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The site was identified as internationally important for bird conservation in 2007 because it was regularly supporting significant populations of the species listed below, meeting IBA criteria.

Populations meeting IBA criteria ('key species') at the site:

Species	Red List	Season (year/s of estimate)	Size	IBA criteria
Mariana Swiftlet Aerodramus bartschi	VU	breeding (2000)	700 individuals	A1, A2

Ideally the conservation status of the IBA will have been checked regularly since the site was first identified in 2007. The most recent assessment (2014) is shown below.

State (condition of the key species' populations)
Species	Actual vs Reference (units)	% remaining	Result
Mariana Swiftlet Aerodramus bartschi	1,000 / 1,000 (individuals)	100	favourable

Pressure (threats to the key species and/or their habitats)
Threat	Timing	Scope	Severity	Result
Invasive and other problematic species and genes	happen­ing now	whole popul­ation/area (>90%)	slow deteri­oration (1–10% over 3 gener­ations)	high

Response (conservation actions taken for the key species and/or their habitats)
Designation	Planning	Action	Result
Whole area of site (>90%) covered by appropriate conservation designation	A compre­hensive and appropriate manage­ment plan exists that aims to maintain or improve the popul­ations of qualify­ing bird species	Substantive conservation measures are being implemented, but these are not comprehensive and are limited by resources and capacity	high

Year	Protected Area	Designation (management category)	% coverage of IBA
1993	Guam	National Wildlife Refuge (IV)	26

The IBA is located on lands owned by the US Government, which is liable to the US Endangered Species Act.

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Recommended citation
BirdLife International (2025) Important Bird Area factsheet: Mahlac Caves (Guam (to USA)). Downloaded from https://datazone.birdlife.org/site/factsheet/mahlac-caves-iba-guam-(to-usa) on 04/01/2025.