Signal Interactions Between Native and Introduced Forest Birds of Hawaiʻi Island and Predicting Distance of Signals from Their Energy

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2023-12
Authors
Hunt, Noah James
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Hart, Patrick J.
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Tropical Conservation Biology & Environmental Science
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Passive acoustic monitoring using autonomous recording units (ARUs) offers uniqueopportunities to investigate both theoretical and applied ecological questions. I used Song Meter SM4s to answer: (1) whether native and introduced birds in Hawaiʻi are dividing acoustic space in time and frequency, and (2) whether wildlife managers can improve their density estimates of bird species by achieving unbiased distance measurements from ARUs. First, using recordings I collected from a diversity of vegetation types, I compared the observed overlap between introduced and native bird vocalizations from what was expected under a null model of 500 vocalization randomizations. I found that overlap did not differ from the null distribution and was unaffected by community composition nor vegetation type, suggesting that introduced birds are not having a strong impact on native forest bird communication. Second, using field recordings collected while observing vocalizing birds, I modeled distances between birds and the ARUs, measured from range finders as a function of the random effects of maximum power level (amplitude) of bird vocalizations, the orientation of the bird to the microphone, and wind and rain levels, with the species and call type as fixed effects. Overall, there was no strong relationship between distance and any of the random effects. However, when modeling within individual call types, I found four call types among four species showing relationships between distance and sound power level, suggesting that while this method has potential for wildlife monitoring, it requires further refinement.
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Biology, acoustic niche hypothesis, acoustic overlap, density estimation, distance-power relationship, population monitoring, signal partitioning
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54 pages
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