Pacific Sheath-Tailed Bat American Samoa Emballonura Semicaudata Semicaudata Species Report April 2020
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Pacific Sheath-tailed Bat American Samoa Emballonura semicaudata semicaudata Species Report April 2020 U.S. Fish and Wildlife Service Pacific Islands Fish and Wildlife Office Honolulu, HI Cover Photo Credits Shawn Thomas, Bat Conservation International. Suggested Citation USFWS. 2020. Species Status Assessment for the Pacific Sheath Tailed Bat (Emballonura semicaudata semicaudata). April 2020 (Version 1.1). U.S. Fish and Wildlife Service, Pacific Islands Fish and Wildlife Office, Honolulu, HI. 57 pp. Primary Authors Version 1.1 of this document was prepared by Mari Reeves, Fred Amidon, and James Kwon of the Pacific Islands Fish and Wildlife Office, Honolulu, Hawaii. Preparation and review was conducted by Gregory Koob, Megan Laut, and Stephen E. Miller of the Pacific Islands Fish and Wildlife Office. Acknowledgements We thank the following individuals for their contribution to this work: Marcos Gorresen, Adam Miles, Jorge Palmeirim, Dave Waldien, Dick Watling, and Gary Wiles. ii Executive Summary This Species Report uses the best available scientific and commercial information to assess the status of the semicaudata subspecies of the Pacific sheath-tailed bat, Emballonura semicaudata semicaudata. This subspecies is found in southern Polynesia, eastern Melanesia, and Micronesia. Three additional subspecies of E. semicaudata (E.s. rotensis, E.s. palauensis, and E.s. sulcata) are not discussed here unless they are used to support assumptions about E.s. semicaudata, or to fill in data gaps in this analysis. The Pacific sheath-tailed bat is an Old-World bat in the family Emballonuridae, and is found in parts of Polynesia, eastern Melanesia, and Micronesia. It is the only insectivorous bat recorded from much of this area. These brown bats are small (weight approximately 0.2 ounces (oz); 5.7 grams (g)), communally roost in caves, overhangs, lava tubes or crevasses, and forage in forests on small insects (0.08–0.2 inches (in); 2–5 millimeters (mm)). The viability of the Pacific sheath-tailed bat was defined as the likelihood of persistence over time. Viability was assessed using three conservation biology principles: resiliency, representation, and redundancy. Specifically, survival and reproduction at the individual, population, and subspecies levels were described along with beneficial and detrimental factors that result in changes in resiliency, representation, and redundancy from historic time to the present. The best current information shows that the Pacific sheath-tailed bat persists as small and isolated populations on smaller islands in Fiji, and has been extirpated from historically occupied areas in Samoa, American Samoa, Rotuma, Vanuatu, and Tonga. The most significant threats to the continued existence of the subspecies include predation by nonnative mammals, human disturbance of roost caves, habitat loss due to deforestation and overgrazing by ungulates, and stochastic events such as tropical cyclones. The Pacific sheath-tailed bat is highly susceptible to extinction due to low redundancy (few remaining populations), low representation (due to highly reduced range), and low resilience (due to low fecundity - one pup per year; and high aggregation in single roosts). The bat is also vulnerable to sea level rise, extreme rain events, and increased storm severity due to its geographic location within Western Pacific tropical cyclone storm tracks, and a tendency to roost in caves adjacent to the sea. Under current conditions, losses of individuals and populations are expected to continue. In summary, predation, habitat modification, disturbance of roost caves, and the risk from extreme storms threaten the viability of the Pacific sheath-tailed bat in Fiji, Samoa, American Samoa, Rotuma, Vanuatu, and Tonga. Low numbers of individuals and populations in a contracted range, along with a low reproductive rate magnify the threats to viability. Existing regulatory mechanisms and conservation efforts do not adequately address these threats, which are likely to continue into the future. iii Table of Contents Cover Photo Credits ........................................................................................................................ ii Suggested Citation .......................................................................................................................... ii Primary Authors .............................................................................................................................. ii Acknowledgements ......................................................................................................................... ii Executive Summary ....................................................................................................................... iii List of Figures ................................................................................................................................. v List of Tables .................................................................................................................................. v Introduction ..................................................................................................................................... 1 Regulatory History ..................................................................................................................... 1 Methodology .............................................................................................................................. 2 Part 1. Life History and Historical Status ....................................................................................... 5 Species Description and Taxonomy ........................................................................................... 5 Life History ................................................................................................................................ 6 Historic Range, Distribution, and Population Status ................................................................. 7 Part 2. Current Conditions and Species Status.............................................................................. 12 Individual and Population Needs and Stressors ....................................................................... 12 Range-wide Species Needs and Stressors ................................................................................ 24 Conservation Actions ............................................................................................................... 25 Resiliency, Representation, and Redundancy of the Species ....................................................... 26 Resiliency ................................................................................................................................. 26 Representation .......................................................................................................................... 27 Redundancy .............................................................................................................................. 27 Literature Cited ............................................................................................................................. 28 iv List of Figures Figure 1. The three conservation biology principles of resiliency, redundancy, and representation, or the “3Rs.” Figure 2. Historic and current roost locations of the Pacific sheath-tailed bat. Figure 3. Historic bat roost locations in Samoa and American Samoa. Figure 4. Current and historic roost locations of the Pacific sheath-tailed bat in Fiji. Figure 5. Historic roost locations in Tonga. Figure 6. Forest cover in Fiji (data from Hansen et al. 2013). Figure 7. Forest cover in American Samoa (data from: Meyer et al. 2017). Figure 8. Forest cover in Western Samoa (data from Meyer 2017). Figure 9. Forest cover in Tonga (data from LINZ 2015). Figure 10. Cyclone tracks for the central South Pacific from 1898 to 2019. All data from Knapp et al. (2010) and NOAA IBTrACS (2019). List of Tables Table 1. Forest cover in Fiji (data from Hansen et al. 2013). Only islands with known bat roosts are specifically summarized. Table 2. Forest Cover Summary for the Samoan Archipelago (data from LINZ 2015 and Meyer et al. 2017). Table 3. Summary of Forest Cover on Islands with Historic Bat Roosts in Tonga (data from LINZ 2015). v Introduction This Species Report uses the best available scientific and commercial information to assess the status of the semicaudata subspecies of the Pacific sheath-tailed bat, Emballonura semicaudata semicaudata. This subspecies is found in southern Polynesia, eastern Melanesia, and Micronesia. Three additional subspecies of E. semicaudata (E.s. rotensis, E.s. palauensis, and E.s. sulcata) are not discussed here unless they are used to support assumptions about E.s. semicaudata, or to fill in data gaps in this analysis. The Pacific sheath-tailed bat is an Old-World bat in the family Emballonuridae, and is found in parts of Polynesia, eastern Melanesia, and Micronesia. It is the only insectivorous bat recorded from much of this area. These brown bats are small (weight approximately 0.2 ounces (oz); 5.7 grams (g)), communally roost in caves, overhangs, lava tubes or crevasses, and forage in forests on small insects (0.08–0.2 inches (in); 2–5 millimeters (mm)). Regulatory History The Pacific sheath-tailed bat semicaudata subspecies was listed by the United States Fish and Wildlife Service as Endangered in 2016 (USFWS 2016a). All subspecies were listed as Endangered (i.e., a very high risk