Is the propensity to emit alarm calls associated with health status?

The production and structure of animal signals may depend on an individual’s health status and may provide more than one type of information to receivers. While alarm calls are not typically viewed as health condition dependent, recent studies have suggested that their structure, and possibly their propensity to be emitted, depends on an individual’s health condition and state. We asked whether the propensity of yellow-bellied marmots (Marmota flaviventer) to emit calls is influenced by their immunological or parasite status, by quantifying both trap-elicited and natural calling rates as a function of their neutrophil-to-lymphocyte (NL) ratio, the presence of a blood borne trypanosome, and the presence of several intestinal parasites (Eimeria sp., Entamoeba sp., and Ascaris sp.). We fitted mixed effects models to determine if the health measures we collected were associated with the probability of calling in a trap and with annual rates of natural alarm calling. Marmots infected with a blood-borne trypanosome were marginally more likely to call naturally and when trapped, while those infected with the intestinal parasite Ascaris were less likely to call when trapped. NL ratio was not directly associated with in-trap calling probability, but males were more likely to call when they had higher NL ratios. Thus, health conditions, such as parasite infection and immune system activation, can modulate the production of alarm signals and potentially provide information to both predators and prey about the caller’s condition. Playback experiments are required to confirm if receivers use such information.