The Hawaiian hoary bat (Lasiurus cinereus semotus) is the only bat on the Hawaiian archipelago (Tomich, 1986); moreover, as the only extant, endemic, terrestrial mammal to Hawai’i, the Hawaiian hoary bat (HHB) is Hawai’i’s officially designated state land mammal (Senate Bill 1183, 2015). The bat is listed as globally imperilled by NatureServe (Accessed: 05Nov1996), and as endangered under both the U.S. Endangered Species Act (USESA, LE: Listed endangered 13Oct1970) and Hawai‘i endangered species laws (Hawai‘i Administrative Rules 13-124, Exhibit 2 and Hawai‘i Revised Statutes (HRS) §195D). Despite being federally listed as endangered, there remains little empirical information concerning the ecology and life history of this bat - its current population, yearly trends and elements identified as primary data needs for species recovery (USFWS 1998, Gorresen et al., 2013) remain unknown on the island Moloka’i and in Kalaupapa National Historical Park (KNHP).
Bats are considered a vital component of many ecosystems, they are both ecologically and economically important mammals, yet their global population status continues to be a concern due to White Nose Syndrome, and other influences. Bat populations are vulnerable to declines due to low reproductive rates, specialized habitat needs, exposure to human disturbances, diseases, and natural disasters. Consequently, monitoring and conservation of bat populations has become an elevated priority for resource managers.
Current information regarding natural history and population status of the HHB is scarce, resulting in incomplete and, occasionally, conflicting reports. This is further compounded by the fact that the HHBs are highly mobile, wide-ranging mammals; thus rendering it difficult to ascribe habitat associations and population values. Nevertheless, we identify the HHB as a vital component of many ecosystems; they are insectivorous bats with high metabolic rates, and therefore of particular economic importance as predators of a diversity of pest insects (Wund and Meyers, 2005). Furthermore, bats are the only mammals possessing true wings and powered flight, allowing them to transverse to parts of the world that are rarely populated by flightless or gliding mammals; this makes them particularly important to mammalian biodiversity in geographically isolated areas such as the Hawaiian Islands. Indeed, the endemic HHB is the only indigenous terrestrial mammal extant bat established in the islands (Stone and Pratt, 2002).
A lack of accurate information makes it difficult to effectively and proactively manage HHB. Prior attempts to understand the HHB on Topside Moloka’i and in KNHP were hampered by complex topography, clumsy equipment, and a complicated analytical process of the raw data; showing very limited success, with only a few detections over a 1-year period (Fraser and HaySmith, 2009). Our study, has been acoustically monitoring the HHBs, successfully detecting bats with an increasing detection to effort ratio - exceeding detections by past monitoring.
This study aims to define HHB spatial and temporal data on Mokoka’i; providing empirical information that could address long-term trends whilst also informing about their current status - safeguarding our bats against potential threats.
This study is based of a sample of extant HHB ultrasonic echolocation recordings made between February 2016 until June 2018, representing 12987 hours of recording effort. 31857 HHB pulses were recorded across 146 locations on the island of Molokai by both NPS and Aka’ula School.
Map of Moloka'i Showing Each of the 146 Recording Locations.
The sample represents data across a range of elevation (m.), locations and weather effects. All data was collected using Anabat Express (Titley Electronics) bat detectors, recorded on SD memory cards and transferred to a Windows PC for analysis using SPSS and ARCGIS. Location and elevation data was recorded using Garmin 64s GPS units.
A wide range of methods may be employed in order to accurately census bats, with popular techniques including visual roost count, emergence count, hibernation counts, mark-recapture studies, and echolocation analysis. However, the appropriate use of such methods very greatly depending on species size, mobility, spatial and trophic niche use, number of individuals present, access to roosting sites, and available equipment; moreover, the validity of some such techniques have indeed been questioned (Kunz, 2003).
The Hawaiian hoary bats, like all genus Lasiurus, are solitary foliage-roosting bats (Carter et al., 2003), visual counts of such cryptic bats are complicated due to their widely dispersed, difficult to locate nature (Kunz, 2003).
Whilst visual roost counts can provide an estimate of a colony’s size at popular roosting sites, obtaining absolute abundance is generally unrealistic; this method best applies to localized areas where all roost sites are known and accounted for (British Columbia Resources Inventory Committee, 1998). Additional methods such as evening emergence counts, evening dispersal counts, and disturbance counts are also unsuitable for monitoring Hawaiian hoary bats due to their solitary and cryptic roosting behaviour. Emergence counts are better suited for colonial bats, while dispersal and disturbance counts are typically more appropriate for censusing megachiropterans (Kunz 2003).
All bats belonging to the suborder Microchiroptera use ultrasonic acoustics, echolocation, in order to avoid obstacles and locate prey. This bat echolocation is beyond the frequency of human hearing; but ultrasonic monitors can detect bat calls, producing visible images that reveal the presence, or absence, of bats. Moreover, acoustic bat detectors reveal further details regarding features of their calls – delineating feeding activity (Thomas and West 1989) from search/contact calls, therefore making it possible to document foraging areas used by the bat.
Optimal long-term monitoring favours acoustic ultrasonic echolocation recording equipment due to the passive, cost-efficient and non-invasive benefits of the detections (O’Shea and Bogan, 2003). Acoustic methods can be implemented passively, collecting data that facilitates statistically rigorous analysis, but crucially accommodates observation, identification, and study without intervention.
Since February 2016 Anabat Express bat monitors were placed in the field for one to two week intervals, rotating through the same sites throughout the seasons of the year. Bats are nocturnal, therefore the monitors were programmed to record ultrasonic sounds from dusk until dawn when bats are more likely to be active. Once the recording interval has ended the detectors are collected, and the data is filtered in AnalookW to remove noise, then analysed statistically in SPSS and visually in GIS against a backdrop of GIS based data layers. Site locations were initially selected in order to replicate an earlier study, later expanded to new locations through the park, then ultimately to the island of Moloka’i. The attempt has been to survey a wide variety of environments to gain a measure of bat activity across Moloka’i in both space and time. In September 2016 Aka’ula School were allocated Anabat Express bat monitors, and pupils were encouraged to sample any areas that appealed to them – this dramatically increased the sample area from the confines of KNHP to the boundaries of Molokai itself. Aka’ula School are responsible for 23.23% (243 nights) of sampled locations, detecting 9270 HHB pulses, 26.45% of total detected pulses.
AnalookW Unfiltered Ultrasonic Detections For One Night Recording
AnalookW Filtered Ultrasonic Recordings Demonstrating Calls Characteristic of Bats
Prior research proposed the hypothesis that HHB are more active during their breeding season, April until August. We tested this, and discovered the following:
HHB breeding season was entered as a predictor into a simple linear regression (enter method) with echolocation detections as the outcome variable. This produced a statistically significant model F(1, 1044) = 3.95, p<0.05, but with an R² = 0.01. Normalizing echolocation detections by hours of recording effort produced a similar result, F(1, 1044) = 5.157, p<0.05 with an R²=0.01. Using season as a predictor variable did make a significant contribution to the model, β = 0.061, p<0.05; but this would suggest that only 6% of the variation in bat detections can be attributed to the breeding season. 94% of the variation can not be explained by season alone.
Kalaupapa is separated from the rest of Moloka'i by a 1700 ft. sea cliff - the tallest in the world. Testing whether or not elevation can predict HHB pulses produced the following results:
Detector elevation (m) was entered as a predictor in to a linear regression (enter method) with detected Hoary Bat pulses as the outcome variable. This did not produce a statically significant model, F(1, 1044) = .973, p>0.05 with an R² of 0.01. 0.1% of the variance of recorded Hoary Bat pulses is attributed to elevation differences. The predictor variable did not significantly contribute to the model β = -0.031 p >0.05, This result suggests that abundance of Hawaiian Hoary Bat pluses is not associated with differences in elevation.
How do Weather Conditions Influence Results?
Weather factors; solar radiation, wind speed, temperature, humidity and precipitation (in.) were entered as predicators in to a multiple regression (enter method), with Hawaiian Hoary Bat pulse count as the outcome variable. This did not produce a statically significant model, F(11, 1030) = 1.198, p >0.05 with an R² of 0.01. These results would suggest that differing weather variables do not influence HHB detection rates.
Where are Bats Detected?
This map charts each detector location, visualising counts of HHB echolocation pulses. The darker and larger the circle the greater the sum of pulses at that site.
This map charts each detector location, visualising counts of HHB echolocation pulses per hour of recording effort. The darker and larger the circle the greater the number of pulses at that site per hour of recording effort.
Collaborative partnership with schoolchildren of Aka`ula School has bolstered research efforts at KNHP, rendering a broader empirical understanding of HHB activity - not simply within the park, but across Moloka’i. Incorporating pupils’ local knowledge with discrete data has been key in constructing a more encompassing understanding of HHB trends on the island.
Aka'ula School are responsible for testing 23.23% of surveyed locations, recording for 243 nights.
Aka'ula School detection efforts account for 26.45% of HHB bat detections, detecting 9270 echolocation pulses.
In total Aka'ula School accounts for 27.50% of HHB detections per hour of recording effort.
Without these efforts our data would simply be limited to the confines of the Kalaupapa peninsula itself. But by enthusing the curiosity of the pupils, encouraging them to survey their homes or places of personal interest we have not only added data to our analysis, but have helped facilitate excitement for investigation of their local environment. These bats are not only elusive and difficult to see if present, but they produce sounds beyond the human capacity to perceive. It is important to develop an understanding of the human relationship with the natural world; but as humans we can have a tendency to be unaware of things we can not see, and thus unaware of the human impact on those unseen elements. This collaborative work has helped reveal the presence of this critical mammal to some of the youth of the island. Hopefully helping them to connect to their local environment for things that are not always directly seen, but are still present and important.
Pupils have not only learned about this "invisible" animal around them, but also the importance the HHB has for Hawai'i and the ecosystem they inhabit. Additionally, the pupils have learned about science in general, by fully participating in the investigation and analysis process. Evening excursions with youth to actively detect bats using a Wildlife acoustics "Echo Meter Touch" provided an exciting real-time adventure searching for bat roosting areas - this was very popular indeed.
It will be important to foster this knowledge that critical elements of nature may be around you, even if we can not see them, or their effects. Equally it will be important to promote participation in conservation discussion with regards to the local environment. Engaging the minds of the youth today, may potentially bode well for the future of the HHB and human relationships of the future.
These results correlate with prior attempts to understand these small animals. Namely that they are elusive, difficult find, and difficult to fully understand. Many observations regarding HHB are conflicting, and our results do not currently outright define patterns that can easily be understood. Factors we thought may influence HHB activity, such as elevation, climate, or season have not proven to significantly influence detection success. However, what we have determined is bat presence, absence and abundance in certain areas of the island of Moloka'i.
This has been important as it has contributed to an understanding of HHB range and abundance within areas of KNHP. Fish and Wildlife Service directives are to curtail vegetation management during the bat roosting period. This can be an inconvenience since the time of pupping falls within the time when the park is preparing for the upcoming hurricane season. Preparation for hurricane season includes the removal of vegetation, often large trees proximal to roads and powerlines bisecting areas of potential bat habitat. Kalaupapa NHP has also embarked on an extensive program of fuel reduction within the settlement as well as at select locations across the Kalaupapa Peninsula. Proving that we have no bat activity these areas of management has helped ensure that human decisions within KNHP are not adversely affecting our HHB population and habitat.
The overlap of spatial/temporal bat and human activity/management prompt the need for a better understanding of bat distribution relative to park management activities. In order to fully understand this relationship we will require further metrics of measurement, anecdotally it appears the HHB have a preference for inhabiting non-native vegetation, but only by gathering addition measurements of habitat can we hope to tease apart a relationship.
This study will not only continue, but expand. Only by doing so can we aim to understand this perplexing species. Only by understanding it's behaviour can we implement sound strategies aimed to protect Hawaii’s only native terrestrial mammal.
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