Abstract
BackgroundWhy a variety of social animals emit foraging-associated calls during group foraging remains an open question. These vocalizations may be used to recruit conspecifics to food patches (i.e. food advertisement hypothesis) or defend food resources against competitors (food defence hypothesis), presumably depending on food availability. Insectivorous bats rely heavily on vocalizations for navigation, foraging, and social interactions. In this study, we used free-ranging big-footed myotis (Myotis macrodactylus Temminck, 1840) to test whether social calls produced in a foraging context serve to advertise food patches or to ward off food competitors. Using a combination of acoustic recordings, playback experiments with adult females and dietary monitoring (light trapping and DNA metabarcoding techniques), we investigated the relationship between insect availability and social vocalizations in foraging bats.ResultsThe big-footed myotis uttered low-frequency social calls composed of 7 syllable types during foraging interactions. Although the dietary composition of bats varied across different sampling periods, Diptera, Lepidoptera, and Trichoptera were the most common prey consumed. The number of social vocalizations was primarily predicted by insect abundance, insect species composition, and echolocation vocalizations from conspecifics. The number of conspecific echolocation pulses tended to decrease following the emission of most social calls. Feeding bats consistently decreased foraging attempts and food consumption during playbacks of social calls with distinctive structures compared to control trials. The duration of flight decreased 1.29–1.96 fold in the presence of social calls versus controls.ConclusionsThese results support the food defence hypothesis, suggesting that foraging bats employ social calls to engage in intraspecific food competition. This study provides correlative evidence for the role of insect abundance and diversity in influencing the emission of social calls in insectivorous bats. Our findings add to the current knowledge of the function of social calls in echolocating bats.
Highlights
Why a variety of social animals emit foraging-associated calls during group foraging remains an open question
Characteristics of social vocalizations A total of 3209 syllables belonging to 7 types were obtained in the focal foraging site of M. macrodactylus, namely bent downward frequency modulation, wrinkled downward frequency modulation, sinusoidal frequency modulation (SFM), flattened downward frequency modulation, steep downward frequency modulation, chevron frequency modulation-downward frequency modulation (CFMDFM), and downward paraboloid frequency modulationdownward frequency modulation (Fig. 1)
The duration of syllables ranged from 9.79 to 54.18 ms, and peak frequency ranged from 25.13 to 50.50 kHz. bent downward frequency modulation (bDFM) was the most commonly observed syllable, followed by wrinkled downward frequency modulation (wDFM) and steep downward frequency modulation (sDFM). bDFM had a relatively long duration (17.14 ± 2.74 ms), low frequency (37.25 ± 3.51 kHz) and large bandwidth (35.19 ± 7.34 kHz). bDFM was emitted in sequence at a high repetition rate. wDFM was an irregular wrinkling frequency modulated syllable
Summary
Why a variety of social animals emit foraging-associated calls during group foraging remains an open question These vocalizations may be used to recruit conspecifics to food patches (i.e. food advertisement hypothesis) or defend food resources against competitors (food defence hypothesis), presumably depending on food availability. Food-associated calls are social vocalizations produced by gregarious animals during foraging [16]. These vocalizations are usually loud, low frequency bouts facilitating long-range transmission of information [17]. The squeak calls from colonially nesting cliff swallows (Hirundo pyrrhonota) attract conspecifics to feed on ephemeral insect swarms [21] In these circumstances, the number of food-associated calls is predicted to be positively related to food availability and conspecifics’ foraging activities. In white-faced capuchins (Cebus capucinus) and red-bellied tamarins (Saguinus labiatus), individuals who called when they discovered food were less likely to be approached by other competitors [24, 25]
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