Mariana Swiftlet Population Analysis
Population counts of Mariana swiftlets is critical to understand if control of brown tree snakes in Guam have aided swiftlet recovery. USGS scientists and The University of Hawai’i at Hilo are testing videographic methods to count Mariana swiftlet population size and observe their nesting and roosting behavior.
Overview:
The Mariana Swiftlets - Aerodramus bartschi - is the only endangered bird species persisting in the wild in Guam, restricted to three caves on the U.S. Naval Magazines in southern Guam, and two other Mariana Islands: Aguiguan and Saipan.
Historically, the swiftlets were abundant on Guam, but following the introduction of brown tree snakes - Boiga irregularis; BTS - Guam populations declined steeply. Swiftlet population sizes increased over the last several decades but appear to be decreasing in recent years. However, population estimates are not very accurate, as the method of counting birds returning to their roosts in the evening is known to have multiple sources of error. It is unknown to what degree swiftlet numbers change seasonally and annually. We are developing thermal and infrared cameras to help visualize and count swiftlets to increase the accuracy and repeatability of population numbers.
The decline in population size in recent years, despite continued BTS control, and small populations in two of three caves, creates uncertainty in whether the current BTS control is effective or whether other factors contribute to inhibiting population growth. Of particular interest, why are swiftlets limited to just three caves? Historically, swiftlets occupied many caves around Guam.
Objectives:
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Estimate swiftlet population size over time. Using thermal cameras, film night roosts and cave entrance traffic two to three times a year to estimate population size for each cave, seasonal changes, and changes over time.
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Map roosting and nesting locations. Develop and test low power time-lapse thermal cameras to visualize roost locations and nests within caves to document seasonal changes and changes in roosting areas over time in response to BTS control.
-
Estimate nest success and nesting season. Develop analytical software to analyze time-lapse imagery to detect thermal signatures of active nests and monitor the time a nest is active to estimate nest success.
-
Estimate survival. Capture and band adult and subadult swiftlets at Mahlac and Maemong caves, establishing a marked population that will be the foundation for eventual mark/recapture survival estimates.
-
Determine movement patterns within caves and surrounding landscapes. Attach lightweight radio transmitters to a subset of swiftlets to track movement in and out of the caves and the surrounding areas around the caves.
Population counts of Mariana swiftlets is critical to understand if control of brown tree snakes in Guam have aided swiftlet recovery. USGS scientists and The University of Hawai’i at Hilo are testing videographic methods to count Mariana swiftlet population size and observe their nesting and roosting behavior.
Overview:
The Mariana Swiftlets - Aerodramus bartschi - is the only endangered bird species persisting in the wild in Guam, restricted to three caves on the U.S. Naval Magazines in southern Guam, and two other Mariana Islands: Aguiguan and Saipan.
Historically, the swiftlets were abundant on Guam, but following the introduction of brown tree snakes - Boiga irregularis; BTS - Guam populations declined steeply. Swiftlet population sizes increased over the last several decades but appear to be decreasing in recent years. However, population estimates are not very accurate, as the method of counting birds returning to their roosts in the evening is known to have multiple sources of error. It is unknown to what degree swiftlet numbers change seasonally and annually. We are developing thermal and infrared cameras to help visualize and count swiftlets to increase the accuracy and repeatability of population numbers.
The decline in population size in recent years, despite continued BTS control, and small populations in two of three caves, creates uncertainty in whether the current BTS control is effective or whether other factors contribute to inhibiting population growth. Of particular interest, why are swiftlets limited to just three caves? Historically, swiftlets occupied many caves around Guam.
Objectives:
-
Estimate swiftlet population size over time. Using thermal cameras, film night roosts and cave entrance traffic two to three times a year to estimate population size for each cave, seasonal changes, and changes over time.
-
Map roosting and nesting locations. Develop and test low power time-lapse thermal cameras to visualize roost locations and nests within caves to document seasonal changes and changes in roosting areas over time in response to BTS control.
-
Estimate nest success and nesting season. Develop analytical software to analyze time-lapse imagery to detect thermal signatures of active nests and monitor the time a nest is active to estimate nest success.
-
Estimate survival. Capture and band adult and subadult swiftlets at Mahlac and Maemong caves, establishing a marked population that will be the foundation for eventual mark/recapture survival estimates.
-
Determine movement patterns within caves and surrounding landscapes. Attach lightweight radio transmitters to a subset of swiftlets to track movement in and out of the caves and the surrounding areas around the caves.