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Monitoring long-tailed bat (Chalinolobus tuberculatus) activity and investigating the effect of aircraft noise on bat behaviour in a modified ecosystem

Echolocating bats are one of the most diverse and cryptic mammalian groups. Individuals are typically small, nocturnal, highly mobile, and rely on high frequency (greater than 20 kHz) vocalisations (i.e. echolocation pulses and social calls) inaudible to humans. It is estimated that a quarter of the more than 1,200 recognized bat species are threatened, which has largely been attributed to habitat loss through anthropogenic activities. Therefore, a need exists to improve our understanding of bat behaviour, habitat use and how anthropogenic activities might impact bats, especially in modified habitats. A primary aim of New Zealand’s Bat Recovery Plan (1995) is to develop ways to effectively monitor bats to define distributions and identify conservation needs for specific populations: this would better focus bat management and conservation strategies. My research objectives were to: monitor the spatial and temporal activity patterns of long-tailed bats (Chalinolobus tuberculatus; LTBs) at two exotic forest fragments on the edge (Hammond Bush) and outskirts (an oak fragment) of Hamilton City (North Island, New Zealand) and conduct a field-based playback experiment to assess whether aircraft noise alters bat activity. In Chapter 2, I monitored the spatial and temporal foraging activity of LTBs across different: nights; seasons; habitats; microhabitats (both vertical and horizontal dimensions); and varying environmental conditions, including an anthropogenic variable (frequency of aircraft overflights at the oak fragment). Foraging activity was variable over time, but nightly peaks occurred between the first and third hours after sunset. Pass rates were significantly higher at both habitats during spring and summer compared with winter. At the oak fragment, significantly more bat detections were recorded when detectors were placed at a height of 4-7m (compared with 15-30m); a similar non-significant trend was observed at Hammond Bush. A greater proportion of bat passes were recorded in microhabitats containing water bodies and open spaces. Mean nightly temperature was the only significant positive predictor of bat activity (at the oak fragment only). To maximise LTB detections in future monitoring studies so that resources can be better focused, I recommend that bats be monitored: 1.) during warmer months; 2.) on warmer nights; 3.) by placing detectors at heights of 4-7m; and 4.) by placing detectors in forested habitats near open spaces and water bodies. In Chapter 3, I concurrently monitored LTB activity at four rural and urban sites over three consecutive seasons and conducted a presence/absence survey at 11 sites along the rural-urban interface of Hamilton City. I sought to apply monitoring recommendations at different habitats and determine how LTBs are distributed in relation to distance from anthropogenic structures (e.g. roads and houses) and riparian margins. LTBs used multiple rural and urban sites across successive seasons; however, bat activity was lower at sites not situated adjacent to the Waikato River compared with sites on the riverbank. I detected LTBs at eight of 11 sites surveyed confirming that this species is more widely distributed in the Hamilton region than previously shown. I did not detect bats at urban sites surrounded by roads and houses. Both proximity to riverine habitat and anthropogenic structures (e.g. roads) may influence LTB distribution and habitat use. In Chapter 4, I showed that in addition to echolocation pulses, bat detectors also record some in-flight LTB calls. I classified LTB calls and tracked three common call types (chirps, pulses and buzzes) over the LTB breeding season (December-March). Pulses and buzzes were recorded around the time of female pregnancy to lactation, and lactation to juvenile volancy, respectively. These calls were only recorded at the oak fragment and were often associated with multi-bat echolocation sequences. Pulses and buzzes may be situation-specific social calls mediating interactions between reproductive females. Chirps were frequently recorded (89% of calls were chirps) across all months at both sites. Chirps may be more generally associated with foraging behaviour (e.g. aiding echo discrimination) as peaks in chirps overlapped with foraging activity. Tracking in-flight calls should alert researchers to sites of likely social importance to LTBs. Call function/s should be further investigated using playback experiments. In Chapter 5, I used a combination of correlative and experimental playback methods to investigate whether aircraft activity and noise alters the evening activity of free-living LTBs. Correlative data revealed that low-altitude aircraft activity overlapped with bat activity at the oak fragment. Bat activity decreased during and after aircraft passes but this trend was not statistically significant. It also appears that bats decrease their activity more during louder aircraft passes. Playback trials revealed that simulated aircraft noise did not significantly alter bat behaviour compared with baseline activity levels and a silent control. Results suggest that aircraft noise may not disturb LTB behaviour or mask high frequency echolocation pulses.
Type of thesis
Le Roux, D. S. (2010). Monitoring long-tailed bat (Chalinolobus tuberculatus) activity and investigating the effect of aircraft noise on bat behaviour in a modified ecosystem (Thesis, Master of Science (MSc)). University of Waikato, Hamilton, New Zealand. Retrieved from https://hdl.handle.net/10289/4999
University of Waikato
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