What you see is not what you get: the role of ultrasonic detectors in increasing inventory completeness in Neotropical bat assemblages

1. Microchiropteran bats have the potential to be important biodiversity indicator species as they are distributed globally and are important in ecosystem functioning. Survey and monitoring protocols for bats are often ineffective as sampling techniques vary in their efficacy depending on the species involved and habitats surveyed. Acoustic sampling using bat detectors may prove an alternative or complementary technique to capture methods but is largely untested in the tropics. 2. To compare the efficacy of bat detectors and capture methods in surveys, we used ground mist nets, sub-canopy mist nets and harp traps to sample bats while simultaneously recording the echolocation calls of insectivorous bats in a diversity of habitats in the Yucatan, Mexico. We described echolocation calls, analysed call characteristics to identify species, and compared species inventories derived from traditional capture methods with those derived from acoustic sampling. 3. A total of 2819 bats representing 26 species and six families were captured; 83% were captured in ground nets, 13% in sub-canopy nets and 4% in harp traps. Fourteen species and five phonic types were identified based on five echolocation call characteristics. Discriminant function analysis showed a high level of correct classification of the calls (84·1%), indicating that identification of species by their echolocation calls is feasible. 4. In all habitats, acoustic sampling and capture methods sampled significantly more species each night than capture methods alone. Capture methods failed to sample 30% of the bat fauna, and aerial insectivores were sampled only by bat detectors. 5. Synthesis and applications. Given the importance of bats in ecosystem functioning, and their potential as indicator species, developing effective methodologies to survey and monitor bats is important for sustainable forest management and biodiversity conservation. Acoustic sampling should be used with capture methods to increase inventory completeness in bat assemblage studies, and could form part of a single standardized monitoring protocol that can be used globally in tropical forests, as this method detects aerial insectivores not sampled by capture methods.