Vocalization toward conspecifics in silver foxes (Vulpes vulpes) selected for tame or aggressive behavior toward humans

Abstract

We examined the production of different vocalizations in three strains of silver fox (unselected, aggressive, and tame) attending three kinds of behavior (aggressive, affiliative, and neutral) in response to their same-strain conspecifics. This is a follow-up to previous experiments which demonstrated that in the presence of humans, tame foxes produced cackles and pants but never coughed or snorted, whilst aggressive foxes produced coughs and snorts but never cackled or panted. Thus, cackle/pant and cough/snort were indicative of the tame and aggressive fox strains respectively toward humans. Wild-type unselected foxes produced cough and snort toward humans similarly to aggressive foxes. Here, we found that vocal responses to conspecifics were similar in tame, aggressive and unselected fox strains. Both cackle/pant and cough/snort occurred in foxes of all strains. The difference in the use of cackle/pant and cough/snort among these strains toward humans and toward conspecifics suggest that silver foxes do not perceive humans as their conspecifics. We speculate that these vocalizations are produced in response to a triggering internal state, affiliative or aggressive, that is suppressed by default in these fox strains toward humans as a result of their strict selection for tame or aggressive behavior, whilst still remaining flexible toward conspecifics.

Figure 1

Spectrogram illustrating call types produced toward conspecifics by silver foxes: (a) whine of a Tame fox, (b) moo of a Tame fox, (c) growl of a Tame fox, (d) bark of an Aggressive fox, (e) cackle of an Aggressive fox, (f) pant of an Aggressive fox, (g) snort of a Tame fox, (h) cough of a Tame fox.

Figure 2

Mean values (and SE as whiskers) for calling rates of particular call types during neutral (Ne), affiliative (Af) and agonistic (Ag) behaviors in Unselected, Aggressive and Tame study groups, and the differences between the behaviors and groups revealed with MANOVA followed by Newman-Keuls post hoc tests: *** P < 0.001 ** P < 0.01; * P < 0.05.

Figure 3

Mean values (and SE as whiskers) for overall calling rates during neutral (Ne), affiliative (Af) and agonistic (Ag) behaviors in Unselected, Aggressive and Tame study groups, and the differences between the behaviors and groups revealed with MANOVA followed by Newman-Keuls post hoc tests: *** P < 0.001 ** P < 0.01; * P < 0.05.

Figure 4

Numbers and proportions of tested fox pairs that produced particular call types in each study group: U – Unselected, A – Aggressive, T – Tame. Horizontal lines show mean values for numbers of tested fox pairs producing the given call type, the results of all comparisons between the observed and mean values with Fisher exact test are non significant.

Figure 5

Numbers and proportions of Unselected, Aggressive and Tame fox pairs that produced along to other call types both cough/snort and cackle/pant, only cough/snort, only cackle/pant, or neither cackle/pant nor cough/snort.