Mahlac Caves (24527)
Guam (to USA), Oceania
Site overview
KBA status: confirmed
Global KBA criteria: A1a, A1c
Year of last assessment: 2007
National site name: Mahlac Caves
Central coordinates: Latitude: 13.2333, Longitude: 144.7500
System: terrestrial
Elevation (m): 200 to 200
Area of KBA (km2): 1.46876
KBA classification: Global
Legacy site: Yes
Site details
Site description: 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.
Rationale for qualifying as KBA: This site qualifies as a Key Biodiversity Area of international significance that meets the thresholds for at least one criterion described in the Global Standard for the Identification of KBAs.
Additional biodiversity: 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.
Other site values: The IBA is located on lands owned by the US Government, which is liable to the US Endangered Species Act.
Delineation rationale: 2012-12-17 (BL Secretariat): original polygon clipped to hi-res coastline following identification in October 2012 of new marine IBA offshore this site; site area consequently updated (non-GIS) to 147 ha (GIS).
Habitats
Summary of habitats in KBA: The caves are sinkholes in limestone substrate, with multiple entrances (USFWS, 1992). Surrounding areas are forested and access to the caves is difficult.
Threats
Summary of threats to biodiversity at KBA: 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.).
| Threat level 1 | Threat level 2 | Threat level 3 | Timing |
|---|---|---|---|
| Invasive & other problematic species, genes & diseases | Invasive non-native/alien species/diseases | Named species | Ongoing |
Additional information
References: Guam Division of Aquatic and Wildlife Resources GDAWR (2005). Guam comprehensive Wildlife Conservation Strategy (GCWCS). Department of Agriculture, Mangilao, Guam,. USFWS (2007). Guam National Wildlife Refuge. Agency Website.