Temporal patterns in echolocation and cave use by Guam Swiftlets (Aerodramus bartschi) in native and introduced habitat

Abstract

The Mariana Swiftlet (Aerodramus bartschi) is a federally listed endangered species of is native to Guam and the Marianas Islands. There is also a small, introduced population of Marianas Swiftlets on the island of Oahu, Hawaii. The nesting cave in Oahu is a small tunnel built for agricultural irrigation. Marianas swiftlets live in caves, which they navigate using echolocation clicks. Ecological Acoustical Recorders (EARs) were modified with a omni-directional microphone with a flat frequency response and −63 dB sensitivity for bird recordings. Data were recorded at a sample rate of 80,000 and a duty cycle of 30 s of recording every 5 min. BEARs (Bird EARs) were placed in swiftlet caves on Oahu, Hawaii, and Guam where they recorded for between five and fifteen days. Swiftlet clicks were detected using Ishmael’s energy sum detector. Temporal patterns of clicking were analyzed and compared between the two sites and correlated with environmental data over the recording period to determine effects of sub-optimal nesting habitat and changed weather patterns on the Oahu population compared to the native population in Guam.