Guam, Post-storm Mariana swiftlet colony size and nest counts, 2023

The Yǻyaguak (Mariana Swiftlet; Aerodramus bartschi) is an endangered cave-roosting species native to Guam and southern Mariana Islands, Micronesia. On May 24-25, 2023, Guam was hit by the category-4 Typhoon Mawar, which brought wide-spread destruction to the island. Approximately 6 weeks prior to the typhoon in April 2023 we conducted surveys of the three known colonies of Yǻyaguak at Mahlac, Maemong, and Fachi caves. This April 2023 pre-Mawar survey provided a baseline population estimate prior to Typhoon Mawar’s landfall. In July 2023, we re-surveyed the caves to estimate colony size and assess whether the cave colonies experienced significant declines in the immediate aftermath of the storm. In November 2023, we conducted our regularly scheduled biannual surveys which provided a longer-term assessment of potential impacts from the typhoon. The data here presents the counts from July and November 2023, with the earlier counts obtained from earlier work.