Archived 2010-2011 topics: Kauai Elepaio (Chasiempis sclateri) and Oahu Elepaio (Chasiempis ibidis): newly-split and Endangered?

Link to BirdLife species factsheet for Elepaio (pre taxonomic split)

Elepaio Chasiempis sandwichensis has been split into Hawaii Elepaio C. sandwichensis, Kauai Elepaio C. sclateri and Oahu Elepaio C. ibidis, following the American Ornithologists Union. Prior to this taxonomic change, C. sandwichensis was listed as Vulnerable under criterion B1a+b(i,ii,iii,iv,v) on the basis that the species had an Extent of Occurrence (EOO) estimated at 6,500 km2, in which its habitat is severely fragmented, its population was estimated to be declining at a rate of 25% over 10 years, and declines were observed, inferred or suspected in the EOO, Area of Occupancy, area, extent and/or quality of habitat and number of locations or sub-populations. Overall, these declines are driven by habitat loss for urban development and agriculture, unfavourable habitat management, the effects of introduced species, including pathogens, and catastrophic weather events.

This taxonomic change has prompted a review of the threat status of the relevant taxa, and it is proposed that C. sclateri and C. ibidis both be listed as Endangered. C. sclateri qualifies as Endangered under the B1 criteria because it has an EOO estimated at 420 km2 on Kaua`i, in which its habitat is considered to be severely fragmented and the species is provisionally suspected to be in decline based on past evidence and ongoing threats. A decline is suspected based on a reduction of c.50% in the species’s population following Hurricane Iniki in 1992 (Pratt 1994); however, this may have been temporary (Jacobi and Atkinson 1995).

C. ibidis qualifies as Endangered under the B1 criterion and potentially the C criterion. The species is eligible for Endangered status under the B1 criteria because it has an EOO estimated at 240 km2, in which its habitat is considered to be severely fragmented, and ongoing declines are provisionally suspected based on past evidence and ongoing threats. It potentially qualifies as Endangered under the C criterion on the basis that it has a population of c.1,800 mature individuals (USFWS 2006), which is provisionally suspected to be declining. However, to qualify the species must be shown to be declining at a rate of at least 20% over 12 years (estimate of two generations), or have sub-populations that number 250 individuals or less, or have one sub-population that contains at least 95% of all mature individuals. If the decline recorded by VanderWerf et al. (2001) of over 75% since 1975 is ongoing, the species may well meet the stipulated trend threshold. This could also qualify the species for threatened status under the A criterion, which stipulate that the population trend must be at least a 30% decline over 18 years (estimate of three generations) in the past, future or both. The ongoing threats of habitat loss for urban development and agriculture, fires and introduced species, including pathogens, seem to be particularly prevalent on O`ahu.

Comments are invited on these proposed listings under the IUCN criteria and detailed information is requested on the severity of threats and level of habitat fragmentation on both O`ahu and Kaua`i, and the estimated population trend and sub-population structure of both species.

Jacobi, J. D. and Atkinson, C. T. (1995) Hawaii’s endemic birds. Pp. 376-381 in LaRoe, E.T., ed. Our living resources: a report to the nation on the distribution, abundance, and health of US plants, animals, and ecosystems. Washington, D.C.: U.S. Department of the Interior, National Biological Service.

Pratt, H. D. (1994) Avifaunal change in the Hawaiian Islands, 1893-1993. Stud. Avian Biol. 15: 103-118.

U. S. Fish and Wildlife Service (2006) Revised Recovery Plan for Hawaiian Forest Birds. Honolulu, Hawaii: U.S. Fish and Wildlife Service.

VanderWerf, E. A., Rohrer, J. L., Smith, D. G. and Burt, M. D. (2001) Current distribution and abundance of the O’ahu ‘Elepaio. ‘Elepaio 61: 55, 57-61.

Related posts:

  1. Archived 2010-2011 topics: Hawaii Elepaio (Chasiempis sandwichensis): retain as Vulnerable?
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3 Responses to Archived 2010-2011 topics: Kauai Elepaio (Chasiempis sclateri) and Oahu Elepaio (Chasiempis ibidis): newly-split and Endangered?

  1. Oahu
    • Based on surveys conducted in the 1990s, VanderWerf et al. (2001) found that:
    o The species had declined by over 75% since 1975.
    o The population size was about 1,974 individuals, but that the breeding population was smaller, only 1,768 individuals, as a result of a biased sex ratio caused by nest predation on females by alien black rats.
    o The total size of the current range was small, only 5,486 hectares.
    o The distribution was highly fragmented, with six larger populations and many small fragments.
    • More recent surveys conducted from 2006-2010 by VanderWerf et al. (in press) in the Waianae Mountains of western Oahu found that the decline has continued.
    o The total population of Oahu Elepaio in the Waianae Mountains was found to be only 300, including 108 breeding pairs and 84 single males. This area was estimated to support about 950 elepaio in the 1990s, which was about half the total population at that time.
    o The range is highly fragmented, and all subpopulations have declined.
    o Oahu Elepaio have disappeared entirely from some portions of the Waianae Mountains, meaning there are now fewer subpopulations and the range is even more fragmented and smaller.
    • Surveys currently are being conducted in the Koolau Mountains of eastern Oahu. Preliminary data indicate the range and number of elepaio have declined somewhat in this region, but not as severely as in the Waianae Mountains (VanderWerf unpubl. data).
    • The total size of the area currently occupied by the species has not been estimated since the 1990s, but it has declined substantially from the previous estimate of 5,486 hectares, perhaps by as much as 30%.
    • Major threats to the Oahu Elepaio are ongoing and occur throughout the species range, including nest predation by alien black rats, diseases carried by alien mosquitoes, and habitat degradation caused by invasive alien plants (VanderWerf 2009). Rats are being controlled in several areas and this has reduced the threat, but only a small proportion of the total population currently benefit from this management and rat control is needed on a larger scale (VanderWerf 2009).
    • Based on the information above this species may qualify for categorization as Critically Endangered.

    USGS has more details on the status of this species, but in general its numbers appear to have increased recently, despite a range contraction since 1968-1973, primarily at lower elevations. Its status is not nearly as dire and that of the Oahu Elepaio, and they should not be categorized similarly. Endangered status is not warranted, vulnerable would be more appropriate.

  2. References:
    VanderWerf, E.A., S.M. Mosher, M.D. Burt and P. E. Taylor . In Press. Current distribution and abundance of O’ahu ‘Elepaio (Chasiempis ibidis) in the Wai’anae mountains. Pacific Science 65(3).

    VanderWerf, E.A. 2009. Importance of nest predation by alien rodents and avian poxvirus in conservation of Oahu elepaio. Journal of Wildlife Management 73:737-746.

    VanderWerf, EA, Young, LC, Yeung, NW, Carlon, DB. 2009. Stepping stone speciation in Hawaii’s flycatchers: Molecular divergence supports new island endemics within the elepaio. Conservation Genetics 11:1283-1298. DOI 10.1007/s10592-009-9958-1

    VanderWerf, E. A. 2008. Sources of variation in survival, recruitment, and natal dispersal of the Hawai’i ‘Elepaio. Condor 110:241-250.

    VanderWerf, E. A. 2007. Biogeography of `Elepaio: evidence from inter-island song playbacks. Wilson Journal of Ornithology 119:325-333.

  3. In light of the taxonomic split of Elepaio (Chasiempis sandwichensis), much of the assessment described in the current BirdLife factsheet, and the resulting Endangered designation, appears to be no longer applicable to the Kaua`i `Elepaio (C. sclateri). Some of the following information may be found in Camp & Gorresen, in press. Design of forest bird monitoring for strategic habitat conservation on Kaua`i Island, Hawai`i. Hawai`i Cooperative Studies Unit technical report); the rest is unpublished.

    • population probably single contiguous deme (ie, not fragmented);
    • occurs within the full extent of the 69-80 km2 area (Alaka`i Plateau and Koke`e region) surveyed from 2005-2008; the 2008 population estimate mean for this area = 28,506 (95%CI = 14,256-36,666); occupancy across area surveyed in 2000 = 96% (SE=2%)
    • 1968-1973 range ≈ 379 km2; current extent not known, but lowest recent record was at 900m (Walther 1995); habitat area >900m = 185 km2, which indicates that the range may be only about ½ as large as in 1968-1973 period
    • population significantly increasing; annual rate of change = 0.0378 (95%CI = 0.0330—0.0427) for the 25 km2 interior portion of the Alaka`i Plateau sampled from 1981 to 2008; in the larger area (across plateau) the population is also significantly increasing (13% increase in mean density between 2000 and 2008)
    • inter-annual density variability low to moderate; coefficient of variation (CV) = 0.29 for the full extent of the 69-80 km2 area (Alaka`i Plateau and Koke`e region) sampled between 2000 and 2008; CV = 0.43 for the 25 km2 interior portion of the Alaka`i Plateau sampled from 1981 to 2008

    In summary, despite the apparent historical contraction in range (since the 1968-1973 period) and the current small range, the species’ trend since the 1981 is positive, inter-annual densities are not highly variable, and the range is not likely fragmented. Given the above, we feel that the Kaua`i `Elepaio does not meet criteria for the Endangered status. However, given the uncertainty in various other criteria, the Vulnerable status may be warranted.

    Walther, M. 1995. Forest bird distribution and abundance west of the Alaka`i Wilderness Preserve, Kaua`i, Summer 1994. `Elepaio 55:35-36.

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