8 Observations of Scent-Marking and Discriminating Selffrom Others by a Domestic Dog (Canis familiaris): Tales of Displaced Yellow Snow
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8 Observations of Scent-Marking and Discriminating Self from Others by a Domestic Dog (Canis familiaris) Tales of Displaced Yellow Snow 1. INTRODUCTION Despite much interest in scent-marking by carnivores (Bekoff 1979a,b; Bekoff and Wells 1986; Gese and Ruff 1997; Allen et al. 1999 and references therein), there have been few experimental field studies of the phenomenon, and none such as the one described here in which clumps of urine-saturated snow (‘yellow snow’) were moved from one place to another to compare the responses of an individual to his own and other conspecific urine. Thus, little is known about urinating and marking behavior despite popular accounts that suggest otherwise, and there are few detailed field data concerning how free-ranging animals respond to their own and other conspecific urine. The purpose of the present study was to investigate the role of urine in eliciting urinating and scent-marking in a male domestic dog, Canis familiaris, by using a new approach for free-ranging individuals (others have used ‘yellow snow’ experiments to investigate reproductive conditions and individual discrimination of urine in captive canids (Brown and Johnston 1983; Mech et al., 1987; McCleod et al., 1996)). Tinbergen (1951/1989) stressed the importance of conducting simple field experiments. Moving yellow snow from place-toplace falls into this category. This type of experiment can also be used for other animals, and would yield important data concerning individual discrimination of their own and others’ scents and its influence on urinating, scent-marking, and territorial behavior. 2. METHODS Data were collected from October to April 1995 and from October to April 1997–2000 between 06:00 and 09:00 when there was snow on the ground. Jethro, a 35 kg neutered male mix (predominantly German Shepherd and Rottweiler castrated at 9 months of age) who has never mated, was observed as he sniffed his own and other dogs’ urine while he walked freely along a bicycle path paralleling Boulder Creek, just west of Boulder, Colorado (USA). Jethro was 5.5–10.5 years of age during the course of this experiment. Immediately after Jethro or other dogs (known males and females) urinated on Reprinted from Behavioural Processes 55. Bekoff, M. Observations of Scent-Marking and Discriminating Self from Others by a Domestic Dog (Canis familiaris): Tales of Displaced Yellow Snow, 75–79, 2001, with permission from Elsevier. snow, I scooped up the clump of yellow snow (about 4 cm × 4 cm) in gloved hands while Jethro was elsewhere and did not see me pick it up or move it. Before picking up urine the gloves were cleaned thoroughly using clean snow to minimize odor cues. I kept track of which other dogs were present and did not use the urine of the same dogs for at least 1 week, and Jethro had not previously sniffed the other dogs’ urine during a given session. After being moved, yellow snow was matted by hand into other snow to minimize visual cues. It was impossible to know whether all dogs were intact (not castrated), but when I was able to gather this information by observing males or by asking the human(s) accompanying the dogs I learned that all but three males and five females were neutered. The urine of two females in heat was not used. Yellow snow was moved so that Jethro arrived at the displaced urine: (i) within about 10 s (about 5–10 m down trail) of my placing it down; (ii) 10–120 s later (usually 10–50 m down trail); or (iii) 120–300 s later (more than 50 m down the trail). These intervals were chosen arbitrarily and might have to be changed for different experimental conditions. I also recorded the duration of sniffing (less than or greater than 3 s) using a stopwatch, whether Jethro urinated over the displaced yellow snow using the typical male raised-leg urination (RLU) posture, and whether or not he sniffed and then immediately urinated over the displaced yellow snow using the RLU posture. Sniffing immediately followed by directing urine towards a target is generally referred to as ‘scent-marking’ (Wells and Bekoff, 1981). Data were analyzed using proportions tests (Bruning and Kintz, 1977, p. 222ff) that generate the z statistic. I used P 1.96) to indicate significant differences between two percentages. The phrase ‘no significant difference’ or similar terms means that Z 0.05. Critical values of Z for other levels of statistical significance are 2.58 (P 3.30, P...