ALARM CALLING IN YELLOW-BELLIED MARMOTS .1. THE MEANING OF SITUATIONALLY VARIABLE ALARM CALLS

Yellow-bellied marmots, Marmota flaviventris, were reported to produce qualitatively different alarm calls in response to different predator s. To test this claim rigorously, yellow-bellied marmot alarm communic ation was studied at two study sites in Colorado and at-one site in Ut ah. Natural alarm calls were observed and alarm calls were artificiall y elicited with trained dogs, a model badger, a radiocontrolled glider and by walking towards marmots. Marmots 'whistled', 'chucked' and 'tr illed' in response to alarming stimuli. There was no evidence that eit her of the three call types, or the acoustic structure of whistles, th e most common alarm call, uniquely covaried with predator type. Marmot s primarily varied the rate, and potentially a few frequency character istics, as a function of the risk the caller experienced. Playback exp eriments were conducted to determine the effects of call type (chucks versus whistles), whistle rate and whistle volume on marmot responsive ness. Playback results suggested that variation in whistle number-rate could communicate variation in risk. No evidence was found of intrasp ecific variation in the mechanism used to communicate risk: marmots at all study sites produced the same vocalizations and appeared to vary call rate as a function of risk. There was significant individual vari ation in call structure, but acoustic parameters that were individuall y variable were not used to communicate variation in risk. (C) 1997 Th e Association for the Study of Animal Behaviour.