Parasite and predator risk assessment: nuanced use of olfactory cues

Abstract

Foraging herbivores face twin threats of predation and parasite infection, but the risk of predation has received much more attention. We evaluated, experimentally, the role of olfactory cues in predator and parasite risk assessment on the foraging behaviour of a population of marked, free-ranging, red-necked wallabies (Macropus rufogriseus). The wallabies adjusted their behaviour according to these olfactory cues. They foraged less, were more vigilant and spent less time at feeders placed in the vicinity of faeces from dogs that had consumed wallaby or kangaroo meat compared with that of dogs feeding on sheep, rabbit or possum meat. Wallabies also showed a species-specific faecal aversion by consuming less food from feeders contaminated with wallaby faeces compared with sympatric kangaroo faeces, whose gastrointestinal parasite fauna differs from that of the wallabies. Combining both parasite and predation cues in a single field experiment revealed that these risks had an additive effect, rather than the wallabies compromising their response to one risk at the expense of the other.

Keywords: anti-predator behaviour; faecal aversion; foraging behaviour; macropodid marsupials; parasite avoidance; predator detection.

Figure 1.

The effects of the presence of the faeces of dogs, fed on different diets, on (a) the number of vigilance bouts and (b) the amount eaten (g) by red-necked wallabies. Values are means with standard error bars, with letters above indicating significant differences between treatments and numbers indicating sample size. (Online version in colour.)

Figure 2.

The combined effects of predator risk (the presence of dog faeces derived from different diets) and parasite risk (presence of conspecific and heterospecific macropod faeces) on: (a) the approach time (s); (b) the number of vigilance bouts; and (c) the amount eaten (g) by red-necked wallabies. Values are means with standard error bars. Connecting lines above the bars indicate non-significant (p > 0.05) differences between predator risk treatments, and an asterisk indicates significant differences between parasite risk treatments within predator risk treatments. (Online version in colour.)