, but 

collectively the constituent populations 

function as a larger interdependent 

“metapopulation” (Levins 1968). In an 

analysis of Hawai`i’s historic avian 

extinctions, the pattern is that species 

having large, well-distributed 

populations are most likely to persist 

over time (Hu 1998). A population that 

becomes sufficiently reduced in size 

becomes vulnerable to stochastic forces, 

which often lead to its extinction (Meffe 

and Carroll 1997). 

Population persistence models were 

employed to forecast possible 

population fates for the Laysan duck 

resulting from the effects of a variety of 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part I: Introduction and Overview. 

26

 

0

2

4

6

8

10

12

14

16

STARVATION

EMACIATION+ECHINURISIS

ECHINURISIS

TRAUMA

BACTERIAL INFECTION

SUSPECT EXPOSURE

EGG BOUND

Number carcasse

s

Ducklings

Adults

I b duckling 7-12 days

I c duckling 13-18 days

II a duckling 19-25 days

II b duckling 26-35 days

II c duckling 36-45 days

III a duckling 46-60 days

III b duckling 52-63 days

III c duckling 63-73 days

Adult (after hatch year)

I a duckling 1-6 days

Figure 6. Causes of mortality for Laysan duck adults and ducklings found dead 1993 

to 2001 (n = 45).

Figure 7. Laysan duck carcass age class breakdown from 1998 to 2001 (n = 86). 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part I: Introduction and Overview. 

27

scenarios. These models, called 

population viability analyses (often 

abbreviated as PVA), are widely used to 

evaluate extinction risk and to assess 

management options for species 

recovery. Factors included in the 

simulation included demographic, 

environmental, catastrophic, and genetic 

threats. Information on the Laysan 

duck’s birth and survival rates, 

population size, estimated habitat 

capacities of different islands, and the 

frequency of threats were put into the 

program VORTEX (Version 8.41; Lacy 

1993) and projected forward in time. 

Information entered into the population 

viability model was based on population 

data from Laysan, published life history 

characteristics, and best estimates for 

other parameters (the parameters used 

are provided in Appendix 3). Some 

variables, such as the rate of population 

growth and the carrying capacity of 

potential translocation sites, were 

estimated based on data collected on 

Laysan; these conditions (or population 

parameters) may vary considerably from 

island to island. We assumed no 

inbreeding depression in the population 

on Laysan, but this may not be realistic. 

Real values of genetic heterozygosity (a 

measure of genetic variability) should be 

considered in future models once 

genetic data are available. These were 

the weakest components of the model. 

Data collected from a well-monitored 

experimental translocation flock will 

improve demographic, genetic, and 

carrying capacity estimates needed to 

improve estimates of population 

persistence. 

The simulation was run 100 times 

for a 100-year time period and forecast a 

low (57 percent) chance of long-term 

persistence for the Laysan duck 

population under current conditions. Of 

these 100 simulations, the Laysan duck 

went extinct on Laysan 43 times, with a 

mean time-to-extinction of 38.7 years. 

The viability of the species was also 

simulated under possible scenarios that 

included additional populations on other 

Northwestern and Main Hawaiian 

Islands. Each additional population 

improved the potential for the species’ 

persistence. Five populations 

representing a combination of sites on 

the Northwestern and Main Hawaiian 

Islands and a mean final population size 

of 611 (± 308 SD) birds yielded the 

greatest probability (99 percent) of 

Laysan ducks persisting for 100 years. 

Longer time projections were not 

considered in these exercises, as shorter 

time projections minimize the 

propagation of errors in such models 

and allow for evaluation of conservative 

extinction probabilities (Beissinger and 

Westphal 1998). The detailed results of 

the population viability analyses 

modeled for the Laysan duck are 

summarized in Appendix 3. 

The entire species of the Laysan 

duck is now limited to one small 

population on an island with limited 

carrying capacity, and the risks to that 

population are considerable. In addition 

to protection of the Laysan population, 

an appropriate management strategy to 

attain long-term viability for the Laysan 

duck includes restoration and 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part I: Introduction and Overview. 

28

management of habitat, removal of 

introduced predators in suitable habitats 

in the Main Hawaiian Islands, and the 

establishment of additional wild 

populations that are managed to 

maintain genetic variability. 

As a first step, an aviary-held or semicaptive (supplemented) Laysan duck 

population should be established at one 

or more suitable sites on other islands 

while habitat restoration proceeds. 

Ideally restored habitats are expected to 

support wild populations that do not 

require intensive management; however, 

intensive management will be required 

in some areas. 

Threats to Population Viability 

Extinction can be considered a twophase process. Primary factors can 

cause initial population reductions at 

broad spatial scales (Hu 1998). After 

populations have declined, secondary 

threats are likely to affect the species, 

because of its reduced population size 

and possibly restricted distribution. 

Island species are especially vulnerable 

to anthropogenic extinction because of 

their particular adaptations, such as 

reduced reproductive rates, ecological 

naïvete (i.e., unfamiliarity with 

mammalian predators), and low 

resistance to new diseases (Temple 

1985). 

Primary threats. The broad causes 

for bird extinctions have been classified 

into four main categories: 1) harmful 

species introductions, 2) human 

exploitation, 3) habitat loss, and 4) 

trophic cascades (secondary extinctions) 

(Diamond 1984a in Hu 1998). The 

extirpation of Laysan ducks from the 

Main Hawaiian Islands is estimated to 

have occurred about 1,500 years ago. 

Harmful species introductions, human 

exploitation, and habitat loss are 

suspected as the primary factors 

responsible for their decline. The 

disappearance of the Laysan duck is 

coincident with the appearance of rats in 

Hawai`i’s chronological subfossil record 

(Burney et al. 2001). The devastating 

effect of introduced rats on groundnesting Hawaiian birds is well 

documented (Berger 1981). Evidence 

indicates that Polynesian rats (Rattus 

exulans) were more widely distributed 

than humans during the period of early 

human colonization, suggesting that rats 

were a primary cause for the duck’s 

extirpation (Burney et al. 2001). This 

threat is still present on most of the 

Main Hawaiian Islands, and additional 

predators have been introduced since 

Western colonization, including black 

rats (R. rattus), Norway rats (R. 

norvegicus), house cats (Felis cattus), 

dogs, pigs, and Indian mongooses 

(Herpestes auropunctatus; Scott et al.

1986). 

Secondary Threats. A population 

that is sufficiently reduced or isolated 

becomes increasingly vulnerable to 

secondary threats, and these must be 

adequately addressed to ensure species 

viability. These are primarily stochastic 

threats (the result of chance events), and 

when they act on a small, localized 

population, such threats can lead to 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part I: Introduction and Overview. 

29

extirpation or even extinction. Laysan 

ducks are highly vulnerable to 

demographic and environmental 

stochasticity, and may be vulnerable to 

genetic drift and inbreeding (genetic 

stochasticity, Shaffer 1981; see Genetic 

Considerations, below). Demographic 

stochasticity is the effect of random 

events on the reproduction and survival 

of individuals, and is usually considered 

to be a threat only to small populations 

(Meffe and Carroll 1997). In the case of 

the Laysan duck, such a chance event 

might include an uneven sex ratio that 

leads to increased female mortality from 

harassment by excess males in the 

population. Environmental stochasticity 

refers to unpredictable variation in 

climate or other parameters that affect 

vital rates of an entire population (as 

opposed to individuals), such as drought 

during the breeding season that affects 

food supply, or heavy rain that floods 

nests during incubation. The effects of 

environmental stochasticity are similar 

whether the population is large or small 

(Caughley 1994). 

Extremes of environmental 

stochasticity, such as severe storms, 

droughts, and tsunamis, and of 

anthropogenic disturbance, such as an 

introduction of rats to Laysan or sea 

level rise resulting from global 

warming, may be catastrophic for the 

Laysan duck under current 

circumstances. Disease and other 

anthropogenic threats also pose serious 

risks (see Current Threats, below). The 

impact of these threats can be reduced 

by: 1) having many populations 

geographically spaced to decrease the 

chance of a catastrophe simultaneously 

affecting all populations; 2) 

reestablishing birds on larger islands, for 

example, Kaua`i and Kaho`olawe, that 

provide more protection from storms 

and sea level changes; and 3) 

developing post-disaster contingency 

plans to restore populations affected by 

catastrophes. 

Genetic Considerations. The 

viability of isolated populations may be 

threatened by genetic stochasticity, 

especially if the population is small. 

Decreasing population size eventually 

leads to inbreeding, and possibly to 

inbreeding depression (the reduction of 

reproductive fitness and vigor through 

breeding with close relatives). The 

effects of genetic drift (changes in allele 

frequencies through chance fluctuations, 

rather than selection [an allele is an 

alternative form of a gene]) is also 

amplified in small populations. Random 

mutation produces deleterious alleles in 

any population, but such changes may 

spread rapidly through a small 

population (Caughley 1994). These 

genetic effects may increase the 

vulnerability of a species to extinction 

by reducing the genetic variability 

required to adapt in response to new 

selective pressures. 

 

The Laysan duck may have suffered 

an initial genetic bottleneck after the 

species first became isolated on Laysan, 

and very likely suffered another when 

the population fell to only 12 individuals 

(7 adults and 5 juveniles) in 1912 during 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part I: Introduction and Overview. 

30

the rabbit infestation of the island (Dill 

and Bryan 1912). As a result, the 

species is likely to have a low level of 

genetic variability. The reduction in 

fitness from inbreeding depression is 

often expressed as low reproductive 

success, reduced hatchability, and lower 

disease resistance (Friend and Thomas 

1990). We have no indication that 

Laysan ducks exhibit these signs, but a 

comprehensive study of their breeding 

biology on Laysan has never been 

conducted, and nothing is known of 

their disease resistance. Genetic 

samples were collected from 

approximately 200 wild individuals in 

the years 1998 through 2000; analysis of 

these samples is needed. Individuals or 

their offspring with high levels of 

genetic variability would be desirable as 

founders, immigrants, and for captive 

breeding stock. 

The susceptibility of island 

populations to the negative effects of 

inbreeding is uncertain, and the 

conservation genetics of the Laysan 

duck have not been studied. It is 

possible that many deleterious alleles 

have already been purged over time and 

reduced genetic variation will not 

manifest itself as inbreeding depression 

in this remnant population. However, 

preliminary results from studies of 

individual genetic variation and disease 

resistance in Hawaiian honeycreepers 

suggest that birds with greater genetic 

variation demonstrate higher resistance 

to an introduced disease, avian malaria 

(S. Jarvi et al. in prep.). Furthermore, 

genetic variation is the basis for 

evolutionary potential, and the ability of 

a species to persist over the long-term is 

closely tied to the reservoir of genetic 

diversity upon which it may draw to 

successfully respond to environmental 

change (Fisher 1930, Allendorf and 

Leary 1986). 

E. Reasons for Decline and 

Current Threats 

The Laysan duck was included in 

the original Endangered Species List of 

1967 because of its small population 

size, limited distribution, and 

dependence on a fragile island 

ecosystem (USFWS 1967). The threats 

to the species and its habitat today are 

the same as in 1967, when the Laysan 

duck was listed, and in 1982 when the 

original recovery plan was published 

(USFWS 1982). Until 1995 the species 

was believed to be endemic to the 

Northwestern Hawaiian Islands, but we 

now have new information on the wider 

historical and prehistorical distribution 

of the species in Hawai`i. Recent 

discoveries of Laysan duck subfossils on 

other islands provide justification for 

reestablishment of the species in 

portions of its former range as a critical 

component of recovery (Cooper et al.

1996). 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part I: Introduction and Overview. 

31

1. History of Decline: Range 

Contraction and Reduced 

Numbers 

Northwestern Hawaiian Islands 

The range of the Laysan duck within 

historical times has been limited to the 

islands of Lisianski and Laysan. The 

shipwrecked castaways on Lisianski and 

visitors to Laysan Island ate Laysan 

ducks. Reports describe the naïve birds 

as “tame,” which certainly facilitated 

their exploitation (Polynesian 1844 in 

Rauzon 2001, Olson and Ziegler 1995). 

The population on Lisianski likely 

disappeared after successive shipwrecks 

between 1844 and 1846. Introduced 

mice probably accelerated their decline 

by competing for food and destroying 

vegetative cover (Olson and Ziegler 

1995). Today the species is found only 

on Laysan Island. 

Since their restriction to Laysan 

Island, the ducks probably have never 

been very numerous. In 1891 a visitor 

to the island described the bird as “not 

very plentiful” (Rothschild 1893-1900), 

and 11 years later Walter Fisher wrote 

“the Laysan duck is, of all the birds on 

the island, the one most likely to be 

exterminated when the present favorable 

regime comes to an end. There are 

probably less than a hundred of this 

species now living.” (Fisher 1903). 

Indeed, the Laysan duck came to the 

brink of global extinction in 1911 during 

a period of commercial guano mining by 

the Northern Pacific Phosphate and 

Fertilizer Company (Ely and Clapp 

1973). Rabbits were introduced to 

Laysan and Lisianski Islands around 

1903. The rabbits overpopulated and 

devegetated both islands. The duck 

underwent a severe population 

bottleneck during this period: only 

seven adults and five juveniles were 

observed in 1912 (Dill and Bryan 1912). 

Through a combination of starvation and 

deliberate eradication, rabbits were 

eliminated by 1923, and shortly 

thereafter both the vegetation and the 

duck population began to recover. By 

1957 the population had climbed to 

around 500 birds, which seems to be 

about the present carrying capacity of 

the island (Moulton and Weller 1984, 

Moulton and Marshall 1996). 

Prehistoric distribution 

The Hawaiian Islands are the most 

isolated archipelago in the Pacific, with 

a unique faunal history and late 

colonization by humans (1,400 to 1,600 

years before the present; Kirch 1982). 

Anthropogenic predation and habitat 

change since human settlement have had 

severe impacts on native birds of islands 

(Cooper et al. 1996), and Hawai`i 

provides graphic examples of humancaused extinction and extirpation events. 

Waterfowl were conspicuous casualties 

of human impact on indigenous fauna 

(Williams 1996). Subfossils represent at 

least eight species of extinct Hawaiian 

waterfowl, the largest unique 

assemblage of waterfowl known. 

Hawai`i’s extinct waterfowl include the 

moa-nalo, large flightless herbivorous 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part I: Introduction and Overview. 

32

duck species, and a large flightless 

goose (Olson and James 1991). Only 

three species of endemic waterfowl 

remain in the islands, and all three have 

been listed as endangered since the first 

list of endangered species was published 

in 1967: the nēnē (Branta sandvicensis), 

the koloa, and the Laysan duck (USFWS 

1967). Subfossil evidence has recently 

revealed that Laysan ducks formerly 

occurred on most of the major Hawaiian 

Islands, including Hawai`i, Maui, 

Moloka`i, O`ahu, and Kaua`i (Olson and 

Ziegler 1995, Cooper et al .1996, H. 

James, pers. comm. 2000; see Figure 2). 

2. Current Threats 

The small number of Laysan ducks 

in the single remaining population and 

their highly restricted geographic range 

on an island with limited carrying 

capacity is the greatest ultimate threat to 

this species. The Laysan Island duck 

population experiences periodic crashes 

due to chance events, and given the 

small size of the population, such events 

pose a significant threat to its existence. 

The most recent population crash was in 

1993, when the island suffered a severe 

drought. Laysan Island is vulnerable to 

severe storms, and global warming 

could increase the frequency and 

intensity of storms. Alien plant and 

insect species continue to invade the 

island, and the likelihood of additional 

introductions is high, as is the chance of 

oil spills or other contaminants washing 

ashore. Parasite outbreaks have 

occurred, and other diseases are a 

potential problem that remains 

unassessed. All of these factors pose 

particularly grave risks to the Laysan 

duck as the risks posed by stochastic 

events increase as population size 

decreases. Any of the threats described 

below has the potential to cause the 

extinction of the Laysan duck (see 

Population and Species Viability, above; 

Mangel and Tier 1994, Townsend et al.

2000). 

 The threats to the Laysan duck are 

each classified according to the five 

factors identified under section 4(a)(1) 

of the Endangered Species Act in 

consideration for listing, delisting, and 

reclassification decisions. These five 

factors are as follows: 

A – Present or threatened destruction, 

modification, or curtailment of 

habitat or range; 

B – Overutilization for commercial, 

recreational, scientific, or 

educational purposes; 

C – Disease or predation; 

D – Inadequacy of existing regulatory 

mechanisms; and 

E – Other natural or man-made factors 

affecting the continued existence of 

a species. 

Anthropogenic Threats 

Alien Species (Factors A and C). 

Nonnative plants, invertebrates, and 

vertebrates all pose indirect threats to 

the Laysan duck (Factor A). Introduced 

plants displace native vegetation, 

destroying preferred nesting habitat and 

cover for birds, and may reduce foraging 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part I: Introduction and Overview. 

33

habitat for native arthropods. At least 

150 nonnative invertebrates have found 

their way to Laysan (Morin and Conant 

1998, Nishida 1999). The role of 

introduced predatory arthropods and 

their competition for terrestrial prey has 

not been studied on Laysan. Ants, 

which are not native to Hawaiian 

ecosystems, are extremely destructive to 

native species. Researchers believe bigheaded ants (Pheidole megacephala) 

caused mortality of nestling Laysan 

finches (Conant and Rowland 1994). 

An introduced vertebrate, the snakeeyed skink, could also be a food 

competitor and may adversely affect 

native invertebrates (Morin and Conant 

1998). 

Future accidental introductions also 

pose a serious risk. Other islands in the 

northwestern Hawaiian chain have 

experienced recent invasions of exotic 

plants, ants, grasshoppers, mosquitoes, 

spiders, reptiles, mice, and rats, any of 

which could have severe impacts on the 

native flora and fauna of Laysan 

(Conant and Rowland 1994, Morin and 

Conant 1998). Quarantine measures are 

in place, but even if strictly enforced, 

uncontrollable events could result in the 

introduction of new species to the 

island. In 1970, for example, a Japanese 

fishing vessel ran aground on Laysan’s 

south shore. An investigation of the 

ship found evidence of rats aboard, 

though none were ever discovered on 

the island (USFWS 1982). Three boats 

have wrecked off Kure Atoll in the past 

5 years. In 2000, 10 new species of 

introduced arthropods (14.3 percent of 

total species collected) were identified 

on Laysan from prey samples collected 

during Laysan duck prey monitoring 

from 1998 through 2000 (Nishida 2000, 

Reynolds 2002). 

Although not currently a problem on 

Laysan Island, the introduced 

mammalian predators that were in large 

part accountable for the extirpation of 

the Laysan duck throughout most of its 

former range still pose the greatest 

direct threat to the recovery of the 

species (Factor C). Recovery of the 

Laysan duck will require 

reestablishment of the species on at least 

some of the Main Hawaiian Islands, 

nearly all of which are inhabited by 

numerous alien predators, including 

cats, dogs, pigs, mongooses, and several 

species of rats. Such alien predators 

have devastating effects on groundnesting birds (Berger 1981, Scott et al. 

1986, Burney et al. 2001), and adult 

ducks are vulnerable to predation as 

well. Laysan ducks are incapable of 

flight during their annual molt, and they 

also tend to run or freeze in place rather 

than fly as an escape response, having 

evolved in the absence of terrestrial 

predators. 

Filling of lake and seeps (Factor 

A). The interior lake and surrounding 

freshwater seeps have undergone 

sedimentation exacerbated by the rabbitcaused devegetation and shifting 

shorelines (Bailey 1919, Wetmore 1925 

in Ely and Clapp 1973). Open, 

devegetated spaces, called “blow-outs,” 

persist on the island today. Small sand 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part I: Introduction and Overview. 

34

storms develop during windy weather, 

sometimes forming short dunes that drift 

into seeps and ponds (Morin and Conant 

1998). Drifting sands have caused the 

lake to shrink since the turn of the 

century. Maximum lake depth was 

reported as 9.1 meters in 1859, when the 

lake had a coral bottom. By 1923 the 

lake depth was 4.6 meters with a sand 

bottom, though the depth tends to vary 

seasonally and with rainfall: in 1986 the 

maximum depth was 6.5 meters (Ely 

and Clapp 1973, Lenz and Gagne 1986). 

Reports described a permanent 

freshwater pond on the southwest 

interior of Laysan until 1923, when it 

was completely filled by sand. Early 

visitors to the island noted ducks 

concentrating in and around the pond 

(Ely and Clapp 1973). Recent 

observations show that ducks spend a lot 

of time foraging at the lake in areas with 

lower salinity and at freshwater seeps, 

which have the highest prey densities 

and are an important source of fresh 

water for ducklings (see Habitat Use, 

above). Lower salinity favors the 

growth and emergence of brine flies, an 

important prey source for the ducks. 

Contaminants (Factor E). Pacific 

Ocean currents often carry debris to 

Laysan’s shores. In 1988 a 

contaminated site (the “dead zone”) was 

discovered on the island’s northern 

coast. Dead insects, crabs, and birds 

were recorded within the zone’s 

perimeter (Morin and Conant 1998), 

including one Laysan duck in 1987 (B. 

Becker, pers. comm. 2002). A container 

of the pesticide carbofuran was 

identified as the cause. The 

contaminated substrate was excavated 

and removed from the island in 2002 (L. 

Woodward, pers. comm. 2002).

 

Oil from spills has also washed up 

on the island. The most recent known 

spill was in the winter of 2000, when 

numerous tar balls were seen on the 

west coast. That winter eight oiled birds 

were found on the island: seven Laysan 

albatross (Phoebastria immutabilis) and 

one red-footed booby (Sula sula 

rubripes) (Eggleston and Gellerman 

2000). Although no Laysan ducks were 

known to be affected by that spill, an 

oiled Laysan duck was seen in 1999 (M. 

Berry, pers. comm. 1999). Future 

contaminants washing ashore could pose 

a serious threat to the Laysan duck 

population. Even small amounts of 

contaminants can affect vital rates 

through decreased egg production, 

reduced fertility and hatchability, and 

lower sperm counts (USFWS 1987). 

Global warming and sea level 

rise (Factor E). Because Laysan is 

such a low island (12 meters [39 feet] at 

its highest point) it is especially 

vulnerable to a rise in sea level. 

Atmospheric temperatures are expected 

to increase between 1.4 and 5.8 degrees 

Celsius (2.5 and 10.4 degrees 

Fahrenheit) in the next century, with a 

concomitant rise in sea levels of 21 

centimeters (8.3 inches) by the year 

2050 (IPCC [International Panel on 

Climate Change] 2001). Even a slight 

rise in sea levels would destroy a large 

portion of the duck’s current habitat 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part I: Introduction and Overview. 

35

through increased flooding of the 

terrestrial upland habitats and increased 

salinity of the groundwater supply. 

Another anticipated effect of global 

warming is increased frequency and 

severity of storms (IPCC 2001) (see 

Storms, below). 

Field camp (Factor E). A 

permanent field camp is set up on the 

northwest coast of the island. Staff must 

be cautious in their use of pesticides and 

monitor the possible effects of a new 

well on the island’s aquifer. Hens that 

nest in E. variabilis near camp may lead 

ducklings into camp; therefore, staff 

should take care not to disturb or 

fragment broods. 

Diseases 

Viruses, bacteria, and invertebrate 

and fungal parasites can all affect bird 

populations. Depending on its severity, 

a disease outbreak can be considered a 

natural catastrophe. Waterfowl 

populations in particular are susceptible 

to epizootics, in part because these birds 

are often gregarious or concentrated in a 

few refuges, thereby facilitating disease 

transmission (Baldassarre and Bolen 

1994). Laysan ducks are known to 

experience mortality from infection by a 

parasitic nematode, but the threat of 

other diseases is currently unevaluated. 

Most diseases require a certain 

proportion of susceptible individuals in 

order to spread throughout a host 

population (Townsend et al. 2000). 

Laysan periodically harbors high duck 

densities, which could create a threshold 

population size for density-dependent 

diseases. A severe epizootic could 

diminish the population to the point at 

which demographic stochasticity could 

cause extinction (Mangel and Tier 

1994). 

Echinuriasis (Factor C). 

Echinuria uncinata, a roundworm 

(nematode) that infests the gizzard 

(proventriculus), can be extremely 

pathogenic to waterfowl, although 

susceptibility varies among species. 

This parasite causes tumor-like nodules 

on the proventriculus, resulting in 

blockage and compaction of the 

digestive tract (Cornwell 1963). Laysan 

ducks are susceptible to E. uncinata

infestations. In other ecosystems, 

various crustaceans may serve as 

intermediate hosts for this parasite, 

including amphipods (Gammarus spp.), 

isopods (Asellus aquaticus), cladocerans 

(Daphnia spp.), and conchostracans 

(Lynceus brachyurus) (Austin and 

Welch 1972, Anderson 1992), but the 

intermediate host on Laysan is 

unknown. In Europe and North 

America, E. uncinata infestations occur 

in stagnant freshwater pools with high 

waterfowl densities (Cornwell 1963, 

Austin and Welch 1972). Laboratory 

studies of infected mallard ducklings 

demonstrated that birds stressed by 

crowding had larger parasites and higher 

parasite loads (Ould and Welch 1980). 

On Laysan as well, a severe outbreak in 

1993 coincided with drought and high 

population density. It is likely that only 

one or two stagnant freshwater seeps 

were available to the birds; crowding 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part I: Introduction and Overview. 

36

around these resources may have 

increased disease transmission (Friend 

and Franson 1999). During the 

epizootic, which lasted from August 

1993 to January 1994, the carcasses of 

48 adult ducks were found around the 

lake. Starvation and echinuriasis were 

identified as the causes for mortality 

based on 16 specimens suitable for 

examination (USFWS data, NWHRC 

1993). It is estimated that the Laysan 

duck population dropped from more 

than 600 to approximately 100 adult 

birds during this time period (David and 

Hunter 1994, Reynolds 2002). 

The prevalence of parasitic 

nematodes in the population is 

unknown, but such nematodes have 

been associated with adult or duckling 

mortality in 1993, 1998, and 1999 

(NWHRC 1993, 1998, 1999, 2000). 

Fresh fecal samples (n = 26) collected 

from 20 live birds in the years 1998 

through 2000 were screened for 

parasites. Preliminary analysis showed 

that four of these birds (27 percent of 

samples) were infected with E. uncinata. 

Tapeworm (cestode) eggs were found in 

18 birds (81 percent of samples) (USGS, 

unpublished data). Eggs of four 

unidentified parasite taxa were also 

detected (T. Work, pers. comm. 2000). 

Additional sample analysis and research 

is needed to assess the prevalence of 

echinuriasis and other parasites in the 

population and evaluate their potential 

impacts. 

Other diseases (Factor C). 

Laysan lies in the Pacific flyway and is 

often visited by continental migrants. 

Migratory waterfowl passing through 

the island could introduce diseases to 

which Laysan ducks may have low 

resistance. Avian malaria, a disease 

devastating to Hawaiian passerines 

(songbirds), may have been introduced 

to the Hawaiian Islands by migratory 

waterfowl (Warner 1968). Hawaiian 

birds evolved in the absence of many 

diseases that are common elsewhere and 

may have lower resistance compared to 

their mainland counterparts (van Riper 

and van Riper 1985). A new disease 

introduced to Laysan could cause an 

epizootic in the duck population. The 

Laysan duck’s susceptibility to duck 

plague, avian cholera, and other 

infections that damage waterfowl 

populations elsewhere is unknown. The 

accidental introduction of new disease 

vectors and hosts could be very 

damaging. The first documented case of 

avian botulism was discovered in the 

carcass of an adult duck in 2003 (T. 

Work, pers. comm. 2003); this disease 

could potentially devastate the Laysan 

duck population. 

Environmental Stochasticity and 

Catastrophes 

Catastrophes are rare, irregularlyoccurring events that may cause extreme 

changes in populations. The Laysan 

duck is currently vulnerable to three 

types of environmental catastrophes: 

severe droughts, major storms (such as 

hurricanes), and tsunamis. In addition, 

any of the anthropogenic threats listed 

could be catastrophic if severe enough.
Laysan Duck Draft Revised Recovery Plan, August 2004. Part I: Introduction and Overview. 

37

Drought (Factor E). Population 

monitoring from 1991 through 2001 

suggests that droughts negatively affect 

reproduction and, sometimes, adult 

survival. El Niño Southern Oscillation 

events can disrupt normal rainfall 

patterns, causing droughts in some 

years. El Niño Southern Oscillation 

events in 1987, 1993, and 1998 resulted 

in droughts on Laysan that caused 

reproductive failure (Marshall 1989b, 

Reynolds 2002). In 1993, during a 

period of high population density, 

Laysan experienced its worst drought in 

20 years, resulting in a severe die-off of 

adult birds (see Disease, above). Lake 

levels shrank to their lowest levels since 

1973 (USFWS data). Not only would 

fresh water availability be limited, but 

the abundance of insect prey that form 

the bulk of the Laysan duck’s diet would 

be sharply reduced under such drought 

conditions. 

Severe storms (Factor E). 

Tropical depressions and hurricanes are 

frequent events in the western Pacific 

Ocean. Laysan is a low-lying island 

lacking protection from high winds and 

waves. A hurricane could devastate the 

duck population. Storms have reduced 

breeding success in recent years 

(Moulton and Marshall 1996, Reynolds 

2002). 

Tsunamis (Factor E). Tsunamis 

are series of long waves generated in a 

body of water by an impulsive 

disturbance, such as an earthquake, 

volcanic eruption, or landslide. 

Tsunamis occur in all oceans but are 

most common in the Pacific due to the 

high level of geologic activity in the 

region. The last Pacific-wide tsunami 

occurred in 1964. Tsunamis travel 

rapidly (up to 805 kilometers [500 

miles] per hour) across open ocean and 

upon reaching land can develop wave 

heights of up to 16.6 meters (55 feet; 

Pacific Tsunami Museum 2001). A 

wave of that magnitude would be higher 

than the island of Laysan. Though no 

records exist of tsunamis yet hitting the 

island (a warning of a tsunami likely to 

hit Laysan was issued in 2003), the 

possibility further emphasizes the risks 

faced by the sole remaining population 

of the Laysan duck. 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part II: Recovery Strategy. 

38

II. RECOVERY STRATEGY 

The greatest current threat to the 

Laysan duck population is its reduction to 

a single population of limited size on a 

low-lying island vulnerable to catastrophic 

events. Ensuring the long-term viability 

of the Laysan duck depends upon 

maintaining this source population and its 

habitat on Laysan Island and establishing 

multiple new populations on additional 

islands. The immediate goal is to reduce 

the threats to the Laysan duck to the point 

that we can consider downlisting the 

species from endangered to threatened 

status. The long-term goal is to recover 

the species and ensure that the threats to 

its persistence have been reduced so that it 

no longer requires protection under the 

Endangered Species Act and may be 

delisted. This plan outlines the recovery 

actions that will reduce the risk of 

extinction for the Laysan duck by 

addressing the threats to the Laysan 

population, protecting and enhancing 

habitat quality, and reestablishing 

additional wild populations on other 

islands that are managed to ensure the 

long-term viability of those populations. 

A. Past and Current Conservation 

Measures 

A comprehensive restoration plan has 

been developed for Laysan Island (the 

Laysan Island Ecosystem Restoration 

Plan) that details the measures necessary 

to restore the ecosystem: weed control; 

alien invertebrate identification and 

control; vegetation, invertebrate, and 

vertebrate monitoring; propagation and 

outplanting of native plants; plant and 

invertebrate restoration; pollen core 

studies; vertebrate restoration (including 

the Laysan duck); and snake-eyed skink 

eradication (Morin and Conant 1998). 

Funding, time, and logistical constraints 

have prevented initiation of most of 

these projects, although some are 

underway. This section presents those 

restoration projects and monitoring 

efforts directed specifically at the 

Laysan duck. Recommendations for 

further recovery actions specifically 

geared to benefit the duck are presented 

in later sections of this recovery plan. 

1. Laysan Duck Population 

Monitoring 

The Laysan duck is a difficult 

species to monitor (Sincock and Kridler 

1977). The duck’s nocturnal and cryptic 

habits and seasonal differences in their 

use of the lake contribute to the 

difficulty of estimating the population 

size. Line transect methods are 

unsatisfactory because of the negative 

impact on the ducks (e.g., flushing 

incubating females from nests, leaving 

eggs vulnerable to predators; Marshall 

1992b) and the tendency to 

underestimate the population size 

(Sincock and Kridler 1977, Moulton and 

Weller 1984, Marshall 1992b). Other 

negative effects of line transects include 

the inadvertent destruction of seabird 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part II: Recovery Strategy. 

39

burrows and disturbance of other groundnesting birds. 

Lake counts were used to index the 

population size in the last century and as 

recently as 1998. Direct lake counts are 

not an effective method to estimate 

population size because use of the lake by 

Laysan ducks is seasonally and 

environmentally variable. It is not possible 

to calculate the relationship between direct 

counts and the total population size. 

Marshall (1992b) and others determined 

that the most accurate way to monitor the 

population is by calculating ratios of 

marked to unmarked ducks at the lake at 

dusk. Fall and spring yield the highest 

numbers of lakeside ducks for population 

estimates, although year-round monitoring 

is ideal. This method requires that a 

portion of the population be marked. A 

percentage of the population should be 

banded by qualified personnel once a year. 

Two different monitoring methods are 

now used twice each month: census walks 

and resighting surveys. Field staff 

determine the ratio of marked to unmarked 

Laysan ducks during a 1-hour census walk 

around the lake before sunset. Birds are 

recorded as banded, unbanded, or 

unknown. The numbers of broods and 

ducklings and the age class of ducklings 

are recorded. 

A known percentage of the Laysan 

duck population is currently marked with 

color bands. Individuals have unique 

band combinations. Resighting surveys 

provide data that can be used to determine 

population parameters such as 

survivorship, sex ratio, individual 

histories, brood production and breeder 

identification. Band reading is 

conducted for 1 to 2 hours before sunset. 

Observers note the sex and band 

combination of each bird. All ducklings 

and hens are identified, and the 

ducklings are assigned an age class. 

The geographic isolation of the 

Laysan duck on a small island makes it 

well suited to a mark-resight method of 

population estimation such as the 

Lincoln-Peterson Index (see Table 2), as 

the population meets the “closed 

population” assumption of such a 

model. There is no possibility of 

emigration or immigration, and during 

intensive monitoring and with high adult 

survivorship in this species, the markresight methods meet the assumption of 

no births or deaths in the population as 

well (Bibby et al. 1992). 

2. Ecosystem Conservation and 

Monitoring 

Weed control and vegetation 

monitoring 

In 1991 we initiated a program to 

eradicate the nonnative grass Cenchrus 

echinatus on Laysan Island. Full-time crews 

of one or more technicians have maintained 

these eradication efforts year-round. C. 

echinatus is highly invasive, forming dense 

mats that crowd out the native bunchgrass 

Eragrostis variabilis, which is the preferred 

nesting habitat for the duck on Laysan. 

Eradication efforts have been highly 

effective. No C. echinatus has been found 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part II: Recovery Strategy. 

40

on Laysan since April 2002 (USFWS data 

2002, 2003). 

Native plant propagation and 

outplanting 

Beginning in 1999, seeds of the 

endangered plant Mariscus pennatiformis 

ssp. bryanni were collected and 

propagated on Laysan. Seeds and cuttings 

of another endangered plant, 

Chenopodium oahuense, also were 

gathered. Seeds of the native palm 

Pritchardia remota were obtained from 

Nihoa Island and taken to Laysan for 

propagation, and work has begun on the 

propagation of the bunchgrass Lepturus 

repens (Depkin and Lund 2001). Current 

native plant propagation efforts on Laysan 

include the following species: Capparis 

sandwichiana, Chenopodium oahuense, 

Lepidium bidentatum var. o-waihiense, 

Lepturus repens, Mariscus pennatiformis

ssp. bryanni, Pritchardia remota, 

Santalum ellipticum, and Solanum 

nelsonii. 

Invertebrate monitoring 

Arthropod sampling and identification 

were conducted opportunistically in 1999 

and 2000 by Reynolds and Nishida 

(Nishida 1999, Nishida 2000). Continued 

incursion of alien arthropods was 

documented. 

Ant control experiment 

We initiated a pilot project to remove 

introduced ants from Spit Island, Midway 

Atoll, in 2001 and 2002. Fire ants 

(Solenopsis geminata) were thought to 

be eliminated but began to reappear 1 

year after the pesticide was applied (C. 

Swenson, pers. comm. 2002). As 

Midway is under consideration as a 

potential reintroduction site for the 

Laysan duck, the successful eradication 

of fire ants prior to translocation would 

be beneficial to the success of that 

program. Methods to eradicate ants 

from other islands would improve 

opportunities for ecosystem restoration, 

which would also benefit Laysan ducks. 

Lake and brine fly sampling 

Every other week the salinity, water 

temperature, and water depth are 

measured in the lake at the permanent 

depth gauge along the east edge, as well 

as in two adjacent freshwater seeps

(USFWS 2001). A hydrological 

assessment would benefit freshwater 

seep restoration efforts as well as 

aquifer use by the field camps. Brine 

flies are monitored as an index of food 

abundance for the duck. Fly abundance 

at the lake may serve as a predictor of 

duck breeding. 

3. Captive Populations 

In the late 1950’s, 33 ducks were 

removed from Laysan and transferred to 

captive breeding facilities around the 

world. Offspring from those birds were 

used to found a colony at the Pohakuloa 

Endangered Species Facility in Hawai`i, 

and seven wild Laysan ducks were later 

added to that flock in an effort to 

improve breeding. The birds produced 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part II: Recovery Strategy. 

41

by this program were unsuitable as 

candidates for reintroduction to the wild 

due to poor breeding records and possible 

hybridization in captivity, consequently 

the captive breeding of Laysan ducks was 

discontinued in Hawai`i in 1989. Some of 

the birds were shipped to mainland 

facilities, and individuals older than 8 

years were euthanized (Reynolds and 

Kozar 2000b). 

Surveys of zoos and private 

collections in 1999 indicated that 211 

Laysan ducks were held in 32 collections 

worldwide, all descended from fewer than 

19 founding pairs (Reynolds and Kozar 

2000b). Initially, birds bred well in 

captivity, but over time breeding success 

has decreased, possibly as a result of 

inbreeding depression. Average clutch 

size for captive broods declined from 7.3 

eggs in 1984 (Marshall 1992b, Moulton 

and Marshall 1996) to 4.9 in 1999 

(Reynolds and Kozar 2000a). Some 

captive populations may also suffer from 

genetic “pollution”; birds have been kept 

in mixed flocks, and Laysan ducks in three 

facilities are known to have hybridized 

with a koloa, a northern shoveler (Anas 

clypeata), a cinnamon teal (Anas 

cyanoptera), and a wood duck (Aix 

sponsa). Only 15 percent of facilities 

surveyed kept pedigrees for their Laysan 

ducks (Reynolds and Kozar 2000a). 

4. Pearl and Hermes Reef 

Translocation 

Aware of the threats facing the Laysan 

duck population, biologists attempted to 

establish a new population on Pearl and 

Hermes Reef, approximately 440 

kilometers (273 miles) northwest of 

Laysan (see Figure 2). In March of 

1967, five males and seven females 

were captured on Laysan Island and 

transported to Pearl and Hermes Reef 

for release. The first two birds released 

flew directly out to sea and disappeared. 

The remaining 10 ducks had their wings 

clipped to prevent flight until after the 

annual molt (Berger 1981). An 

expedition in May discovered two dead 

Laysan ducks, cause of death unknown. 

In July a female was found incubating a 

nest of six eggs, but the nest later failed. 

Only two ducks were seen during a visit 

to the island in September of that year, 

and none were seen on successive trips 

(Sincock and Kridler 1977). Inadequate 

monitoring of the released birds 

prevented identification of causes for 

failure. However, we suspect a 

combination of factors doomed the 

effort: the release methods, marginal 

habitat, the small number of founding 

birds, and stochastic factors. No further 

translocations have been attempted since 

this time. 

B. Translocation 

Translocation is the deliberate 

release of animals to the wild to 

establish, reestablish, or augment a 

population (Griffith et al. 1989). It is 

used as a conservation tool to mitigate 

threats to a species by placing 

individuals at locations that are free of 

those threats, as a short-term or longterm means of increasing a species’ 

chance of survival, or as part of a 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part II: Recovery Strategy. 

42

program to restore a particular biotic 

community. There is an urgent need to 

translocate Laysan ducks to additional 

islands and establish new populations, 

especially for the first two of these 

reasons. The restoration of the Laysan 

duck as a component of the native 

ecosystems on these islands is also 

desirable. 

1. Justification for Immediate 

Translocation 

The discovery of Laysan duck bones 

on the Main Hawaiian Islands and our 

knowledge that it previously inhabited 

Lisianski Island provides a sound 

biogeographic foundation for establishing 

Laysan duck populations on additional 

islands (Olson and Ziegler 1995, Cooper 

and Anderson 1996). Ecosystem 

restoration and the reestablishment of 

additional wild Laysan duck populations 

on other islands are needed to reduce the 

risk of extinction. These duck populations 

would also represent the restoration of a 

missing component of the Hawaiian 

avifauna on these islands. In 2000 a 

feasibility study was carried out to 

evaluate the possible translocation of 

Laysan ducks to other sites (Reynolds and 

Kozar 2000a). It was predicted that 

restoration of Laysan ducks to additional 

islands may: 

i. reduce overcrowding on Laysan 

during periods of high population 

density through ongoing 

translocations; 

ii. reduce the risk of extinction from 

stochastic events that affect the 

single population on Laysan; and 

iii. restore the species to 

ecosystems where it previously 

existed. 

The Laysan duck is an excellent 

candidate for translocation. The species 

is adapted to a harsh environment, 

flexible in its foraging behavior, large 

enough to carry radio transmitters with 

high battery capacity (to facilitate 

monitoring of released birds), and the 

flight feathers can be trimmed to prevent 

dispersal from the release site. On a 

predator-free island, clipping flight 

feathers would not compromise the 

duck’s survival, foraging, or breeding, 

and the feathers would be replaced with 

the next molt. With adequate food, 

water, cover, and protection from 

mammalian predators, the Laysan duck 

breeds well in the wild. The birds are 

unlikely to affect rare invertebrate 

populations at translocation sites, as 

they seem to select the most abundant 

prey available (Reynolds 2002). 

2. Hybridization and 

Introgression 

Hybridization is the interbreeding of 

individuals from genetically distinct 

populations, and introgression is gene 

flow between populations of individuals 

that hybridize (Rhymer and Simberloff 

1996). There is some concern that 

Laysan ducks might hybridize with 

koloa or mallards. Hybridization and 

introgression with mallards has 

contributed to the decline of other duck 

species in New Zealand, Australia, and 

the United States (notably the koloa; 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part II: Recovery Strategy. 

43

Rhymer and Simberloff 1996). However, 

Laysan ducks have not hybridized often in 

captivity, they are genetically distinct 

from mallards and koloa (Rhymer 2001), 

and they may have co-existed with koloa 

on the main islands in the past, all factors 

that suggest Laysan ducks are less likely 

to hybridize in the wild (Reynolds and 

Kozar 2000a, Pratt and Pratt 2001). As a 

precaution, mallard populations should be 

controlled at translocation sites to prevent 

hybridization of mallards with either of 

the native endangered duck species. 

3. Source Population 

The existing captive flocks of Laysan 

ducks are unsuitable for release into the 

wild because the pedigrees of these birds 

are unknown. Studbooks have not been 

maintained, careful breeding to maintain 

genetic diversity has not taken place, and 

Laysan ducks have been kept in mixedspecies flocks and have possibly 

hybridized with other species (see 

Prospects for Reintroduction of Captive 

Birds, below). Until a new captive 

population is created that is managed 

specifically for the purpose of establishing 

additional wild populations, only wildsource individuals should be used for 

translocation (Reynolds and Kozar 

2000a). Translocation success with wildcaught animals often is greatest from high 

density and increasing source populations 

(Griffith et al. 1989). These conditions 

are rare for endangered species, but such 

conditions do occur periodically in the 

duck population on Laysan Island. 

Of primary concern to managers, 

then, is the population trend on Laysan 

and whether the population can 

withstand the removal of individuals to 

reestablish the species elsewhere in 

Hawai`i. The best age class and the 

number of ducks to remove from the 

source population were explored with 

population simulations for several 

removal scenarios using the RAMAS 

AGE program (version 2.0; Reynolds 

and Kozar 2000a). The program 

simulates age-structured population 

fluctuations and can be applied to 

predict population size and persistence. 

Simulations incorporating translocation 

removals show that removal of up to 20 

percent of juvenile birds for 5 years had 

the least significant impact on 

population projections. Removal of 

breeding birds accelerated the time to 

extinction and caused a greater decline 

in the population than removal of

juveniles. Removal of adult females 

from Laysan, especially during periods 

of lower population density, could 

exacerbate decline in the source 

population by decreasing production. 

Juveniles from the Laysan source 

population should be removed during 

periods of high population density or 

during periods of population growth. 

Additional research is needed to 

determine causes for the low number of 

females breeding successfully and the 

high levels of duckling mortality 

currently observed. Limited brood 

rearing habitat is suspected to increase 

mortality from overcrowding. 

Management to increase duckling 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part II: Recovery Strategy. 

44

survival should be explored to ameliorate 

the possible negative effects of removals 

for translocation and to provide more 

juveniles for translocation. 

4. Transfer Population 

The best practices to prevent genetic 

drift within a transfer population are to 

maximize the number of founding 

individuals and to add new birds regularly 

from the source population. A minimum 

of 50 randomly selected founders is 

recommended to maintain short-term 

fitness (Franklin 1980). If few individuals 

are available, selection criteria will depend 

on how many high-quality birds of the 

proper age and sex classes are available. 

Additional founding birds could be 

introduced from subsequent years’ recruits 

for each translocation site. Further 

population supplementation may 

occasionally be required to increase 

population growth and to maintain or 

improve genetic variability. On Laysan, 

reproduction is highly variable, and few or 

no ducklings are produced in some years, 

so planning for multi-year translocations 

is required. 

The age and sex of the translocated 

birds are important variables in producing 

a self-sustaining population. As 

mentioned above, fledged juveniles would 

be the preferred candidates for 

translocation, based on analysis of 

population fluctuation. Also, an equal or 

slightly male-biased ratio would be 

preferable, as a slight bias toward males 

promotes male-male competition and 

female choice, an important stimulant for 

breeding activity in many dabbling duck 

species (McKinney and Brewer 1989). 

Birds selected for translocation 

should be treated for echinuriasis and 

other diseases before removal to the 

transfer sites. Echinuria is unknown in 

waterbirds in the Main Hawaiian 

Islands, and the risk to those populations 

would be substantial if juvenile birds 

from Laysan harboring the parasite were 

transferred to the main islands either for 

release or for propagation of a captive 

flock (T. Work, pers. comm. 2002). The 

anti-parasite medication ivermectin is 

known to eliminate nematodes in other 

waterfowl, and has been used 

successfully in other endangered duck 

species during translocation in New 

Zealand (Gummer 1999), but the 

potential toxicity of this drug to Laysan 

ducks is not known. Safety trials should 

be conducted on Laysan ducks to 

determine if they will react adversely to 

ivermectin (T. Work, pers. comm. 

2002). 

We recommend a “soft” release, in 

which birds are gradually acclimated to 

their environment in an on-site 

enclosure. This type of release reduces 

stress on birds and increases site fidelity, 

lowering the chance of birds dispersing 

from the release site (Kleiman 1989). 

An aviary on or near the release site 

would be ideal for temporarily housing 

translocated birds. Laysan ducks do 

well in captivity and should easily adjust 

to aviary life. Birds are known to be 

aggressive towards one another, 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part II: Recovery Strategy. 

45

therefore separate pens maybe required for 

some. 

5. Selecting and Evaluating the 

Release Site 

For a translocation to be successful, 

the primary threats that led to the species’ 

initial decline or extirpation must be 

controlled. Poor habitat quality is the 

most common reason for the failure of 

translocations (Griffith et al. 1989, Veitch 

1995). In the case of the Laysan duck, 

mammalian predators on the main islands 

and competitors on the Northwestern 

Hawaiian Islands were the primary 

limiting factors and need to be controlled 

at proposed translocation sites. Sufficient 

food, water sources, cover, and breeding 

sites also must be available at the release 

location. 

Despite the duck’s prehistoric 

distribution in forested areas of the Main 

Hawaiian Islands, only habitats where 

mammalian predators are absent or 

sufficiently controlled should be 

considered for translocation sites. The 

presence of predators would seriously 

jeopardize the success of any translocation 

effort (Armstrong and McLean 1995, 

Veitch 1995, Towns et al. 1997). Possible 

methods for control of predators at 

translocation sites on the Main Hawaiian 

Islands include fences, toxicants, trapping, 

shooting, or some combination of these. 

Predator exclusion fences are under 

development but not yet in regular use in 

Hawai!i; research and trials are taking 

place, however, in Hawai!i, New Zealand, 

and elsewhere in the Pacific. In addition, 

even the predator-free islands of the 

Northwestern Hawaiian Islands will 

require some restoration in the form of 

pest and weed control, or freshwater 

seep creation or restoration. 

Site visits were made to areas where 

Laysan ducks might be reintroduced 

(Reynolds and Kozar 2000a). 

Biological characteristics and nonbiological suitability features of these 

sites are summarized in Appendices 1 

and 2. Biological factors considered 

included habitat assessment, vegetation 

characteristics, invertebrate abundance, 

fresh water presence or absence, 

potential predators, and the need for 

restoration and/or predator control 

efforts. Non-biological features 

included physical characteristics of the 

island, logistical feasibility (e.g., ease of 

post-release monitoring), and existing 

infrastructure or management. Twelve 

Northwestern Hawaiian Islands and 8 

Main Hawaiian Islands were assessed in 

terms of their suitability for the 

reestablishment of Laysan duck 

populations (Appendix 1). Of the 20 

islands considered, 6 were considered 

promising potential translocation sites: 

Eastern Island (Midway Atoll National 

Wildlife Refuge), Lisianski Island and 

Nihoa Island (Hawaiian Islands National 

Wildlife Refuge), and Kure Atoll (City 

and County of Honolulu) in the 

Northwestern Hawaiian Islands, and the 

islands of Kaho`olawe and Kaua`i in the 

Main Hawaiian Islands (Appendix 2). 

Descriptions of these islands and brief 

discussions of their biological and 

physical suitability and management 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part II: Recovery Strategy. 

46

needs as translocation sites are presented 

below (not in order of priority). 

It is critical to note here that 

augmentation of these discussions with 

fiscal and management assessments is 

necessary to develop a prioritized list of 

translocation sites and to select an initial 

site where translocation will be most 

feasible, cost-effective, and likely to 

succeed. Working in such a remote island 

chain, the realities of translocation and 

reestablishment efforts are that logistical 

feasibility and cost will play an important 

role in site selection. 

Northwestern Hawaiian Islands 

Midway Atoll. Midway Atoll lies at 

28° 12’ N, 177° 22’ W, approximately 

1,840 kilometers (1,143 miles) northwest 

of Honolulu (Figure 1). The atoll’s land 

area covers 625 hectares (1,544 acres) and 

is composed of two main islands, Sand 

Island (467 hectares [1,154 acres]) and 

Eastern Island (156 hectares [385 acres]), 

and a smaller islet, Spit Island (2 hectares 

[5 acres]). Like Laysan, Midway Atoll is 

a National Wildlife Refuge managed by 

our agency and is surrounded by waters 

included in the Northwest Hawaiian 

Islands Coral Reef Ecosystem Reserve 

managed by the National Oceanic and 

Atmospheric Administration. 

 

For many logistical reasons Eastern 

Island at Midway Atoll may be an 

excellent site for a trial release of Laysan 

ducks. Midway is home to permanent 

personnel with our agency and can support 

expensive chartered air service from 

Honolulu. Rehabilitation of habitat on 

Midway is therefore more logistically 

feasible than it would be on an 

uninhabited island. Eastern Island has 

no human settlements and fewer 

anthropogenic hazards than Sand Island, 

and could be the best location in the 

atoll for an experimental release. 

Midway has experienced many 

introductions of nonnative plant species 

over the years, including Verbesina

encelioides and C. echinatus. Efforts 

are currently underway to control these 

exotics. The invertebrate fauna on 

Midway Atoll is dominated by exotics. 

On Eastern Island, intensive introduced 

weed control, particularly of V.

encelioides and C. echinatus, is 

recommended. Vegetation restoration 

can take place after release of Laysan 

ducks, but if broad-scale herbicides, 

pesticides, and heavy equipment are 

used, Laysan ducks could be negatively 

affected. Fire ants and big-headed ants 

also should be controlled, or else 

supplemental feeding of translocated 

birds may be needed until techniques for 

removal of the ants are developed (or 

their impacts on the duck’s prey base 

and nests are judged to be insignificant). 

Predatory arthropods such as the 

big-headed ant may need to be 

controlled; other introduced 

invertebrates likely would be prey items 

for the Laysan duck (Reynolds and 

Kozar 2000a). Fire ants (Solenopsis

geminata) were discovered on Midway 

Atoll in 2000. Results of a pilot project 

to eradicate ants from Spit Island using 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part II: Recovery Strategy. 

47

bait treated with the toxicant Maxforce 

(hydramethylon) indicate that fire ants can 

be controlled by periodic (possibly 

annual) applications of granular ant 

toxicants (C. Swenson, pers. comm. 

2001). 

Currently no permanent standing 

sources of fresh water exist on Eastern 

Island. Wetland creation and watering 

devices are a necessary prelude to release 

of Laysan ducks on Eastern Island. 

Multiple sources of fresh water are 

recommended. In August 1999 and 2001, 

biologists traveled to Midway to evaluate 

the atoll as a potential release site for 

Laysan ducks, and specifically to evaluate 

the creation of wetland habitat to provide 

a source of fresh water (Reynolds and 

Kozar 2000a; A. Engilis, pers. comm. 

1999; S. Reilly, pers. comm. 2001). The 

water table is less than 2 meters (6.6 feet) 

below the land surface in some parts of the 

atoll, providing suitable conditions for the 

potential creation of a wetland. Wetland 

and vegetation restoration would improve 

opportunities for successful establishment 

of self-sufficient, self-sustaining wild 

populations of ducks. 

Translocation of ducks to a temporary 

aviary setting on Sand Island in 

preparation for a soft release to Eastern 

Island can occur simultaneously with 

habitat restoration efforts. Intensive 

management of Laysan ducks at 

translocation sites, such as the provision 

of supplemental food and water, may be 

required until restoration efforts are 

complete. 

Lisianski Island. Lisianski Island 

is Laysan’s nearest neighbor in the 

northwest Hawaiian chain, and is known 

to have previously supported a 

population of Laysan ducks. Loss of 

plant cover in the mid-1800’s resulted in 

shifting sands that filled the island’s 

fresh water source. Since Laysan ducks 

existed previously on Lisianski, we 

know that with adequate management 

the island can support a population of 

the birds, thus Lisianski is a potential 

translocation site. In the event that 

Lisianski is chosen as a translocation 

site for Laysan ducks, wetland habitat 

must be restored, and development of a 

Lisianski ecosystem restoration plan is 

recommended. The restoration of the 

wetland on Lisianski would pose 

logistical challenges, as the remote 

location of the island would preclude the 

transport and use of the construction 

equipment that would normally be used 

for such an operation. 

Nihoa Island. Nihoa Island also is 

considered a potential translocation site 

after experimental translocations are 

made to other islands. At 68 hectares 

(168 acres), the island is large enough to 

support a small population of the birds. 

Native plants and arthropods are 

abundant. Freshwater seeps occur 

naturally on Nihoa, eliminating the need 

to provide water sources or other 

restoration for Laysan ducks. Nihoa is 

considered the most pristine of the 

Northwestern Hawaiian Islands, and an 

assessment of the potential impacts of 

Laysan ducks on the island’s terrestrial 

biota should be conducted prior to 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part II: Recovery Strategy. 

48

translocation (Reynolds and Kozar 

2000a). For example, the endemic coneheaded katydid Banza nihoa already may 

be negatively affected by the introduced 

grasshopper Schistocerca nitens and 

perhaps by several ant species, and the 

risk of predation by Laysan ducks should 

be considered (E. Flint, pers. comm. 

2002). We suspect, however, that human 

impacts to Nihoa (associated with a 

translocation effort) are the primary risk. 

Technology for remote or automated postrelease monitoring to eliminate the need 

for human presence on Nihoa should be 

explored. 

Kure Atoll. Kure Atoll consists of 

three separate islets comprising 100 

hectares (247 acres) of land area. Kure 

Atoll once supported a U.S. Coast Guard 

LORAN (long range navigation) station, 

but little or none of the infrastructure 

remains. The atoll is managed by the 

State of Hawai`i, which eliminated rats on 

the islets in 1994 and has initiated a weed 

eradication program to control the spread 

of V. encelioides. The islands support a 

large number of arthropods and have a 

moderate amount of nesting cover for 

ducks. Sources of fresh water, perhaps 

from rainwater catchments, could be 

created to sustain a Laysan duck 

population there (Reynolds and Kozar 

2000a). 

Main Hawaiian Islands 

Kaho`olawe. Kaho`olawe would be 

an ideal site for translocation of Laysan 

ducks to a main Hawaiian island. 

Translocation of Laysan ducks to 

Kaho`olawe already has been 

recommended by the Kaho`olawe Island 

Restoration Commission (Social Science 

Research Institute 1998). A former U.S. 

Navy bombing range, the island was 

transferred to the State of Hawai ́i in 

1994, and for the past 10 years the Navy 

has been working to remove any 

remaining live ordnance and meet the 

State’s objectives for preservation of 

archeological sites and environmental 

restoration on Kaho ́olawe. Goats have 

been removed, ordnance removal is near 

complete, and botanical restoration is 

underway on the island, which now 

supports moderate nesting cover and a 

wide variety of arthropods. The Navy’s 

work on Kaho`olawe is expected to be 

completed in 2004. Ephemeral wetlands 

exist on the island but need 

enhancement. Rats have not been seen 

on the island since 1971, leaving cats as 

the only mammalian predator. If cats 

were removed, Kaho`olawe would have 

excellent potential as a release site 

(Reynolds and Kozar 2000a).

Kaua`i. Of the other Main 

Hawaiian Islands, Kaua!i may be the 

best choice for reintroduction of the 

Laysan duck because it is the only island 

that is believed to be free of the Indian 

mongoose, a predator that would pose a 

major risk to a translocated duck 

population. Other significant predators, 

including rats, cats, and dogs, occur on 

the island and would have to be 

controlled prior to a release of ducks 

(and probably in perpetuity). Multiple 

sites on Kaua`i could be suitable for 

Laysan duck release (see Appendix 1), 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part II: Recovery Strategy. 

49

including two existing National Wildlife 

Refuges. These sites have extensive areas 

of suitable habitat and nesting cover and 

abundant sources of food and fresh water. 

Other Main Hawaiian Islands 

Ni`ihau, O`ahu, Maui, Moloka`i, 

Lana`i, and Hawai`i all have sites that 

potentially could support Laysan ducks. 

Managed wetlands occur on O`ahu, Maui, 

and Hawai`i; of the five islands listed 

above, these three may provide the best 

opportunities for establishing Laysan duck 

populations. All of these islands, 

however, have significant problems with 

introduced mammalian predators which 

would have to be addressed through either 

control efforts or exclosures before they 

could be considered as translocation sites 

for Laysan ducks. 

6. Prospects for Reintroduction of 

Captive Birds 

General Issues 

The original Laysan duck recovery 

plan recommended maintaining captive 

flocks bred to ensure pure strains for 

eventual reintroduction to the wild 

(USFWS 1982). Unfortunately, this plan 

was never realized. Hybridization, 

incomplete population statistics, and 

harmful genetic change in captivity make 

the existing captive ducks and their future 

offspring poor candidates for 

reintroduction (Reynolds and Kozar 

2000b). Genetic change in a captive 

environment can decrease reintroduction 

success in two ways: 1) genetic variation 

may be lost through limited breeding 

opportunities, and 2) animals may 

become adapted to the captive 

environment (Frankham 1994). In zoos, 

natural selection pressure on many 

features required for survival in nature, 

such as hunting and foraging abilities, is 

relaxed. Over long periods in captivity, 

natural selection acts to maximize 

fitness in a captive environment, thus 

the individuals surviving and breeding 

are those pre-adapted to captive 

conditions. A review of translocation 

efforts for various animal species from 

1973 to 1986 found a vastly different 

success rate between wild-caught (75 

percent) and captive-reared (38 percent) 

individuals (Griffith et al. 1989). 

Captive breeders can minimize 

genetic adaptations to captivity by 

specifically managing captive flocks for 

reintroduction to the wild. Techniques 

to minimize genetic changes include 

reducing time spent in captivity, 

regularly introducing wild genes, using 

only the offspring of wild birds for 

release, and releasing birds into wild or 

semi-wild habitat temporarily, until 

suitable habitat within their previous 

range can be restored (Frankham 1994, 

Reynolds and Kozar 2000b). 

Disease is an additional risk in 

translocating captive-reared birds, 

especially birds from mainland facilities. 

Confinement and mixing with other 

birds often increases the likelihood of 

disease transmission in captive flocks 

(Friend and Thomas 1990). Monitoring, 

examination, and treatment of birds are 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part II: Recovery Strategy. 

50

essential to protect captive breeding 

programs. These measures have not been 

adopted for captive Laysan duck 

populations, further reducing their 

suitability as candidates for wild release. 

The Avian Disease Working Group, an 

association of captive breeders and 

veterinarians, rejected the idea of 

reintroducing captive mainland birds to 

Hawai`i based on logistical, fiscal, and 

quarantine restraints (C. Kuehler, pers. 

comm. 2000). 

Translocation Planning 

Translocated flocks should consist of 

wild-caught fledged juveniles, kept in an 

aviary in preparation for a “soft” release 

while habitat restoration is underway. We 

do not know if fledgling birds will be 

available for translocation when 

restoration is complete; therefore, birds 

should be removed from Laysan in the 

autumn even if restoration is unfinished 

and released in the spring. Having Laysan 

ducks ready for release may speed up 

restoration efforts. If juveniles are 

available on Laysan, a second cohort can 

be transferred and released the subsequent 

autumn. 

Northwestern Hawaiian Islands. 

We believe it would be feasible to use 

captive-bred birds for introduction to the 

Northwestern Hawaiian Islands if these 

birds came from a new population that 

was specifically managed for such 

releases, but considering the urgency of 

establishing a new wild population, using 

wild, parent-raised fledglings from Laysan 

for reestablishment on other islands in the 

northwestern chain would be more 

expedient, easier logistically, and 

perhaps more successful. It would take 

years before suitable numbers of 

captive-bred offspring would be 

available for release. Disease risks on 

the main islands are higher, and these 

risks may be minimized if translocations 

of birds to islands in the northwestern 

chain are of individuals from other 

northwestern islands.

Main Hawaiian Islands. A captive 

breeding facility, managed for 

establishing additional wild flocks of 

Laysan ducks, is needed in the Main 

Hawaiian Islands. Eggs taken from 

Laysan Island may be the best way to 

found the captive flock because eggs are 

easier to transport than live birds, and 

egg removal would have the least 

impact on the population dynamics of 

the Laysan birds. First-generation (F1) 

offspring from those eggs would be 

released to found the new wild flocks on 

the main islands. 

Translocation of wild birds from 

Laysan for the establishment of wild 

main island populations is also feasible, 

but this possibility is limited by both the 

logistics and the “critical mass” needed 

for the establishment of large viable 

populations without depleting the 

source. If multiple Northwestern 

Hawaiian Islands populations are 

established and they reach carrying 

capacity, subsequent removal of hatchyear Northwestern Hawaiian Islands 

birds for main island populations would 

be a good option. 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part III: Recovery Criteria and Actions. 

51

III. RECOVERY CRITERIA AND ACTIONS 

A. Goal and Objectives 

The goal of the recovery program is 

to conserve and recover species to the 

point at which they can be downlisted 

from endangered to threatened status, 

and ultimately to remove them 

completely from the Federal list of 

threatened and endangered species when 

the protections provided by the 

Endangered Species Act are no longer 

necessary. Downlisting from 

endangered to threatened status is a 

near-term goal for the Laysan duck, and 

delisting or removal from the 

endangered species list is the long-term 

goal. This recovery plan identifies 

actions needed to achieve long-term 

viability for the Laysan duck and 

accomplish these goals. Recovery of the 

Laysan duck focuses on the following 

objectives: 1) management to reduce 

risks to the Laysan Island population, 2) 

protection and enhancement of suitable 

habitat, and 3) actions to reduce or 

eliminate threats sufficient to allow 

successful reestablishment of additional 

wild populations. Accomplishing these 

objectives through the recommended 

actions has the highest likelihood of 

recovering this endangered species. 

The emphasis in this recovery plan 

on the distribution of additional viable 

populations in the Laysan duck’s 

historical range is based upon two 

widely recognized and scientifically 

accepted goals for promoting viable 

populations of listed species. These 

goals are: 1) the creation of multiple 

populations so that a single or series of 

catastrophic events do not result in 

species extinction; and 2) the increase of 

population size to a level where the 

threats from genetic, demographic, and 

normal environmental uncertainties are 

diminished (Mangel and Tier 1994, 

National Research Council 1995, Tear et 

al. 1995, Meffe and Carroll 1997). By 

maintaining population numbers and 

viable breeding populations at multiple 

sites on multiple islands, the Laysan 

duck will have a greater likelihood of 

achieving long term survival and 

recovery. 

Definitions: 

Endangered Species — Any species 

which is in danger of extinction 

throughout all or a significant portion of 

its range.

Threatened Species — Any species 

which is likely to become endangered 

within the foreseeable future throughout 

all or a significant portion of its range. 

B. Recovery Criteria 

At this time we have developed only 

interim downlisting criteria for the 

Laysan duck due to the data limitations 

and potential uncertainties associated 

with attempting to define realistic 

criteria for delisting, particularly in 

regard to target population sizes. 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part III: Recovery Criteria and Actions. 

52

Because our knowledge of Laysan duck 

population biology and ecology is 

restricted to observations from the 

unique environment of Laysan Island, 

we currently have no reliable biological 

basis for setting target population sizes 

for delisting on other islands with very 

different habitats and potential threats. 

Delisting criteria, when developed, must 

be based on new information that can 

only be accumulated as we begin to 

implement the recovery actions outlined 

in this plan and learn about the 

population dynamics and growth rates of 

Laysan ducks in new habitats on islands 

other than Laysan. Thus we believe that 

downlisting is the most conservative and 

scientifically defensible strategy to take 

in this recovery plan until more 

comprehensive information is available. 

Some of the downlisting criteria 

presented below are based on the results 

of population viability analyses (see 

following “Rationale” section). It is 

important to note that such population 

models are management tools based on 

many assumptions and are subject to the 

limitations of existing data describing 

the species’ biology, requirements, and 

habitat. Population viability analyses 

use risk factors to evaluate probabilities, 

not certainties. Therefore, the results of 

such analyses should be interpreted as 

general guidance, not as inflexible goals 

for recovery (Reed et al. 1998). The 

population targets for downlisting 

offered below should be revised after 

translocations take place and we learn 

more about the population dynamics of 

Laysan ducks in new habitats and the 

observed (versus projected) carrying 

capacities of planned translocation sites. 

The development of meaningful 

delisting critiera will also require this 

new data. 

1. Downlisting Criteria 

 

Criterion 1. The Laysan Island 

population is stable or increasing (finite 

rate of population growth or λ greater 

than or equal to 1.0) when averaged 

over a continuous period of at least 15 

years. 

Criterion 2. A total of at least 920 

potentially breeding adult birds exist in 

at least 5 stable or increasing 

populations on a combination of 

predator-free Northwestern Hawaiian 

Islands (including Laysan) and predatorcontrolled sites on the Main Hawaiian 

Islands. The population on Laysan 

Island should remain at a level of from 

400 to 500 birds; the remaining 4 or 

more newly established populations 

should occur on a combination of 

predator-free Northwestern Hawaiian 

Islands and predator-controlled sites on 

the Main Hawaiian Islands, and should 

number approximately 130 breeding 

adult birds each (depending on the size 

of the habitat available on the island). 

Criterion 3. A successful captive or 

semi-captive breeding program is 

established using wild source eggs. 

These captive populations are managed 

primarily for reintroductions to the Main 

Hawaiian Islands. 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part III: Recovery Criteria and Actions. 

53

Criterion 4. A plan for achieving 

gene flow between wild source 

populations through long-term interisland translocations is developed and 

implemented. 

Criterion 5. Island-specific 

management plans for each population 

are created that identify actions (such as 

supplementation, habitat improvement 

and predator control) sufficient to 

reduce threats and increase the 

populations to recovery levels. 

2. Rationale for Downlisting 

Criteria 

Criterion 1. Environmental 

variability will affect Laysan’s annual 

carrying capacity and year-to-year 

demographic rates. Population growth 

thus should be evaluated according to 

the overall trend for a continuous 15-

year period. Current estimates predict 

that El Niño Southern Oscillation events 

will occur approximately every 7 years 

in Hawai`i, thus a 15-year interval will 

allow for periodic population 

fluctuations in response to these events. 

Criterion 2. We used the population 

viability analysis program VORTEX 

(version 8.41, Lacy 1993) to model the 

persistence of the Laysan duck over a 

100-year timeframe under various 

management scenarios. For the 

purposes of downlisting, we chose to 

use as a guide the scenario that predicts 

a 99 percent probability of the species’ 

persistence over 100 years. This 

scenario includes a substantial pool of 

breeding ducks distributed across five 

populations on a combination of three 

Northwestern Hawaiian Islands, 

including the extant population on 

Laysan, as well as two populations on 

the Main Hawaiian Islands (see 

Appendix 3). To persist over the time 

period of 100 years, the model estimated 

a mean final total population size of 611 

birds, ± 309 SD. Due to our limited 

information on the Laysan duck, 

especially in regard to factors such as its 

survivorship and productivity in any 

environment other than that of Laysan 

Island, the input for the population 

model necessarily required some 

assumptions and extrapolations from 

data collected on Laysan, such as the 

estimated carrying capacity for each 

potential translocation site and the 

currently known demographic 

parameters for the Laysan duck on 

Laysan Island. The actual carrying 

capacity of proposed translocation sites 

is unknown, but estimates for the 

VORTEX model were based on the 

carrying capacity of Laysan (one bird 

per 0.5 hectares, assuming 75 percent of 

the island’s area contains suitable 

vegetated habitat; the exception was 

Sand Island, Midway Atoll, for which it 

was assumed that 50 percent of the land 

area was suitable). Because we lack 

information about Laysan duck 

reproductive success, demography, and 

ecology in habitats other than that of 

Laysan Island, we chose to be 

conservative and to use the upper end of 

the range of birds needed for long-term 

persistence according to the model (920, 

the sum of the mean final total 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part III: Recovery Criteria and Actions. 

54

population size of 611 + the standard 

deviation of 309) as our interim target 

for recovery. We view this number of 

ducks as an absolute minimum. 

Criterion 3. There are no captive 

Laysan ducks in the State of Hawai`i. A 

new population from wild source stock, 

managed primarily for reintroduction to 

the wild, should be established. It may 

be possible to establish all new 

Northwestern Hawaiian Islands 

populations with source birds from 

Laysan, and establish Main Hawaiian 

Island populations from (new) captivehatched stock. 

Criterion 4. Human-assisted 

“immigration” (translocation of wild 

birds) is needed to offset genetic losses 

resulting from founder effects, genetic 

drift, and close inbreeding. Genetic 

drift, the cumulative and nonadaptive 

fluctuations in allele frequencies, may 

inhibit population viability. Dispersal 

between populations can slow genetic 

losses due to genetic drift and can 

augment numbers following a local 

population decline. As few as one 

migrant per generation may be sufficient 

to improve viability of the translocated 

populations (e.g., Mills and Allendorf 

1996, Wang 2004). Population viability 

analysis incorporating movement 

between populations showed greater 

persistence in those populations. 

Because of the risk of disease, the 

mixing of captive birds from the main 

islands with wild populations in the 

Northwestern Hawaiian Islands should 

be avoided, except in case of emergency 

or catastrophe to the source population. 

The risk posed by diseases introduced to 

the Northwestern Hawaiian Islands 

threatens the source population of ducks 

and other endangered bird species on 

Laysan. Wild source eggs should be 

added periodically to captive source 

populations to improve genetic diversity 

and reduce genetic drift. If wild source 

juvenile birds are added to the captive 

flock, these birds should first be treated 

for echinuriasis to prevent the 

introduction of Echinuria to other 

islands. 

Criterion 5. A comprehensive 

management plan will guide 

implementation of recovery actions for 

each population to ensure that the 

species does not become endangered 

again. Population viability models 

indicated that supplementation greatly 

improved population growth rates and 

may be required to maintain long-term 

population viability. Other management 

options to reduce or eliminate the 

current threats to the Laysan duck and 

increase population growth should be 

identified in the management plan. 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part III: Recovery Criteria and Actions. 

55

C. Outline of Recovery Actions 

1. Address risks to the Laysan duck population on Laysan Island 

 1.1. Population monitoring 

1.1.1. Population and reproductive monitoring 

1.1.2. Disease screening and prevention 

1.1.3. Field crew training 

1.2. Develop emergency contingency plans 

1.3. Further research 

1.3.1. Population parameters (including nesting success) 

1.3.2. Disease 

1.3.3. Genetics research 

1.4. Implementation of the Laysan Ecosystem Restoration Plan 

1.4.1. Plant monitoring, weed control, and native species restoration 

1.4.2. Alien invertebrate control and monitoring, and native invertebrate 

restoration, where possible 

1.4.3. Freshwater seep restoration 

2. Hire or contract project leader for Laysan duck recovery 

3. Translocations 

3.1. Complete site assessments and prioritize translocation sites 

 3.1.1. Develop management plans for individual translocation sites 

3.2. Habitat restoration/creation in Northwestern Hawaiian Islands 

3.3. Habitat restoration in Main Hawaiian Islands 

3.3.1. Control predators 

3.3.2. Control of other alien species 

3.4. Set up holding facilities 

3.5. Arrange timely transportation to and from Northwestern Hawaiian Islands 

3.6. Select and transport fledged juvenile birds on Laysan 

3.7. Disease screening and treatment 

3.8. Acclimation and soft release 

3.9. Intensive post-release monitoring 

3.9.1. Radio telemetry, foraging behavior, and prey-base monitoring 

3.9.2. Body condition assessment and supplemental feeding 

3.9.3. Monitor reproduction of translocated birds 

 3.10. Immigration translocations 

 4. Captive propagation 

4.1. Develop a captive propagation program 

4.2. Release captive-bred birds 

5. Public outreach 

5.1. Outreach for translocations in Main Hawaiian Islands 

5.2. Exhibit with captive Laysan ducks on Main Hawaiian Islands 

6. Update the recovery plan 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part III: Recovery Criteria and Actions. 

56

D. Recovery Action Narrative 

The following actions are those needed to achieve the recovery of the Laysan 

duck presented in the form of a step-down narrative. Details of the ecology and 

management techniques relevant to these actions are described in Parts I and II of this 

plan. 

1. Address risks to the Laysan duck population on Laysan Island 

 1.1. Population monitoring

Because the Laysan duck exists as a single isolated population, monitoring is 

essential for guiding the species’ management and recovery. Accurate 

population estimates are needed to monitor responses to ecosystem restoration, 

gauge the health of the population, time translocation efforts during periods of 

population increases, and determine if recovery criteria have been met. 

1.1.1. Population and reproductive monitoring 

Researchers have determined that to accurately measure population size 

a ratio of marked to unmarked birds is needed (Marshall 1992b). Bandreading and population surveys are performed every 2 weeks to provide 

data for estimates, but currently no program is in place to band birds on a 

regular basis. If the population size is to be estimated with accuracy, 

long-term banding efforts and subsequent data management for resight 

histories must be maintained. A large proportion of the population was 

marked in the years 1998 through 2001, and banding once per year by 

qualified personnel is sufficient to band an adequate percentage of 

fledglings. Population trends and recruitment must be assessed annually 

using data collected from field sites. Additional trend assessments and 

analysis should be conducted as needed. 

1.1.2. Disease screening and prevention 

Disease screening and preventive treatment are needed before Laysan 

ducks are translocated. Screening will serve to select only healthy birds 

for removal and prevent spread of disease. Collection, preservation, and 

necropsy of suitable carcasses should be continued in coordination with 

the U.S. Geological Survey National Wildlife Health Lab. Echinuria has 

not been documented in Hawai`i outside of Laysan, and translocated 

Laysan ducks could introduce the parasite to other islands. Prevention of 

botulism outbreaks and strategies for preventing the introduction of new 

diseases to the Northwestern Hawaiian Islands should be explored. 

1.1.3. Field crew training 

Conservation activities on Laysan Island depend in large part on the 

dedication of crews of technicians and volunteers that spend 4 or 5 

months on the island carrying out a range of projects. Because of 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part III: Recovery Criteria and Actions. 

57

staffing, logistical, and financial constraints, training of crews often is 

limited, and lack of continuity between crews can reduce the 

effectiveness of monitoring, restoration actions, and record keeping. 

Crews need adequate training in Laysan duck monitoring: sexing, 

ageing, and counting birds and reading bands. Additional effort is 

required for reproductive monitoring during the typical brood rearing 

season from March to August. An individual (technician or volunteer) 

devoted to collecting data for determining reproductive success is needed 

to adequately monitor the population. 

1.2. Develop emergency contingency plans 

Given the destructive potential of introduced predators and competitors, and 

the likelihood of future introductions, a contingency plan is needed to deal with 

introduced species that might find their way to Laysan or translocation sites. 

Refuge managers should be prepared for possible introductions of rats, mice, or 

ants, know what to do in the case of a hurricane, and know how to respond to 

epizootics or contaminants washing ashore. 

1.3. Further research 

Although much has been learned about the Laysan duck in the past two 

decades, further research is essential for directing and revising future recovery 

efforts. 

1.3.1. Population parameters 

More information is needed on the parameters that drive population 

dynamics on Laysan, especially those factors that influence nesting 

success, hatchability, and brood survival.

1.3.2. Disease 

Research is needed to determine how disease influences survival and 

recruitment in Laysan ducks. Parasitism rates and effects of other 

diseases are unknown. The ecology of the Echinuria parasite is 

unknown on Laysan. Research to determine the intermediate host and 

factors influencing the prevalence of echinuriasis and botulism is needed 

so epizootics can be prevented or managed (see also Action 3.3, Disease 

screening and treatment). 

1.3.3. Genetics research 

Because of their isolation and limited numbers, Laysan duck populations 

will require genetic management to prevent the loss of genetic diversity 

to random drift, founder effects, and close inbreeding. Analysis of 

heterogeneity and population structures of translocated, new captive, and 

source populations will benefit planning for species recovery. 

1.4. Implementation of the Laysan Ecosystem Restoration Plan 

Introduced species control and seep restoration are the most important 

components of the existing Laysan Ecosystem Restoration Plan (Morin and 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part III: Recovery Criteria and Actions. 

58

Conant 1998) for the recovery of the Laysan duck on that island. Without 

continued ecosystem restoration, the carrying capacity of Laysan may decline 

as freshwater seeps fill and nonnative species invade. Many of the goals set in 

the restoration plan have not yet been reached. Restoration projects are 

outlined and described in detail by Morin and Conant (1998). 

1.4.1. Plant monitoring, weed control, and native species restoration 

Continued vegetation monitoring and restoration are necessary to 

control and exterminate introduced species, restore native species that 

provide nesting and foraging habitat for the Laysan duck, and, where 

warranted, reduce sand destabilization and filling of the lake and seeps. 

1.4.2. Alien invertebrate control and monitoring, and native invertebrate 

restoration, where possible 

Native terrestrial insects are essential components of a functioning 

ecosystem as well as an important seasonal food source for the Laysan 

duck. Trained personnel should conduct regular surveys to identify and 

collect specimens, and should assess the impacts of introduced ants. 

Control requires a qualified entomologist to implement eradication 

programs and to determine which other alien invertebrates need to be 

eliminated. 

1.4.3. Freshwater seep restoration 

The freshwater seeps on Laysan are believed to be crucial brood rearing 

habitat for the Laysan ducklings. Evidence suggests that brood rearing 

habitat is limited on Laysan; seep restoration thus would improve and 

increase available habitat. During droughts on Laysan, seeps could be 

excavated so that fresh water below ground is available to birds. 

Restoration is crucial in areas where seeps or ponds existed previously or 

have been partially filled. Where wetland restoration or creation is 

warranted on Laysan Island and at other potential translocation sites, a 

hydrologist should make a site visit and assessment, and develop a 

wetland hydrology plan. Care should be taken so that water use for the 

camp and greenhouse operations on Laysan Island does not deplete fresh 

groundwater that feeds seeps during dry periods. 

2. Hire or contract project leader for Laysan duck recovery 

Dedicated staff is necessary to implement and coordinate the various aspects of 

Laysan duck recovery. Laysan Island and translocation sites need professional 

expertise in devising and implementing restoration plans, restoring and 

manipulating hydrology, translocating birds, coordinating restoration and recovery 

implementation, and monitoring. A biologist from our agency, or a contract 

scientist or group, should be dedicated to oversee implementation of this recovery 

plan. This person or group would direct the prioritization of translocation sites, 

lead fundraising efforts, and coordinate all phases of research, translocation, and 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part III: Recovery Criteria and Actions. 

59

monitoring. The project leader also would be responsible for the management and 

analysis of data generated by recovery tasks, and would develop recommendations 

for modifications to the recovery strategy in response to new information. 

3. Translocations 

Because they lack mammalian predators, the Northwestern Hawaiian Islands 

provide attractive potential translocation sites for the Laysan duck in spite of 

significant logistical hurdles. These small islands have limited carrying capacity, 

however, and to delist the Laysan duck it will be necessary to establish selfsustaining populations of Laysan ducks on the Main Hawaiian Islands as well, in 

spite of the presence of predators. Only the main islands can, with adequate 

management, support the birds in sufficient numbers to ensure their long-term 

persistence. 

3.1. Complete site assessments and prioritize translocation sites 

The development of a prioritized list of translocation sites and selection of an 

initial release site will require some additional research. The biological and 

physical assessment of potential translocation sites in the Northwestern 

Hawaiian Islands and Main Hawaiian Islands must be augmented with an 

assessment of the costs and management feasibility of habitat creation or 

restoration, translocation, and monitoring. This task will be undertaken by the 

project leader for Laysan duck recovery. 

3.1.1. Develop management plans for individual translocation sites 

Laysan ducks will benefit from the development of restoration and 

management plans for individual islands and sites. Ecosystem restoration 

will provide the best environment for self-sustaining, low-maintenance 

Laysan duck populations. 

3.2. Habitat restoration/creation in the Northwestern Hawaiian Islands 

At this time, only the Northwestern Hawaiian Islands lack mammalian 

predators, but most of those small islands will require habitat restoration to 

support the establishment of self-sustaining, minimally managed Laysan duck 

populations. We predict that the most intact native ecosystems will be the most 

likely to have adequate nesting cover, food resources, and fresh water. At such 

sites, additional management to promote the survival of translocated Laysan 

ducks will be minimal (see Appendix 2 for an island-by-island assessment). 

Many of the Northwestern Hawaiian Islands lack standing fresh water, thus 

seeps, ponds, or artificial watering devices must be created and maintained to 

ensure the survival and reproduction of translocated Laysan ducks. The 

Northwestern Hawaiian Islands harbor many introduced species of plants and 

animals, which may affect habitat quality for the Laysan duck. Control or 

eradication of these species and strict quarantine to prevent new introductions 

will improve the habitat and increase the likelihood of establishing a healthy, 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part III: Recovery Criteria and Actions. 

60

low-maintenance population. Degraded systems may require more intensive 

management to ensure Laysan duck survival, such as supplemental feeding, 

watering, and the creation of nesting cover (an example of intensive 

management for Laysan ducks is protection of hatching eggs from introduced 

fire ants using site-specific treatments at wild nests). 

3.3. Habitat restoration in the Main Hawaiian Islands 

3.3.1. Control predators 

Introduced mammalian predators probably were responsible for the 

disappearance of Laysan ducks from the Main Hawaiian Islands in 

prehistory. The most important aspect of management on the main 

islands will be control of predators. Rats, mongooses, pigs, dogs, mice, 

and feral cats are present in some combination on all of the Main 

Hawaiian Islands. All of these mammals pose a threat to the Laysan 

duck, and the presence of any predators at translocation sites would 

greatly increase the risks associated with reintroduction. Before Laysan 

duck populations can be established on any of these islands, long-term 

predator control and/or predator-proof fencing is necessary. 

3.3.2. Control other alien species 

Translocation sites may need rehabilitation in the form of introduced 

weed or insect control (refer to Appendix 2 for a site-by-site evaluation 

of possible translocation sites and restoration needs at each site). Control 

of feral mallards, which hybridize with koloa ducks, may also reduce 

potential hybridization risks to the Laysan duck. Additional 

experimental translocations in the Main Hawaiian Islands should be 

attempted where overlap with the koloa is minimal and mallards are 

absent. 

3.4. Set up holding facilities 

Individual holding and transport cages are needed to contain birds on 

Laysan and in transit. Translocated fledgling birds should be held in aviary 

facilities at new sites prior to release. While the wild birds are held in the 

aviary facility, they can be acclimated to supplemental foods and their health 

and body condition enhanced before release. 

3.5. Arrange timely transportation to and from the Northwestern Hawaiian 

Islands 

Space on ships and transportation to the Northwestern Hawaiian Islands is 

extremely limited. These logistical constraints must be addressed or they could 

hamper the implementation of most aspects of the recovery plan. 

3.6. Collect and transport fledged juvenile birds on Laysan 

Reproductive success on Laysan varies considerably from year to year, so 

translocations may have to be spaced out over a number of years. Fledged 

juveniles are the best candidates for the initial translocations because the 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part III: Recovery Criteria and Actions. 

61

removal of juvenile birds has the least impact on the source population. After 

translocated birds begin breeding, experimental techniques for supplementation 

or cross-fostering with younger ducklings or eggs harvested from Laysan 

should be explored if necessary. The removal of birds from Laysan must be 

timed according to population trends. Birds should be transferred in multiple 

years, 15 to 30 fledglings per year for the first 2 years, if enough suitable 

individuals exist. Immigrants should be added regularly thereafter from the 

source population. Fledglings could be selected and removed between July and 

October. 

3.7. Disease screening and treatment 

It is especially important to screen and treat birds prior to translocation to 

avoid transferring disease to transfer populations or translocation sites. 

Ivermectin is an anti-parasite medication known to eliminate roundworms, but 

the response of Laysan ducks to this drug is not known. If the risk to the 

ducks’ health is deemed insignificant, safety trials should be conducted on 

captive Laysan ducks before ivermectin is widely administered to birds that 

will be translocated. It is also important to evaluate the disease risk at new 

sites prior to translocation. 

3.8. Acclimation and soft release 

Laysan ducks must be acclimated to translocation sites prior to release to 

ensure that birds are healthy and are able and inclined to forage in their new 

environment. Birds will be housed in aviary pens at the release site and 

monitored for several weeks until they regain their pre-capture condition. 

During this period, the ducks will be closely monitored and offered a 

combination of wild forage items and supplements. Once the majority of birds 

appear healthy, those in good condition will be prepared for release. Ideally, 

release will occur after birds have reached their pre-translocation weights, and 

are deemed in good body condition. Those not adapting to aviary life may be 

released prior to reaching their pre-translocation weights if deemed necessary. 

Radio transmitters will be re-attached so that post-release activity can be 

monitored immediately. Primary feathers will be trimmed to prevent flight 

dispersal from the release site. Birds will be released with their aviary mates, 

and a first group will be monitored for 2 to 3 days prior to releasing the next 

group. Supplemental food and water will be offered for up to 2 months post 

release at the release site to give the ducks time to explore their new foraging 

habitat. 

3.9. Intensive post-release monitoring 

To determine the efficacy of the release program, the fates of translocated birds 

must be followed closely. Findings will enable managers to adapt the 

translocation program during its development. 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part III: Recovery Criteria and Actions. 

62

3.9.1. Radio telemetry, foraging behavior, and prey-base monitoring 

Radio telemetry is the most effective means of tracking individual birds 

and monitoring their activity and reproductive effort. Because the 

Laysan duck has been studied only on Laysan, knowledge of their 

foraging behavior in other environments is unknown. Monitoring the 

prey base of the ducks at translocation sites will enable managers to 

determine seasonal availability of food, preferred foraging habitats, and 

whether supplemental feeding is warranted. 

3.9.2. Body condition assessment and supplemental feeding 

Body condition should be used as an indicator of health and adequate 

food resources. Birds in poor condition may require treatment and 

conditioning in an on-site aviary, and may serve as indicators that 

improvements to the habitat quality at the release site are needed. 

Supplemental food and water should be offered after release and during 

periods of low seasonal availability as determined by prey base and postrelease monitoring. Individuals in poor condition may require 

supplemental feeding. 

3.9.3 Monitor survivorship and reproduction of translocated birds 

Translocated birds should be monitored for at least 2 years post-release 

to ensure the success of the translocation program and allow for 

adjustments in the protocol, if necessary. Data gathered on survivorship 

and reproduction of birds in these new environments will be critical in 

the assessment of population viability and for the development of 

scientifically sound delisting criteria for this species. 

3.10 Immigration translocations 

After the initial translocation, one bird per generation (or five birds every 5 

years) should be transferred from Laysan to the newly established populations 

on other islands. Additional supplementation may be required to increase 

population growth. Immigration between the Northwestern Hawaiian Islands 

populations should continue over the long term because none of these islands 

will be able to support a very large population of Laysan ducks. Continued 

immigration thus is an important part of the project to reduce the effects of 

inbreeding and genetic drift. 

4. Captive propagation 

The existing captive flocks of Laysan ducks on the mainland and in international 

facilities are unsuitable for introduction to the wild. A new captive population, 

managed specifically for establishing additional wild populations, is needed in the 

Main Hawaiian Islands. Removal of eggs from Laysan would have the least 

impact on the source population. Removal and transport of eggs to the main 

islands may also be easier logistically. While preparations are made for captive 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part III: Recovery Criteria and Actions. 

63

propagation, wild-source fledgling individuals may be translocated to suitable 

habitats on other islands to establish insurance populations. 

4.1. Develop a captive propagation program 

Captive propagation for Laysan ducks, including planning, facility 

development, and staffing, should be pursued through contracts with non-profit 

organizations. 

4.2. Release captive-bred birds 

Similar to wild translocated birds, Laysan ducks raised in captivity will need 

disease screening prior to release and close monitoring afterward. 

5. Public outreach 

5.1. Outreach for translocations in the Main Hawaiian Islands 

Any translocation effort on an inhabited island should include a public outreach 

program. Those responsible for implementing recovery actions on the islands 

should advertise the goals and objectives of the translocation, solicit responses, 

and address stakeholder concerns, ideally prior to the translocation. 

5.2. Exhibit with captive Laysan ducks 

An interpretive exhibit (e.g., at the Honolulu Zoo, Waikiki Aquarium, or 

Sealife Park) should be developed using some of the existing captive Laysan 

ducks from mainland captive stock, or nonbreeders from new captive flocks. 

Such an exhibit could provide information about the duck’s status (updated as 

translocations and recovery progress) and about the Northwestern Hawaiian 

Islands in general. 

6. Update the recovery plan 

The recovery plan for the Laysan Duck should be reviewed and updated 

periodically, as necessary, as research and translocations progress and we gain 

further knowledge of the ecology and population biology of the Laysan duck in 

new environments. The need for data necessary to develop defensible delisting 

criteria for this species is recognized as a high priority. Although revision may 

occur earlier, if appropriate, this plan should be revised within 5 years, since 

the actions and cost estimates presented in the implementation schedule are 

currently for only a 5-year timeframe due to the numerous uncertainties 

associated with this species.
Laysan Duck Draft Revised Recovery Plan, August 2004. Part IV: Schedule 2004-2008. 

64

IV. IMPLEMENTATION SCHEDULE FOR 2004 TO 2008 

Although we now know that the 

Laysan duck once occurred throughout 

the Hawaiian islands and lived in a 

broad range of habitats, our 

understanding of this bird’s ecology is 

limited to our observations of the single 

remnant population that occurs in a 

relatively unusual habitat dominated by 

a hypersaline lake. Because we don’t 

know how well our current knowledge 

of Laysan duck biology may apply to 

the management of this species in other 

habitats, long-term planning for its 

reestablishment and recovery is difficult. 

The needs of the recovery program thus 

cannot realistically be projected beyond 

a relatively limited timeframe. As a 

consequence, we take an adaptive 

management approach to the recovery of 

the Laysan duck to permit the 

refinement of recovery actions as we 

learn more about the needs of this 

species through the recovery process. 

This implementation plan outlines the 

actions needed to advance the recovery 

program for the Laysan duck over the 

next 5 years; new implementation plans 

will be prepared every 3 to 5 years to 

reflect the lessons learned and 

refinements to our management strategy. 

In this way, we will review and enhance 

the effectiveness of the Laysan duck 

recovery program. 

The Implementation Schedule that 

follows outlines actions and estimated 

costs for the Laysan duck recovery 

program as set forth in this recovery 

plan. It is a guide for meeting the 

objectives discussed in Parts II and III of 

this plan. This schedule indicates action 

priority numbers (defined below), action 

numbers from the recovery action 

outline in Part III-A, action descriptions, 

anticipated duration of actions, the 

responsible parties, and lastly, estimated 

costs. The initiation and completion of 

these actions is subject to the 

availability of funds, as well as other 

constraints affecting the parties 

involved. 

We have the statutory responsibility 

for implementing this recovery plan, and 

only Federal agencies are mandated to 

take part in recovery efforts for 

threatened and endangered species. 

However, recovery of the Laysan duck 

will require the involvement of the full 

range of Federal, State, private, and 

local interests. The expertise and 

contributions of additional agencies and 

interested parties is needed to implement 

certain recovery actions and to 

accomplish outreach objectives. For 

each recovery action described in the 

Implementation Schedule, the column 

titled “Responsible Parties” lists the 

primary agencies having the authority or 

responsibility for implementing 

recovery actions and other groups, such 

as state, private, and non-profit 

organizations, that also may wish to be 

involved in recovery implementation. 

The listing of a party in the 

implementation schedule does not 

require, nor imply a requirement, that 

the identified party has agreed to 
Laysan Duck Draft Revised Recovery Plan, August 2004. Part IV: Schedule 2004-2008. 

65

implement the action(s) or to secure 

funding for implementing the action(s). 

When more than one party is listed, the 

most logical lead agency (based on 

authorities, mandates, and capabilities), 

has been identified in bold type. 

Definition of Action Priorities: 

Priority 1 — An action that must be 

taken to prevent extinction or prevent 

the species from declining irreversibly 

in the foreseeable future. 

Priority 2 — An action that must be 

taken to prevent a significant decline in 

species population or habitat quality, or 

some other significant negative impact 

short of extinction. 

Priority 3 — All other actions necessary 

to meet the recovery objectives. 

Definition of Action Durations:

Continual (C) — An action that will be 

implemented on a routine basis once 

begun. 

Ongoing (O) — An action that is 

currently being implemented and will 

continue until no longer necessary. 

To Be Determined (TBD) — The action 

duration is not known at this time or 

implementation of the action is 

dependent on the outcome of other 

recovery actions. 

Time projections for recovery are 

based on the assumption that habitat 

restoration work will begin in fiscal year 

(FY) 2004, the first translocation will 

take place in September 2004, and 

subsequent soft releases will begin in 

the spring of 2005 (depending on the 

progress of habitat restoration). The 

second translocation and release to the 

initial site will take place between 2005 

and 2006. Undertaking translocation 

efforts depends on a healthy, increasing 

population on Laysan. We estimate that 

between 15 and 20 hatch-year birds can 

be removed from the Laysan population 

during increasing or stable years. 

Acronyms used in the Implementation Schedule: 

BRD U.S. Geological Survey-Biological Resources Division 

DLNR Hawai`i Division of Land and Natural Resources 

DU Ducks Unlimited, Inc. 

HINWR Hawaiian Island National Wildlife Refuge 

KIRC Kaho`olawe Island Reserve Commission 

MHI Main Hawaiian Islands 

NWHI Northwest Hawaiian Islands 

NWHRC National Wildlife Health Research Center 

PL Project leader for Laysan duck recovery, affiliation to be determined 

USFWS U.S. Fish and Wildlife Service 

WRD U.S. Geological Survey-Water Resources Division 
Table 3. Implementation Schedule for the Laysan duck draft revised recovery plan. 

Recovery Estimated 

Action 

Priority 

Action 

Number 

Listing 

Factor 

Action Description Action 

Duration 

Responsible Parties 

Total 

Cost 

FY 

2004 

F

2

1 1.1.1 A, E Population and reproductive monitoring O USFWS/BRD 200 40 1 1.1.2 C Disease screening and prevention C USFWS/NWHRC 22 6 1 1.2 E Develop emergency contingency plans TBD USFWS/PL/private 

contractor 

35.5 35.5 

1 2 A, C, E Hire or contract project leader for Laysan duck 

recovery (PL) 

C USFWS/BRD/ 

private contractor 

3,315 66.3 6

1 3.1 A, E Complete site assessment and prioritize 

translocation sites 

C USFWS/PL 37 37 

1 3.2 A, E Restore and/or create habitats on NWHI that 

are potential translocation sites (e.g., Eastern Island at Midway Atoll) 

C USFWS/DLNR/ 

DU/other private 

contractor 

3,500 840 8

1 3.3.1 C Control predators at potential MHI 

translocation sites (e.g., Kaho`olawe, Hanalei NWR, Kaua`i) 

C USFWS/DLNR/ 

KIRC 

750 150 1

2 1.1.3 E Train Laysan field crews in survey methods O USFWS 27 5.4 

66
Table 3. Implementation Schedule for the Laysan duck draft revised recovery plan. 

Recovery Estimated 

Action 

Priority 

Action 

Number 

Listing 

Factor 

Action Description Action 

Duration 

Responsible Parties 

Total 

Cost 

FY 

2004 

F

2

2 1.3 C, E Conduct research on Laysan duck population 

parameters, genetics, and disease susceptibility 

O USFWS/research 

institutions

300 60 

2 1.4.1 A Control and monitor weeds and restore native 

vegetation on Laysan 

O USFWS 1,000 200 2

2 1.4.3 A Restore seeps on Laysan C USFWS/DU/WRD 250 75 2 3.9.2 E Conduct body condition assessment and 

supplemental feeding of translocated ducks 

TBD USFWS/BRD/ 

research institutions 

140 

2 4.1 A, E Develop captive propagation program, incl. 

planning, facility development, and staff 

C Private contractor 490 130 

3 1.4.2 A, E Control and monitor invasive invertebrates 

and restore natives on Laysan 

C USFWS 375 75 

3 3.1.1 A, E Develop management plans for individual 

translocation sites 

C USFWS/PL/BRD 90 

3 3.3.2 A, E Control alien species (e.g., weedy plants, feral 

mallards) at MHI translocation sites 

C USFWS/DLNR/ 

KIRC

432 144 

67
Table 3. Implementation Schedule for the Laysan duck draft revised recovery plan. 

Recovery Estimated 

Action 

Priority 

Action 

Number 

Listing 

Factor 

Action Description Action 

Duration 

Responsible Parties 

Total 

Cost 

FY 

2004 

F

2

3 3.4 A, E Set up holding 

facilities 

TBD USFWS/BRD/ 

private contractor 

75 

3 3.5 A, E Charter transportation to and from HINWR TBD USFWS 350 70 3 3.6 A, E Capture fledged juvenile birds on Laysan TBD USFWS/BRD 80 3 3.7 C Disease screening and treatment TBD NWHRC 40 3 3.8 A, C, E Acclimation and soft release TBD USFWS/BRD 280 3 3.9, 

3.9.1, 

3.9.3 

A, C, E Conduct intensive post-release monitoring of 

translocated ducks: radio tracking, foraging behavior, prey-base 

TBD USFWS/BRD/ 

research institutions 

140 

3 3.10 E Conduct immigration translocations to 

maintain genetic variability in new duck populations 

TBD USFWS/BRD/ 

research institutions 

45 

3 4.2 A, E Release captive-bred Laysan ducks (includes 

intensive post-release monitoring) at MHI sites (e.g., Kaho’olawe and Kaua’i) 

TBD USFWS/BRD/ 

research institutions 

105 

68
Table 3. Implementation Schedule for the Laysan duck draft revised recovery plan. 

Recovery Estimated 

Action 

Priority 

Action 

Number 

Listing 

Factor 

Action Description Action 

Duration 

Responsible Parties 

Total 

Cost 

FY 

2004 

F

2

3 5.1 A, E Conduct public outreach for reintroduction of 

Laysan ducks to MHI 

C USFWS/DLNR 75 15 

3 5.2 A, E Create interpretive exhibit using captive 

Laysan ducks 

C Private contractor 150 45 

3 6 A, C, E Update recovery plan 1 year USFWS 5 

TOTALS 9,325 1,994 2

69 
Laysan Duck Draft Revised Recovery Plan, August 2004. 

70

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9:182-195. 

Temple, S. A. 1985. Why endemic island birds are so vulnerable to extinction. Pages 3-

6 in S. A. Temple and Jerome Jackson, eds. Bird Conservation 2. University of 

Wisconsin Press, Madison, WI. 180 pp. 

Towns, D. R., D. Simberloff, and I. A. E. Atkinson. 1997. Restoration of New Zealand 

islands: redressing the effects of introduced species. Pacific Conservation Biology 

3:99-124. 

Townsend, C. R., J. L. Harper, and M. Begon. 2000. Essentials of ecology. Blackwell 

Science, Inc., Malden, MA. 552 pp. 

USFWS (U.S. Fish and Wildlife Service). 1967. Endangered Species List - 1967. 

Federal Register 32:4001. 

USFWS (U.S. Fish and Wildlife Service). 1982. The Laysan duck recovery plan. U.S. 

Fish Wildlife Service, Portland, OR. 38 pp. 

USFWS (U.S. Fish and Wildlife Service). 1983a. Endangered and Threatened Species 

Listing and Recovery Priority Guidance. Federal Register 48:43098-43105. 

USFWS (U.S. Fish and Wildlife Service). 1983b. Endangered and Threatened Species 

Listing and Recovery Priority Guidelines Correction. Federal Register 48:51985. 
Laysan Duck Draft Revised Recovery Plan, August 2004. 

81

USFWS (U.S. Fish and Wildlife Service). 1987. Field guide to wildlife diseases. U.S. 

Department of the Interior, Washington, D.C. 

USFWS (U.S. Fish and Wildlife Service). 2001. Standard Operating Procedure - Laysan 

Island. U.S. Fish and Wildlife Service, Honolulu, HI. 

USFWS (U.S. Fish and Wildlife Service). 2002. Endangered Species Bulletin. 

March/June 2002. Vol. XXVII, No. 2. Washington, D.C. 

van Riper, C., and S. G. van Riper. 1985. A summary of known parasites and diseases 

recorded from avifauna of the Hawaiian Islands. Pages 298-371 in C. P. Stone and J. 

M. Scott, eds. Hawai`i's terrestrial ecosystems preservation and management. 

Proceedings of a symposium held June 5-6, 1984 at Hawai`i Volcanoes National 

Park. University of Hawai`i Press, Honolulu, HI. 616 pp. 

Veitch, C. R. 1995. Habitat repair: a necessary prerequisite to translocation of 

threatened birds. Pages. 97-104 in M. Serena, ed. Reintroduction biology of 

Australian and New Zealand fauna. Surrey Beatty and Sons, Chipping Norton, New 

South Wales, New Zealand. 

Wang, J. 2004. Application of the one-migrant-per-generation rule to conservation and 

management. Conservation Biology 18:332-343. 

Warner, R. E. 1963. Recent history and ecology of the Laysan duck. Condor 65:3-23. 

Warner, R. E. 1968. The role of introduced diseases in the extinction of the endemic 

Hawaiian avifauna. Condor 70:101-120. 

Weller, M.W. 1980. The island waterfowl. Iowa State University Press, Ames, IA. 121 

pp. 

Wetmore, A. 1925. Bird life among lava rock and coral sand. National Geographic 

Magazine 48:76-108. In Ely, C. A., and R. B. Clapp. 1973. The natural history of 

Laysan Island, Northwestern Hawaiian Islands. Smithsonian Institution, 

Washington, D.C. 

Wiggins, J. W., D. Carroll, and A. Wegmann. 2001. Trip Report: Laysan Island, 19 

February 2001 to 10 August 2001. U.S. Fish and Wildlife Service, Honolulu, HI. 
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82

Williams, M.J. 1974. Creching behaviour of the shelduck Tadorna tadorna. L. Ornis 

Scandinavica 5:131-143. In Batt, B.D., A.D. Afton, M. G. Anderson, C.D. Ankney, 

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breeding waterfowl. University of Minnesota, Minneapolis, MN. 635 pp. 

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Wobeser, G., and J. Howard. 1987. Mortality of waterfowl on a hypersaline wetland as a 

result of salt encrustation. Journal of Wildlife Diseases 23:127-134. 

B. Personal Communications 

Becker, Brenda. National Marine Fisheries Service, Honolulu, HI. 

Berry, Matt. U.S. Fish and Wildlife Service, Pacific/ Remote Islands National Wildlife 

Refuge Complex, Honolulu, HI. 

Engilis, Andrew J. Museum of Wildlife and Fish Biology, University of California at 

Davis, Davis, CA. 

Flint, Elizabeth N. U.S. Fish and Wildlife Service, Pacific/Remote Islands National 

Wildlife Refuge Complex, Honolulu, HI. 

James, Helen. Smithsonian Institution Museum of Natural History, Washington, D.C. 

Kuehler, Cindy. Keahou Bird Conservation Center, Volcano, HI. 

Marshall, Ann. U.S. Fish and Wildlife Service, Pacific Islands Fish and Wildlife Office, 

Honolulu, HI. 

Reilly, Sharon. Ducks Unlimited, Honolulu, HI. 

Reynolds, Michelle. U.S. Geological Survey, Biological Resources Division, Kilauea 

Field Station, Hawai`i Volcanoes National Park, HI. 

Swenson, Chris. U.S. Fish and Wildlife Service, Pacific Islands Fish and Wildlife Office, 

Honolulu, HI. 

Woodward, Lee Ann. U.S. Fish and Wildlife Service, Pacific/Remote Islands National 

Wildlife Refuge Complex, Honolulu, HI. 

Work, Thierry. U.S. Geological Survey, National Wildlife Health Research Center, 

Honolulu, HI. 
Laysan Duck Draft Revised Recovery Plan, August 2004. Appendix 1. 

83

VI. APPENDICES 

Appendix 1. Habitat assessments of possible translocation sites for the Laysan 

duck. 

I: Northwestern Hawaiian Islands 

Island 

Size 

(ha) 

Elevation 

(m) 

Annual 

rainfall

(mm) 

Surface 

fresh water Cover Predators 

Prey 

base 

Kure Atoll 100 6 1100 Absent Yes Absent Moderate 

Midway Atoll 625 5 1121 - Yes Absent Moderate 

 Sand Is. 467 5 Limited Limited Absent Moderate 

 Eastern Is. 156 4 Absent Limited Absent Moderate 

 Spit Is. 2 2 Absent Limited Absent Limited 

Pearl and 

Hermes 

30 3 700-

1000 

Absent No Absent Limited 

 South East Is. 2 Absent No Absent Limited 

 North Is. 3 Absent Yes Absent Limited 

 Kittery Is. 2 Absent No Absent Limited 

Lisianski 150 11 700-

1000 

Absent Yes Absent Moderate 

Laysan 415 12 700-

1000 

LimitedModerate Yes Absent Seasonally 

abundant 

French Frigate 

Shoal 

26 1-3 700-

1000 

Absent No Absent Limited 

Tern 10 Absent No Absent Limited 

Necker 18 83 500 -

750 

Limited No Absent Unknown 

Nihoa 68 269 750 Moderate Yes Absent Moderate 
Laysan Duck Draft Revised Recovery Plan, August 2004. Appendix 1. 

84

Appendix 1 (continued). Habitat assessments of possible translocation sites. 

II: Main Hawaiian Islands. 

Island 

Size 

(ha) 

Maximum 

Elevation 

(m) Site 

Annual 

rainfall 

(mm) 

Surface 

fresh 

water Predators 

Ni`ihau 25,500 390 Ni’ihau Playas 667 Abundant Dogs, Cats, 

Rats 

Kaua’i 157,400 1,585 Wainiha Valley 

Lumaha’i Valley 

Hanalei NWR 

Wailua/Opaekaa Valley 

Hule’ia NWR 

National Tropical Botanical 

Garden 

(Lawa’i Valley) 

2000 

2500 

2000 

1250 

1250 

---- 

Abundant Dogs, Cats, 

Rats 

Oahu 162,400 1,233 Lualualei 

‘Uko’a Marsh 

Kahuku Point 

La’ie Wetlands 

Waihe’e Marsh 

He’eia Marsh 

Nu’upia Ponds 

Kawai Nui Marsh 

625 

500 

1250 

1500 

2000 

1750 

1250 

1500 

Abundant Dogs, Cats, 

Rats, 

Mongooses 

Moloka’i 66,600 1,525 Moloka’i Playas 

Kaunakakai Wetlands 

Kakahai’a NWR 

Paialoa Pond 

250 

375 

625 

750 

Abundant Dogs, Cats, 

Rats, 

Mongooses 

Lana’i 35,500 1,437 Whole island 250-500 Abundant Dogs, Cats, 

Rats 

Kaho`olawe 12,100 450 Whole island 250-500 Limited Cats 
Laysan Duck Draft Revised Recovery Plan, August 2004. Appendix 1. 

85

Island 

Size 

(ha) 

Maximum 

Elevation 

(m) Site 

Annual 

rainfall 

(mm) 

Surface 

fresh 

water Predators 

Maui 182,700 3,050 Kanaha Pond Sanctuary 

Kealia Pond NWR 

Koanae Point 

Nu’u Pond 

500 

375 

2000 

1500 

Abundant Dogs, Cats, 

Rats, 

Mongooses 

Hawai’i 1,045,800 4,150 Pololu Valley 

Waimanu Valley 

Waipi’o Valley 

Loko Waka Ponds 

Ke’anae Pond 

Koloko Pond 

‘Opae’ula Pond 

‘Aimakapa Pond 

Kona Refuge 

1875 

2000 

2000 

3000 

3000 

250 

250 

250 

--- 

Abundant 

Limited 

Dogs, Cats, 

Rats, 

Mongooses 

 
Appendix 2-A. Assets of preferred sites evaluated for proposed reintroduction of the Lays

Assets 

Kure (Green Island) 

Midway (Eastern and Spit Islands) Lisianski Nihoa Kaho’olawe 

Kaua’i (Hanalei) 

Size of habitat Small Moderate Moderate Small Large Large Fresh water Limited; 

creation feasible 

Limited; creation feasible 

Limited; restoration feasible 

Available Limited; 

ephemeral wetlands and gulches present; wetland enhancement proposed 

Abundant 

Nesting cover Moderate Low, but 

restoration ongoing 

Excellent Good Moderate with 

restoration ongoing 

Good 

Predicted food abundance 

Moderate Moderate to high Moderate Good Moderate Abundant 

86 
Appendix 2-A (continued). Assets of preferred sites evaluated for proposed reintroduction of the 

Assets 

Kure (Green Island) 

Midway (Eastern and Spit Islands) Lisianski Nihoa Kaho’olawe 

Kaua’i (Hanalei) N

Logistical feasibility 

Limited High Moderate Difficult Moderate High D

Plant foods Low Moderate Moderate Moderate Low Abundant UInfrastructure Some Good None None Some Good SLand Management* 

DLNR Wildlife Reserve 

USFWS Wildlife Refuge and Historical Site 

USFWS Wildlife Refuge 

USFWS Wildlife Refuge 

KIRC Cultural and Ecological 

USFWS Wildlife Refuge 

ProwR

*DLNR = Department of Land and Natural Resources; USFWS = U.S. Fish and Wildlife Service; KIRC = Kaho’olawe IslaCommittee

87
Appendix 2 –B. Liabilities of preferred sites evaluated for proposed reintroduction of the Lay

Liabilities 

Kure (Green Island) 

Midway (Sand, Eastern and Spit Islands) Lisianski Nihoa Kaho’olawe 

Kaua’i (Hanalei) N

Human disturbance or hazards 

 Minimal Minimal on 

Eastern & Spit; moderate on Sand 

Minimal None Minimal, after 

ordnance removal 

Moderate U

Food competitors (mice, predatory alien insects) 

High Low-moderate Low Lowmoderate Low- moderate Moderate u

Disease Low? Low? Low? Low? Low? Low? UPredators No No No No Yes Yes YManagementRequired 

Freshwater source 

1) Revegetation 2) Freshwater source 

Freshwater source 

None Predator 

removal 

Predator removal 

Pr

Management Beneficial

Weed and ant control 

Weed, ant, mouse control 

Weed and ant control 

Unknown Wetland 

restoration, mouse control 

Upland vegetation restoration 

Uvr

88 
Laysan Duck Draft Revised Recovery Plan, August 2004. Appendix 3. 

89

Appendix 3. VORTEX population viability analyses: parameters 

and conditions used and summary of results. 

I. Life history parameters used to run VORTEX population simulations for 

100 years for Laysan duck viability (Version 8.41, Lacy 1993). 

Non-territorial (Moulton and Weller 1984) 

Monogamous breeding system (Moulton and Marshall 1996) 

Breeding age: 2 years (MHR/USGS 1998-2000 data) 

Maximum breeding age: 10 (assumption) 

Clutch size: 3 to 4 (mean 3.8) (Moulton and Marshall 1996) 

Maximum brood size: 6 (MHR/USGS 1998-2000 data) 

25% (SD 12.5) of females produce ducklings each year at carrying capacity (Moulton 

 and Marshall 1996) 

50% of females produce ducklings for populations below carrying capacity1

 

Of breeding females (MHR/USGS 1998-2000 data), 

• 21% produce broods of 1 duckling 

• 23.5% produce 2 ducklings 

• 22% produce 3 ducklings 

• 13.5% produce four ducklings 

• 11% produce 5 ducklings, and 

• 9% produce 6 ducklings 

Duckling broods per year: 1 (Moulton and Marshall 1996) 

Sex ratio at birth1

: 1:1 

Mortality: 70% for both sexes between ages 0 and fledging 

 2% mortality for both sexes from fledging to 1 year 

 1% adult mortality (MHR/USGS 1998-2000 data) 

Habitat: On Laysan 267 hectares are used for foraging and nesting (Marshall 1992) (We 

assumed that with management 75% of the area of other NW Hawaiian Islands contain 

suitable habitat, except Sand Island, for which we assumed 50% suitable habitat because 

of human structures and habitat conversion); carrying capacity estimates are based on 1 

bird per 0.5 hectare vegetated habitat (Warner 1963). 

Carrying capacity of Laysan is 500 (Moulton and Marshall 1996). 
Laysan Duck Draft Revised Recovery Plan, August 2004. Appendix 3. 

90

II. Conditions for VORTEX simulations for Laysan duck viability. One hundred 

iterations were run for 100 years. 

Parameters

5 populations modeled 

No inbreeding depression 

All males in breeding pool 

Density dependent reproduction 

Both males and females disperse (via translocation) 

Rate of dispersal: 1% of population per generation 

Minimum age at dispersal: 1 (hatch-year [HY]) 

Maximum age at dispersal: 2 

Percent surviving during dispersal (translocation): 95 

Initial population size of Laysan: 475 

No Laysan supplementation or management to increase population growth 

Stable age distribution for Laysan only 

Northwestern Hawaiian Islands (NWHI) simulation only:

Correlation between environmental variation and reproduction: 0.7 

Translocation dispersal = 1% per generation for all islands 

Four catastrophes in NW Hawaiian Islands model (1.0 = no effect; 0 = total loss): 

• Severe drought and disease: 4/100 years, 0 effect on reproduction, 0.5 on survival 

• Hurricanes: 1/100 years, 0.5 effect on reproduction, 0.75 on survival 

• Anthropomorphic or unknown disaster: 2/100 years, 0.5 effect on reproduction, 

0.5 on survival 

• ENSO events: 17/100 years, 0.0 effect on reproduction, 1.0 on survival 

All catastrophes were local 

Carrying capacity (~ 1 bird per 0.5 ha. of suitable habitat; based on Laysan estimate 

(Warner 1963): 

• Laysan: 500 

• Eastern and Sand Islands, Midway Atoll: 446 

• Lisianski: 225 

• Kure: 150 

• Nihoa: 102 

• Environmental variation in carrying capacity 30% 
Laysan Duck Draft Revised Recovery Plan, August 2004. Appendix 3. 

91

Main and Northwestern Hawaiian Island Simulation: 

Correlation between environmental variation and reproduction: 0.5 

Translocation dispersal: 1% per generation for all NWHI; none from Main Islands to 

NWHI 

Four catastrophes in the main Hawaiian Islands model (1.0 = no effect; 0 = total loss): 

• Severe drought and disease: 4/100 years, .5 effect on reproduction, .75 on survival 

• Hurricanes: 1/100 years, 0.5 effect on reproduction, .5 on survival 

• Anthropogenic or unknown disaster: 2/100 years, 0.5 effect on reproduction, 0.5 

on survival 

• ENSO events: 17/100 years, 0.5 effect on reproduction, 1 on survival 

All catastrophes were local 

Harvests from Laysan are every 2 years for 17 years: 15 hatch year (HY) birds per year 

Initial population size for 2 new populations = 40 all HY captive-born birds 

Supplementation of new main island populations also from captive source: 

Kaho’olawe: 10 HY per year for 17 years 

“Main Island Predator Exclosure”: 10 HY every 2 years for 17 years 

Carrying capacity 

• Kaho’olawe : 800 

• Predator exclosure on Main Island: 500 

Environmental variation in carrying capacity 30% 

III. Results summary VORTEX simulations for Laysan duck viability. 

Northwestern Hawaiian Islands only:

Laysan population (assumes no supplementation, no other management to offset 20 years 

of harvests for translocation purposes) 

 Year 50 Probability of survival 0.76 

 Year 100 Probability of survival 0.57 (0.05 SE) 

Mean time to first extinction 38.71 years (3.40 SE) 

Midway populations (assumes 3 to 4 supplementations over 20 years) 

Year 50 Probability of survival 0.98 

Year 100 Probability of survival 0.66 (0.04 SE) 

Mean time to first extinction 70.4 years (3.26 SE) 
Laysan Duck Draft Revised Recovery Plan, August 2004. Appendix 3. 

92

Lisianski populations (assumes 3 to 4 supplementations over 20 years)) 

Year 50 Probability of survival 0.89 

Year 100 Probability of survival 0.63 (0.04 SE) 

Mean time to first extinction 61.24 years (3.57 SE) 

Kure population (assumes 3 to 4 supplementations over 20 years) 

Year 50 Probability of survival 0.93 

Year 100 Probability of survival 0.61 (0.04 SE) 

Mean time to first extinction 69.45 years (2.90 SE) 

Nihoa population (assumes 3 to 4 supplementations over 20 years) 

Year 50 Probability of survival 0.96 

Year 100 Probability of survival 0.63 (0.04 SE) 

Mean time to first extinction 61.22 years (3.26 SE) 

Northwestern Hawaiian Islands Metapopulation 

Year 50 Probability of survival 1.0 

Year 100 Probability of survival 0.94 (0.02 SE) 

Mean time to first extinction 89.17 years (3.04 SE) 

Within population means 

Year 50 Probability of survival 0.90; number of extant populations 4.52 (0.70 SE) 

Year 100 Probability of survival 0.62 (0.02 SE) 

Mean time to first extinction 61.2 years (21.26 SE) 

Years with harvest and supplementation mean growth rate (r) = 0.1796 (0.3123 SE) 

Years without harvest or supplementation r = -0.0136 (0.2743 SE) 

Across all years mean r = -0.01 (0.2843 SE) 

All populations in decline at year 50; additional supplementation and adaptive 

management needed to increase populations to carrying capacity after catastrophes. 
Laysan Duck Draft Revised Recovery Plan, August 2004. Appendix 3. 

93

Northwestern Hawaiian Islands and Main Islands:

Laysan population (immigration between NWHI only, no supplementation) 

Year 50 Probability of survival 0.86 

Year 100 Probability of survival 0.57 (0.04 SE) 

Mean time to first extinction 54. 77 years (3.64 SE) 

Midway populations (3 to 4 supplementations over 17years) 

Year 50 Probability of survival 0.86 

Year 100 Probability of survival 0.62 (0.05 SE) 

Mean time to first extinction 61.0 years (3.45 SE) 

Lisianski populations (3 to 4 supplementations over 17 years) 

Year 50 Probability of survival 0.97 

Year 100 Probability of survival 0.81 (0.03 SE) 

Mean time to first extinction 61.56 years (3.26 SE) 

Kaho’olawe population (yearly supplementation from captive flock for 17 years) 

 Year 50 Probability of survival 1.0 

 Year 100 Probability of survival 0.98 (0.01 SE) 

Mean time to first extinction 58. 71 years (12.9 SE) 

Main Island predator exclosure population (assumes supplementation alternate years 

from captive flock for 17 years) 

Year 50 Probability of survival 1.0 

 Year 100 Probability of survival 0.98 (0.01 SE) 

Mean time to first extinction 54. 0 years (17.78 SE) 
Laysan Duck Draft Revised Recovery Plan, August 2004. Appendix 3. 

94

Summary of Results for Mixed Islands Metapopulation – Combination of 

populations on Northwestern Hawaiian Islands and Main Hawaiian Islands: 

Mixed Islands Metapopulation 

Year 50 Probability of survival 1.0 

Year 100 Probability of survival 0.99 (0.01 SE) 

Mean time to first extinction 92.0 years (0.001 SE) 

Within Mixed population means 

Year 50 Probability of survival 0.92; number of extant populations 4.62 (0.78 SE) 

Year 100 Probability of survival 0.75 (0.02 SE) 

Mean time to first extinction 58.27 years (28.80 SE) 

Years with harvest and supplementation mean growth rate (r) = 0.1370 (0.2843 SE) 

Years without harvest or supplementation r = -0.0016 (0.2873 SE) 

Across all years mean r = 0.0081 (0.2907 SE)