Hawaii Wildlife Ecology Lab

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    Successful nesting by 2 endangered Hawaiian waterbird species in a restored Indigenous wetland agroecosystem
    ( 2022-03-01) Kristen C. Harmon, Eryn N. P. Opie, Ali‘i Miner, Iokepa Paty-Miner, Jonathan K. Kukea-Shultz, Kawika B. Winter, and Melissa R. Price
    The Hawaiian Stilt (Himantopus mexicanus knudseni) and Hawaiian Gallinule (Gallinula galeata sandvicensis) are federally endangered waterbirds endemic to the Hawaiian Islands. Both species are conservation-reliant; their population persistence is dependent on invasive predator control and removal of invasive plants that degrade habitat. We present observations of successful nesting by one Hawaiian Stilt pair and one Hawaiian Gallinule pair at a site managed within an adaptive Indigenous agroecological framework on the island of O‘ahu, Hawai‘i. The Hawaiian Stilt nest, found in February 2019, contained 4 eggs and produced 3 hatchlings, 2 of which were banded and monitored after hatching. The Hawaiian Gallinule nest, found in February 2020, contained 6 eggs and produced 5 hatchlings. Although no individuals were banded from this nest, 2 adults and 2 hatchlings were continuously observed in the nesting area after the eggs hatched. Lo‘i kalo Hawaiian wetland agroecosystems centered around the cultivation of kalo (taro; Colocasia esculenta), have the potential to expand Hawaiian waterbird habitat beyond state and federal protected areas. We are aware of unpublished accounts of Hawaiian waterbirds nesting in commercially farmed lo‘i kalo, but until now, there have been no previously published accounts of native waterbirds breeding in lo‘i kalo managed as Indigenous agroecosystems.
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    First observations of Least Tern (Sternula antillarum) eggs and other breeding observations on the island of O‘ahu, Hawai‘i
    (AllenPress, 2021-08-04) Harmon, Kristen ; Phipps, Clarine ; VanderWerf, Eric ; Chagnon, Bethany ; Price, Melissa
    The Least Tern (Sternula antillarum) commonly breeds along coastal beaches and major interior rivers of North America and the Caribbean. Least Terns have been observed in Hawai‘i since the 1970s; however, few breeding attempts have been documented. Nests have been discovered on the northwestern Hawaiian island of Midway Atoll and the southeastern Hawaiian island of Hawai‘i. While nesting is thought to also occur on the islands of O‘ahu and French Frigate Shoals based on observations of juvenile Least Terns, no observations of nests had been recorded for these islands prior to this study. In this paper we describe 2 accounts of discovering Least Tern eggs in the Ki‘i Unit of the James Campbell National Wildlife Refuge on O‘ahu, as well as several observations of breeding behavior in wetlands within the Pearl Harbor region of O‘ahu.
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    The role of Indigenous practices in expanding waterbird habitat in the face of rising seas
    (Elsevier, 2021-04-01) Harmon, Kristen ; Winter, Kawika ; Kurashima, Natalie ; Fletcher, Charles ; Kane, Haunani ; Price, Melissa
    In Hawai‘i, as is the case globally, sea level rise threatens the availability of suitable habitat for waterbirds and other coastal species. This study examines Hawaiian wetland agro-ecosystems (loʻi) as social-ecological systems that may meet human needs while expanding nesting habitat of endangered waterbirds, if restored under an Indigenous Resource Management paradigm. We applied spatial analysis to project: (1) the area of existing waterbird habitat likely lost to sea level rise by the end of the century (2100); and (2) the area of waterbird habitat potentially gained through restoration of lo‘i systems. Results show that, if loʻi offer similar or equivalent habitat value to Hawaiian waterbirds as conventionally managed wetlands, the restoration of loʻi would not only compensate for projected losses of wetland habitat due to sea level rise, but substantially contribute toward the recovery of endangered waterbirds that are currently habitat-limited. This study demonstrates capacity for contemporary Indigenous land management to address conservation and food-security needs in the Hawaiian Islands, as well as challenges of multi-objective land use and habitat restoration for endangered wetland-dependent fauna. This research further contributes toward a growing number of studies suggesting that Indigenous practices based on social-ecological frameworks offer potential to achieve sustainability and biodiversity goals simultaneously.
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    Cooperative breeding behaviors in the Hawaiian Stilt (Himantopus mexicanus knudseni)
    (Wiley, 2021-03-10) Dibben-Young, Arleone ; Harmon, Kristen ; Lunow-Luke, Arianna ; Idle, Jessica ; Christensen, Dain ; Price, Melissa
    Cooperative breeding, which is commonly characterized by nonbreeding individuals that assist others with reproduction, is common in avian species. However, few accounts have been reported in Charadriiformes, particularly island-nesting species. We present incidental observations of cooperative breeding behaviors in the Hawaiian Stilt (Himantopus mexicanus knudseni), an endangered subspecies of the Black-necked Stilt (Himantopus mexicanus), during the 2012–2020 nesting seasons on the Hawaiian islands of O‘ahu and Moloka‘i. We describe two different behaviors that are indicative of cooperative breeding: (a) egg incubation by multiple adults; (b) helpers-at-the-nest, whereby juveniles delay dispersal and reproduction to assist parents and siblings with reproduction. These observations are the first published accounts of cooperative breeding in this subspecies and merit further investigation, as cooperative breeding may improve population viability of the endangered, endemic Hawaiian Stilt.
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    Seasonal patterns in nest survival of a subtropical wading bird, the Hawaiian Stilt (Himantopus mexicanus knudseni)
    (PeerJ, 2021-02-01) Harmon, Kristen ; Wehr, Nathaniel ; Price, Melissa
    Nest survival is influenced by where and when birds decide to breed. For ground-nesting species, nest-site characteristics, such as vegetation height and proximity to water, may impact the likelihood of nest flooding or depredation. Further, habitat characteristics, and thus nest survival, may fluctuate across the breeding season. The Hawaiian Stilt (‘Ae‘o; Himantopus mexicanus knudseni) is an endangered Hawaiian waterbird that nests in wetlands across the Hawaiian Islands. In this study, we used observational surveys and nest cameras to examine the impact of nest-site characteristics and day of nesting season on nest survival of the Hawaiian Stilt. Early nests had a higher chance of survival than late nests. For most of the nesting season, taller vegetation was correlated with increased nest survival, while shorter vegetation was correlated with increased nest survival late in the nesting season. Seasonal patterns in nest survival may be due to changes in parental behavior or predator activity. Nest depredation was responsible for 55% of confirmed nest failures and introduced mammals were the primary nest predators. Our study is the first to examine seasonality in nest survival of Hawaiian Stilts and suggests that, despite longer nesting seasons and year-round occupation of wetlands, late nesters in subtropical regions may have lower nest survival than early nesters, similar to trends observed in temperate regions.
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    Cooperative Breeding Behaviors in the Hawaiian Stilt (Himantopus mexicanus knudseni)
    ( 2021-03-17) Dibben-Young, Arleone ; Harmon, Kristen ; Lunow-Luke, Arianna ; Idle, Jessica ; Christensen, Dain ; Price, Melissa
    Cooperative breeding, which is commonly characterized by non-breeding individuals that assist others with reproduction, is common in avian species. However, few accounts have been reported in Charadriiformes, particularly island-nesting species. We present incidental observations of cooperative breeding behaviors in the Hawaiian Stilt (Himantopus mexicanus knudseni), an endangered subspecies of the Black-necked Stilt (Himantopus mexicanus), during the 20122020 nesting seasons on the Hawaiian islands of O‘ahu and Moloka‘i. We describe two different behaviors that are indicative of cooperative breeding: (1) egg incubation by multiple adults; (2) helpers-at-the-nest, whereby juveniles delay dispersal and reproduction to assist parents and siblings with reproduction. These observations are the first published accounts of cooperative breeding in this subspecies and merit further investigation, as cooperative breeding may improve population viability of the endangered, endemic Hawaiian Stilt.
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    Nest depredation risk increases later in the nesting season for a subtropical wading bird, the Hawaiian Stilt (Himantopus mexicanus knudseni)
    ( 2020-04-29) Harmon, Kristen ; Wehr, Nathaniel ; Price, Melissa
    Nest depredation is the leading cause of nest failure in avian species. While depredation risk largely depends on depredation pressure, it may also be influenced by the timing of the nesting season and by nest site features, such as proximity to water and vegetation height. The Hawaiian Stilt (Himantopus mexicanus knudseni) is an endangered Hawaiian waterbird that nests in wetlands across the Hawaiian Islands from February to September. The nesting season coincides with a seasonal decline in precipitation, which may impact depredation rates. In this study, we used observational surveys and nest cameras to examine the impact of nest-site characteristics and nest initiation date on nest depredation of the Hawaiian Stilt. We found that stilts preferred shorter vegetation than what was randomly available and preferred to nest in Pickleweed (Batis maritima) rather than other available plant species. However, nest-site characteristics, such as vegetation height and distance to water, did not have an impact on depredation risk. Early nests had a higher chance of survival than late nests. The number of depredated nests peaked later in the nesting season, and introduced mammals were the primary nest predators. Increasing invasive predator control later in the Hawaiian Stilt nesting season, particularly for mammalian predators, may increase nest survival of later nesters. Our study is the first to examine seasonality in nest depredation of Hawaiian Stilts and suggests that, despite longer nesting seasons and year-round occupation of wetlands, late nesters in subtropical regions may have greater depredation risk than early nesters, similar to trends observed in temperate regions.
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    Nesting Ecology of the Hawaiian Stilt (Himantopus mexicanus knudseni) on O‘ahu
    ( 2020-04-20) Price, Melissa ; Harmon, Kristen ; Idle, Jessica ; Christensen, Dain ; Opie, Eryn
    The Hawaiian Stilt (Himantopus mexicanus knudseni) is an endangered subspecies of the Black-necked stilt (Himantopus mexicanus) that inhabits wetlands throughout the Hawaiian Islands. Depredation of eggs and chicks by introduced predators is a major threat to Hawaiian Stilt populations. Where and when a bird decides to nest may impact the likelihood of egg or chick depredation. Nesting in close proximity to water may decrease depredation rates by mammals, as water can act as a barrier to mammalian predators, does not hold scent, and provides an obstacle-free escape route for chicks. Alternatively, some mammalian predators may be attracted to water, and a number of aquatic species have been identified as predators of Hawaiian Stilt chicks, including the American Bullfrog (Lithobates catesbeianus). Vegetation height is also an important factor for egg and chick survival, as taller vegetation may help conceal nests and chicks from predators, particularly aerial species. Additionally, depredation is often not constant across the breeding season due to changes in parental activity, nest and chick abundance, or habitat characteristics. The Hawaiian Stilt nests from February to September across the Hawaiian Islands. The nesting season coincides with a seasonal decline in precipitation, which may alter habitat characteristics and thus impact depredation rates. Further, management tools, such as mammal-exclusion fencing, are currently in use and may greatly increase egg and chick survival. The objectives of this project were to: 1) identify habitat characteristics important for nest-site selection and chick habitat use; 2) identify factors that impact hatching and fledging success. We found that stilts preferred to nest in shorter vegetation than what was available and preferred Pickleweed (Batis maritima) rather than other available plant species. However, nest-site characteristics, such as vegetation height and distance to water, did not have an impact on egg depredation risk. Early nests had a higher chance of hatching than late nests. The number of depredated nests peaked later in the nesting season, following a peak in nest initiation. Introduced mammals were the primary egg predators and included rats (Rattus spp.), feral cats (Felis catus), and Small Indian Mongooses (Herpestes auropunctatus). The number of eggs laid, as well as hatching success, was greater inside the mammal exclusion fence at Honouliuli Wetland, compared to a nearby site without a fence, Waiawa Wetland, where mammalian predators are only excluded via trapping. The average home range size for 12 tracked pre-fledglings was 0.94 ± 1.42 acres, and most chicks were observed using vegetated mudflats near open water. Of the 20 chicks that were tracked in this study, 7 fledged (35%), 6 had unknown fates (30%), 4 died due to unknown causes (20%), 2 were depredated by a feral cat (10%), and 1 died due to emaciation (5%). Our results suggest that management of predators, particularly mammals, is key to improving stilt hatching success, as preferred nest-site characteristics do not reduce the likelihood of egg depredation. Tall, invasive vegetation, such as California Grass (Brachiaria mutica), should continue to be controlled, as it was rarely used for nesting. More desirable vegetation, such as Pickleweed, should be made available throughout wetlands to encourage larger spacing between nesting pairs, which may help to reduce egg depredation pressure. Increasing mammalian predator control later in the nesting season may also increase hatching success of later nesters. Alternatively, mammal-exclusion fencing may provide year-round protection from mammalian predators, increasing both egg and chick survival. More data is needed to form conclusions regarding home range and survival of Hawaiian Stilt chicks. Improved detection methods and radio-tagging attachment styles will be used in the 2020 nesting season, which will reduce uncertainties and improve statistical power of analyses.
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    Dining local: the microbial diet of a snail that grazes microbial communities is geographically structured
    ( 2015) O’Rorke, Richard ; Cobian, Gerald ; Holland, Brenden ; Price, Melissa ; Costello, Vincent ; Amend, Anthony
    Achatinella mustelina is a critically endangered tree snail that subsists entirely by grazing microbes from leaf surfaces of native trees. Little is known about the fundamental aspects of these microbe assemblages: not taxonomic composition, how this varies with host plant or location, nor whether snails selectively consume microbes. To address these questions, we collected 102 snail faecal samples as a proxy for diet, and 102 matched-leaf samples from four locations. We used Illumina amplicon sequencing to determine bacterial and fungal community composition. Microbial community structure was significantly distinct between snail faeces and leaf samples, but the same microbes occurred in both. We conclude that snails are not ‘picky’ eaters at the microbial level, but graze the surface of whatever plant they are on. In a second experiment, the gut was dissected from nonendangered native tree snails in the same family as Achatinella to confirm that faecal samples reflect gut contents. Over 60% of fungal reads were shared between faeces, gut and leaf samples. Overall, location, sample type (faeces or leaf) and host plant identity all significantly explained the community composition and variation among samples. Understanding the microbial ecology of microbes grazed by tree snails enables effective management when conservation requires captive breeding or field relocation.
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    Demographic and genetic factors in the recovery or demise of ex situ populations following a severe bottleneck in fifteen species of Hawaiian tree snails
    ( 2015-11-12) Price, Melissa ; Sischo, David ; Pascua, Mark-Anthony ; Hadfield, Michael
    Wild populations of endangered Hawaiian tree snails have declined precipitously over the last century due to introduced predators and other human impacts. Life history traits, such as very low fecundity (<5 offspring per year across taxa) and maturity at approximately four years of age have made recovery difficult. Conservation efforts such as in situ predator-free enclosures may increase survival to maturity by protecting offspring from predation, but no long-term data existed prior to this study demonstrating the demographic and genetic parameters necessary to maintain populations within those enclosures. We evaluated over 20 years of evidence for the dynamics of survival and extinction in captive ex situ populations of Hawaiian tree snails established from wild-collected individuals. From 1991 to 2006, small numbers of snails (<15) from fifteen species were collected from the wild to initiate captive-reared populations as a hedge against extinction. This small number of founders resulted in a severe bottleneck in each of the captive-reared populations.We identified key demographic parameters that predicted population recovery from this bottleneck. Species with captive populations that produced between two and four offspring per adult per year and had 20–50% of those offspring survive to maturity recovered to numbers above 100 individuals, and maintained viable populations following a decline that occurred between 2009 and 2014. Those populations that had less than two offspring per adult per year and less than 20% survival to maturity did not reach 100 individuals in captivity, and many of these populations died out during the recent decline. We suggest that small reductions in fitness may contribute to extirpation in taxa with inherently low fecundity, by keeping populations below a threshold number essential to long-term recovery. Future ex situ populations should be founded with no less than 15 adults, and maintained in conditions closely approximating the temperature and humidity of source locations to optimize fitness. Permanent translocations of wild populations for conservation purposes will be more likely to succeed with greater than 100 adults, and should be limited to locations with a similar climate to source locations.