Discussion of “In-depth analysis of the emotional reactivity of American mink (Neovison vison) under behavioral tests”

We read the recent paper published in the Canadian Journal of Animal Science by Zieliński et al. (2019b) with interest, since more diverse research on mink temperament is very welcome. However, we are concerned that this paper may create confusion in the literature for the reasons outlined below. First and foremost, the terminology used is misleading. What the authors call the “empathic test” seems to be the same as the well-established “stick test” (both terms even being used in another of their papers, Zieliński et al. 2019a). The word “empathic” in English refers to the ability to recognize and understand or even share in the emotions of another individual; its use here, therefore, suggests the test measures this social capacity, which we have no reason to believe is involved. This is because: (i) the test used here has been validated as a temperament test (Malmkvist and Hansen 2002; Malmkvist et al. 2003) but not for measuring any social dimension [the only test used to measure social behaviour in mustelids has been the mirror test (Haage et al. 2013; Noer et al. 2015, 2016) under the assumption that it elicits conspecific recognition (Gallup 1968)]; (ii) research on the empathic capabilities of animals has to date been carried out only in social species (e.g., Ben-Ami Bartal et al. 2011; Sato et al. 2015), whereas mink are a solitary species (Dunstone 1993); and (iii) the authors themselves are not using it to test any hypotheses related to empathy or social contexts. Renaming an established temperament test with a term that implies social motivations in a solitary species without any biological basis to do so is not appropriate. Another terminology issue in Zieliński et al. (2019b) pertains to the label used for one of the categories the test distinguishes. The authors chose to call mink responses that do not clearly fit in any of the main temperament categories (aggressive, curious, or fearful) “neutral”. Although this fourth category has not been consistently named across previous work [“unknown” in Hansen (1996); “uncertain” in Malmkvist and Hansen (2002); “other” or “unresponsive” in Meagher et al. (2011)], the term “neutral” suggests something about the mink’s affective response. This is justified to some extent by the results, since these mink did not display overt signs of fear or aggression. However, since the probability of remaining “neutral” seems to have decreased when the test was repeated, it is likely that a number of these mink were fearful or otherwise inhibited from actively interacting with the stick in the first test. Therefore, we would suggest avoiding terminology that makes assumptions about the mink’s affective response, particularly when the behaviour observed might be due to methodological constraints (e.g., restricted time or space to respond to the novel situation) rather than having a biological basis. In addition, the authors incorrectly conflate the “glove test” described by Meagher et al. (2011) with the older test described by Trapezov (2000), known as “Trapezov’s hand test” (see e.g., Malmkvist and Hansen 2002, which the authors do cite). In the latter, the experimenter reaches into the cage and attempts to handle the mink, as described by the authors here. What we called the “glove test” similarly uses the gloved hand as the stimulus but otherwise follows the protocol of the stick test; the cage is not opened. This is a key difference, as the “glove test” is, therefore, less invasive than the “Trapezov’s hand test” (while the authors correctly point out the true Trapezov’s test is much more invasive than the stick test). This makes the glove and stick tests more welfare-friendly options for temperament testing where possible, with the glove test still being more sensitive to low levels of fear. Finally, the authors’ main conclusion seems to be that contact duration or “intensity” should be measured in addition to using the qualitative categories typically applied in the stick and glove tests, and yet, they do not justify why this should be done. Duration of