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1

Geographic variation in the echolocation calls of the hoary bat ( Lasiurus cinereus)

100%
Farrell M. J. O., Corben C., Gannon W. L.
Acta Chiropterologica
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2000
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tom 02
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nr 2
Use of bat detectors to perform inventories, determine activity, and assess differential use of habitats has become a generally accepted method. However, there has been vigorous disagreement as to the level of efficacy, primarily relating to the ability to distinguish certain species and groups of species. The primary explanation suggested for the inability to identify certain species is due to the magnitude of intraspecific variation resulting in overlap among species, presumably compounded by geographic variation. Lasiurus cinereus has been identified as exhibiting the greatest degree of geographic variation including recent findings of distinct variation between populations in Hawaii and Manitoba. We find that claims of geographic variation have not been proven because of small sample size and lack of adequate description of method, including the behavior of the bat and the context during which bats were recorded. Previous geographical comparisons of species have relied on standard statistical methods that do not allow a comprehensive examination of the range in variation of diagnostic call parameters. We present data from a broad range of sites throughout mainland United States and Hawaii, and compare a multivariate statistical approach with repertoire plots of characteristic frequency versus call duration. Although we demonstrated a statistical finding of geographic variation in L. cinereus, small sample size, context, and behavior could not be discounted as the proximal cause of observed variation. The perceived variation across the geographic range that we sampled did not affect our ability to identify the species by call structure. We suggest methods for future studies of geographic variation.
2

The efficacy of acoustic techniques to infer differential ose of habitat by bats

100%
Sherwin R. E., Gannon W. L., Haymond S.
Acta Chiropterologica
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2000
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tom 02
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nr 2
The use of acoustic detectors to investigate differential use of habitat by bats has become increasingly common. However, in many of these studies, authors failed to clearly articulate assumptions a priori. For example, spatial and temporal scales were rarely defined. True replication is rarely reported, suggesting that authors assume that these systems are both spatially and temporally static. In this study, we attempted to clearly identify underlying assumptions of this technique, thereby limiting level of inference to a clearly defined and repeatable degree. We followed strict assumptions beforehand and were able to classify bat calls into guilds based on acoustic data. Lack of experience in acoustic identification by technicians did not affect the outcome, as guilds were based on bat call sequences following strict rules of classification. Individuals in guilds were not randomly distributed across sample locations. However, distribution of guild members did not suggest differential use of habitat, as within habitat variation was often greater than that observed among types of habitat. Explicitly stating assumptions before surveys were conducted ‘protected’ us from making incorrect inferences. We suggest that care be taken when attempting to infer differential use of habitat by bats using acoustic techniques.
3

Pinnae and echolocation call differences between Myotis californicus and M. ciliolabrum ( Chiroptera: vespertilionidae)

100%
Gannon W. L., Sherwin R. E., DeCarvalho T. N., O`Farrell M. J.
Acta Chiropterologica
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2001
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tom 03
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nr 1
We measured the shape of pinnae from fluid-preserved, museum specimens of 33 Myotis californicus and 39 M. ciliolabrum and cranial characters from 40 skulls of each species. We also measured 40 specimens of Eptesicus fuscus, which were used as an outgroup. Significant differences were found in aural shape and tragus height between the two species of Myotis. Archived echolocation calls from the two species from across the range segregated, further suggesting that morphological and call characters are intercorrelated. We tested this relationship using 17 M. californicus and 12 M. ciliolabrum captured in the field for external measurements and echolocation call recordings (n = 1,124 calls in 52 call files, x = 2.3 call files per released bat), and found significant differences (most P < 0.001) in pinnae and call morphology between M. ciliolabrum and M. californicus similar to those observed in ‘museum’ samples. We found that small interspecific differences in pinna shape and size are correlated with differences in the frequency ranges (larger pinna, lower frequency).
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