Population Assessments of the Pacific Sheath-Tailed Bat and Mariana Swiftlet Active
Using thermal cameras, we are determining the population size and cave occupancy of the Mariana swiftlet and Pacific sheath-tailed bat. Both species face extirpation from the Northern Mariana Islands and are listed as endangered. Understanding the species' population status can assist in planning recovery efforts for both species.
Overview:
The Mariana swiftlet (chachaguak; Aerodramus bartschi) and Pacific sheath-tailed bat (payeyi; Emballonura semicaudata rotensis) are native and limited to habitat in the Northern Mariana Islands. Both species are insect eaters that depend on limestone caves for nests and roosting. Population threats to these species include habitat loss from agricultural forest clearing, invasion of foreign species, habitat destruction from feral goats, frequent disturbance of nests and roosts, pesticide use, predation by the brown treesnake (Boiga irregularis) and cyclonic storms. Once inhabiting many of the islands that comprise the Mariana archipelago, small groups of swiftlets persist on the islands of Aguiguan, Saipan, and Guam. The sheath-tailed bat remains only on Aguiguan.
Legally mandated recovery efforts for the Pacific sheath-tailed bat and its two subspecies are underway and include reintroducing some bats to other suitable habitats. A better understanding of roosting and foraging behavior, habitat, and timing can be used to inform relocation efforts for both subspecies. Our partner biologists with the Commonwealth of Northern Mariana Island government are currently planning these efforts.
On October 24, 2018, Super Typhoon Yutu - a category 5 tropical cyclone - passed slowly over Aguiguan with sustained winds of 180 miles per hour. The USFWS Strategic Habitat Conservation group assessed the loss of forest cover on Aguiguan from remote satellite imagery after the storm at 98–99 percent. Given the traits of the island’s bats and swiftlets, this significant event may have directly killed individuals and damaged their foraging habitat to a level that they could not survive after the storm. The effect of Super Typhoon Yutu on the island’s wildlife populations is a significant source of uncertainty.
Twilight and nocturnally active animals are difficult to detect and monitor. Surveys can have observer bias and difficulty distinguishing swiftlets from bats during low-light conditions. To overcome these problems, we conducted thermal video-based surveillance of cave entrances to derive population estimates.
Objectives:
-
Estimate total population sizes of the Pacific sheath-tailed bat and Mariana swiftlet on Aguiguan.
-
Produce cave-specific counts of bats and swiftlets, which can be used by managers to prioritize sites for conservation actions - these colonial species roost in aggregations.
-
Produce estimates of the population growth rate for the Pacific sheath-tailed bat.
-
Evaluate the timing of bat emergence and return to roosts, as well as the frequency, duration, and timing of any nighttime cave use.
-
Compare counts made with thermal video techniques to those conducted visually to evaluate potential bias of past surveys that may have resulted in undercounts.
-
Sample bat vocalizations at previously occupied caves, or caves that potentially could host bats. Equipment can sample vocalizations from outside the caves.
Using thermal cameras, we are determining the population size and cave occupancy of the Mariana swiftlet and Pacific sheath-tailed bat. Both species face extirpation from the Northern Mariana Islands and are listed as endangered. Understanding the species' population status can assist in planning recovery efforts for both species.
Overview:
The Mariana swiftlet (chachaguak; Aerodramus bartschi) and Pacific sheath-tailed bat (payeyi; Emballonura semicaudata rotensis) are native and limited to habitat in the Northern Mariana Islands. Both species are insect eaters that depend on limestone caves for nests and roosting. Population threats to these species include habitat loss from agricultural forest clearing, invasion of foreign species, habitat destruction from feral goats, frequent disturbance of nests and roosts, pesticide use, predation by the brown treesnake (Boiga irregularis) and cyclonic storms. Once inhabiting many of the islands that comprise the Mariana archipelago, small groups of swiftlets persist on the islands of Aguiguan, Saipan, and Guam. The sheath-tailed bat remains only on Aguiguan.
Legally mandated recovery efforts for the Pacific sheath-tailed bat and its two subspecies are underway and include reintroducing some bats to other suitable habitats. A better understanding of roosting and foraging behavior, habitat, and timing can be used to inform relocation efforts for both subspecies. Our partner biologists with the Commonwealth of Northern Mariana Island government are currently planning these efforts.
On October 24, 2018, Super Typhoon Yutu - a category 5 tropical cyclone - passed slowly over Aguiguan with sustained winds of 180 miles per hour. The USFWS Strategic Habitat Conservation group assessed the loss of forest cover on Aguiguan from remote satellite imagery after the storm at 98–99 percent. Given the traits of the island’s bats and swiftlets, this significant event may have directly killed individuals and damaged their foraging habitat to a level that they could not survive after the storm. The effect of Super Typhoon Yutu on the island’s wildlife populations is a significant source of uncertainty.
Twilight and nocturnally active animals are difficult to detect and monitor. Surveys can have observer bias and difficulty distinguishing swiftlets from bats during low-light conditions. To overcome these problems, we conducted thermal video-based surveillance of cave entrances to derive population estimates.
Objectives:
-
Estimate total population sizes of the Pacific sheath-tailed bat and Mariana swiftlet on Aguiguan.
-
Produce cave-specific counts of bats and swiftlets, which can be used by managers to prioritize sites for conservation actions - these colonial species roost in aggregations.
-
Produce estimates of the population growth rate for the Pacific sheath-tailed bat.
-
Evaluate the timing of bat emergence and return to roosts, as well as the frequency, duration, and timing of any nighttime cave use.
-
Compare counts made with thermal video techniques to those conducted visually to evaluate potential bias of past surveys that may have resulted in undercounts.
-
Sample bat vocalizations at previously occupied caves, or caves that potentially could host bats. Equipment can sample vocalizations from outside the caves.