Function of social calls in Brown Long-eared bats Plecotus auritus

Murphy, Stephanie E (2012) Function of social calls in Brown Long-eared bats Plecotus auritus. Doctoral thesis (DPhil), University of Sussex.

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Abstract

Microchiropteran bats produce vocalisations for two purposes: echolocation and communication. Vocalisations used for communication are often referred to as social calls. In this thesis I examined the nature of Brown Long-eared bats Plecotus auritus social calls recorded at roost and foraging sites through a combination of recording and playback
experiments.

A total of 11,484 social calls were recorded at 20 maternity roosts sites and three types of vocalisations were dentified on the basis of shape, referred to as Type A, B, and C. Although Type A vocalisations shared the same basic pattern, it was a very large group within which there was a lot of variation in acoustic parameters. Principal component analysis and modelbased cluster analysis were used to look for patterns within this group, and this identified six clusters. Maternity colonies surveyed in this study varied in size from as few as nine up to 98 bats, and the number of social calls recorded at the roost sites was highly correlated with the numbers of bats present in the colony. The analysis of seasonal patterns of social call production revealed that the number of social calls recorded at maternity roost sites showed a linear increase from June to September, whereas, the number of bats emerging decreased sharply from August to September.

Simulations of P. auritus social calls were used to investigate behavioural responses to calls away from roost sites using the Autobat. P. auritus were clearly much more responsive to simulations of their own species' social calls than to the other stimuli tested. This strongly suggests that the responses to the Autobat represent attempts to interact with the source of the stimulus. Recording with ultrasound and infra-red video was conducted to test the bats’ responses to the different types of synthesised call and whether these responses varied seasonally.

A female’s approach response to the stimulus may represent an attempt to repel a perceived intruder from her foraging area. Alternatively, if calls were used to coordinate foraging by advertising the location of resources to other females that share the range, a response may represent an attempt to move towards such resources. Experiments showed that females were significantly more likely to respond to a stimulus produced within their core foraging area, than in the peripheral area, or outside their foraging area. On the other hand, while females regularly shared foraging ranges with other females, there was little evidence of co-ordination of movements between simultaneously radio-tracked dyads. It was concluded that responses to the stimuli probably represent attempts to repel perceived intruders from the foraging area.

The thesis concludes with a discussion of some of the advantages and limitations of using play-back of synthesised social calls in the field to investigate vocal communication in bats. Ways in which studies of captive bats of known relatedness could be used to further elucidate the functions of social calls are discussed.

Item Type: Thesis (Doctoral)
Schools and Departments: School of Life Sciences > Biology and Environmental Science
Subjects: Q Science > QL Zoology > QL0605 Chordates. Vertebrates > QL0700 Mammals > QL0737 Systematic divisions. By order and family, A-Z > QL0737.C5 Chiroptera (General works)
Depositing User: Library Cataloguing
Date Deposited: 06 Jul 2012 09:49
Last Modified: 04 Sep 2015 14:10
URI: http://sro.sussex.ac.uk/id/eprint/39750

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