Current view: Text account
Site description (2007 baseline):
Site location and context
The caves are sinkholes in limestone substrate, with multiple entrances (USFWS, 1992). Surrounding areas are forested and access to the caves is difficult. The caves, on land owned by the US Navy, has been established as part of a “No Disturbance” area and are managed under a Integrated Natural Resources Management Plan and in cooperation with the Guam National Wildife Refuge. Guam Swiftlets nest on the ceilings of the caves.
The Guam Comprehensive Wildlife Conservation Strategy (GDAWR, 2005) reported over 500 Guam Swiftlets in three small colonies in three caves in the center of Guam (Mahlac, Fachi, and Maemong (Firebreak 3) Caves). The majority of birds are located in the Mahlac Cave on the Naval Ordnance Annex in Southern Guam, although some individuals may use the caves interchangeably, and all three are located in the same areas. The caves are part of the Navy portion of the Guam National Refuge Overlay Refuge and as such are managed through cooperative agreements between the USFWS and the US Navy (USFWS, 2007), and in accordance with the Navy’s Integrated Natural Resources Management Plan mandated under the Sikes Act. The caves are located in forested area that is not readily accessible, on land owned by the US Navy. The US Navy has established Mahlac cave as a “No Disturbance” area (USFWS, 2004b) and initiated snake trapping in 2001. A survey conducted in 2000 estimated a population of 700-800 swiftlets at Mahlac Cave and far fewer birds at the other caves (DAWR, 2000). Recent sightings indicate that the population may be increasing (G. Grimm, pers. comm.). Although Mahlac Cave is the only cave to have confirmed use by swiftlets, there are reports that the swiftlets may be using all three caves interchangeably. Thus, all three caves (Mahlac, Fachi, and Maemong) are proposed as a single IBA.
The caves are sinkholes in limestone substrate, with multiple entrances (USFWS, 1992). Surrounding areas are forested and access to the caves is difficult.
Pressure/threats to key biodiversity
Control of the Brown Tree Snake remains the largest conservation concern. Snakes have been observed at entrances to the caves, although the natural predilection of the swiftlets to use the ceiling for nesting may offer some natural protection. Snake trapping was initiated at Mahlac Cave in 2001 (J. Quitugua, pers. comm.).
Conservation responses/actions for key biodiversity
Snake trapping was initiated at Mahlac Cave in 2001 (J. Quitugua, pers. comm.). Current management around caves includes the placement of snake traps using live mice as bait, although that method is labor-intensive (GDAWR, 2005).
The IBA has some sort of protection. It is located on lands owned by the US Government, which is liable to the US Endangered Species Act. The Guam Swiftlet is listed on the US ESA.
The IBA is located on lands owned by the US Government, which is liable to the US Endangered Species Act.
Recommended citation
BirdLife International (2024) Important Bird Area factsheet: Mahlac Caves (Guam (to USA)). Downloaded from
https://datazone.birdlife.org/site/factsheet/mahlac-caves-iba-guam-(to-usa) on 23/11/2024.
