Observations of scent-marking and discriminating self from others by a domestic dog (Canis familiaris): tales of displaced yellow snow

Little is known about what stimuli trigger urinating or scent-marking in domestic dogs, Canis familiaris, or their wild relatives. While it is often suggested that the urine of other animals influences urinating and scent-marking patterns in canids, this has not been verified experimentally. To investigate the role of urine in eliciting urinating and marking, in this pilot study I moved urine-saturated snow ('yellow snow') from place-to-place during five winters to compare the responses of an adult male domestic dog, Jethro, to his own and others' urine. Jethro spent less time sniffing his own urine than that of other males or females, and that while his interest in his own urine waned with time it remained relatively constant for other individuals' urine. Jethro infrequently urinated over or sniffed and then immediately urinated over (scent-marked) his own urine. He marked over the urine of other males more frequently than he marked over females' urine. The method used here can be extended to other species for which experimental data are lacking. Though based on one dog, these novel data may further our knowledge of the role of scent-marking in territorial behavior and of sex differences in territory acquisition and maintenance.     

Scent-marking in the grey short-tailed opossum (Monodelphis domestica)

The characteristics and social determinants of scent-marking behaviour were studied in a laboratory colony of grey short-tailed opossums (Monodelphis domestica), a small Brazilian didelphid. Scent-marking was sexually dimorphic, occurring more frequently and displayed at higher levels in males. Sexually immature males did not scent-mark; males just past the age of puberty (5 months) marked at low levels; and older males marked at high levels using the head, flank and chest. Male M. domestica preferentially scent-marked objects and areas previously marked by other males. Females showed interest in the scent-marks of males. We discuss similarities in scent-marking behaviour between this marsupial species and commonly studied eutherian species, and the possible functional significance of scent-marking in M. domestica.     

Scent-marking by male mice under the risk of predation

The use by predators of scent marks made by potential prey isa largely unexplored potential cost of olfactory signaling.Here we investigate how animals that differ in their investmentin scent-marking respond to simulated predation risk, by comparingthe willingness to approach and counter-mark the scent marksof a competitor in the presence or absence of predator odor.We aimed to test whether animals that invest heavily in scent-marking,and which may thus be more vulnerable to eavesdropping predators,will either (1) take greater risks to counter-mark the competitor'sscent or (2) reduce or abandon scent-marking. Using outbredmale laboratory mice, Mus musculus, we show that, in the absenceof predators, individuals which initially scent-mark at highfrequency (high markers) approach the competitor's scent marksmore quickly and spend more time in counter-marking than thosewhich initially invest relatively little (low markers). Ina sib-sib experimental design, simulated presence of predationrisk (urine of ferrets, Mustela putorius furo) caused bothkinds of individual to approach the competitor's marks moreslowly, but high markers approached more quickly than low markersand spent more time in the vicinity of the competitor's marks.Only high markers significantly reduced their overmarking ofthe competitor's scent. These results suggest (1) that thereis a unique danger inherent to scent-marking at high frequenciesand (2) that high-marking males were prepared to accept increasedcosts of intrasexual competition in order to reduce the riskof predation. Further tests using the scent of naked mole-rats, Heterocephalus glaber, showed that these effects were not elicited simply by an unfamiliar odor. We discuss reasons for the observeddifference in response to predation risk between the groups,and the implications of these results for counter-selectionon scent-marking strategies.     

Field observations on scent-marking behaviour in saddle-back tamarins, Saguinus fuscicollis (Callitrichidae, Primates)

The scent-marking behaviour of a group of six saddle-back tamarins, Saguinus fuscicollis nigrifrons , was studied in the Amazon rain forest of north-eastern Peru. Three types of scent marking were recognized: anogenital marking, suprapubic marking and sternal marking. Anogenital marking was the most frequent type. Two or more scent-marking acts of the same or different type were generally combined into sequences. Most scent-marking was performed on branches and lianas; trunks were infrequently used. The tamarins mainly marked on horizontal or inclined substrata with diameters between 3 and 10 cm and a height between I and 10 m. The temporal distribution of scent-marking exhibited a maximum in the early morning between 06:00 and 07:00h and a minimum between 16:00 and 17:00h. The majority of scent-marking occurred in the peripheral areas of the home-range. The spatial distribution of scent-marking was correlated with the intensity of home-range use. No elevated frequencies of scent-marking were observed during intergroup encounters. The results of this field study are compared with findings from laboratory studies, and hypotheses concerning the function of scent-marking are discussed.     

Adult Male Scent-Marking in Lemur catta and Eulemur fulvus rufus

Scent-marking and olfactory communication are used extensively by prosimians and can provide spatial and temporal records of group movement and behavior. We compare rates of male scent-marking in relation to reproductive seasons, male dominance rank, and habitat use in two related prosimians: Lemur catta and Eulemur fulvus rufus. We collected scent-marking data on adult male Lemur catta at Beza-Mahafaly Reserve (dry forest), and on Eulemur fulvus rufus at Ranomafana National Park (rainforest), Madagascar. In Lemur, rates of overall scent-marking differed significantly by reproductive season, with higher rates occurring in mating and lactation/migration periods, whereas in Eulemur, reproductive season did not appear to affect scent-marking rates. Dominance rank of male Lemur catta did not affect rates of scent-marking. Among male Eulemur fulvus, dominance relations were not apparent; however, 2 of the 5 focal males scent-marked somewhat more frequently during the mating season and also experienced greater mating success. In Lemur catta, higher rates of scent-marking in the mating season may relate to indirect reproductive competition during a period of high aggression, while such mating competition was not as marked in Eulemur fulvus. Furthermore, higher rates of marking in resident male Lemur catta during male migration may correlate with vigilance toward immigrating males. Greater overall scent-marking rates in ring-tailed lemurs may relate to extensive intergroup home range overlap and no area of exclusive use, whereas the red-fronted lemur groups tended to forage in areas of their home range where little-to-no intergroup overlap occurred.     

Perinatal exposure to estradiol masculinizes aspects of sexually dimorphic behavior and morphology in gray short-tailed opossums (Monodelphis domestica)

The effects on adult sexually dimorphic behavior of perinatal exposure to estrogen were examined by treating male and female gray opossums with estradiol (EST), an estrogen receptor antagonist (tamoxifen:TX) or oil control (OIL) during the first week of life, a time period corresponding in this marsupial to late gestation in rodent species. Following gonadectomy and replacement therapy with testosterone in adulthood, males showed more scent-marking behavior than females and EST animals showed more scent marking than TX or OIL animals. Also, phalluses were longer and body weight was higher in males than in females and in EST-treated animals than in TX-treated animals; OIL animals were intermediate in these morphological measures. EST animals of both sexes showed less female-typical screeching threat behavior than OIL or TX animals. Because these hormone manipulations were conducted on the "fetus" directly in this marsupial (rather than via the maternal circulation as in previously studied eutherian species), these findings provide unique confirming evidence for masculinization of aspects of behavior and morphology by early exposure to estradiol in mammals.     

Sexual dimorphism in responses to unfamiliar intruders in the tamarin, Saguinus oedipus

Aspects of social structure in group-living species can be inferred by observing the responses of individuals to unfamiliar animals. This study examined the responses of mated pairs of cotton-top tamarins (Saguinus oedipus oedipus) to presentation of either unfamiliar conspecifics or members of a related tamarin species, the saddle-back tamarin (Saguinus fuscicollis fuscicollis). Male and female responses to intruders differed: resident males threatened, displayed piloerection, approached, and attacked intruders, especially males, while resident females showed increases in suprapubic scentmarking in the presence of intruders. Both males and females discriminated between the species of intruders, exhibiting more threats, scent-marking, piloerection, and approaches in the presence of conspecific intruders. There are pronounced sex differences in the signals and behaviour patterns that are elicited in an aggressive or territorial encounter with unfamiliar conspecifics in this monogamous primate.     

Diurnal Variation in Scent Marking Behavior in Captive Male and Female Common Marmosets,Callithrix jacchus

Chemical communication by scent-marking behavior in New World primates is used to prevent the access of potential competitors to a territory, to identify food resources and the reproductive condition of mates, among others. In common marmosets, primates of the Callitrichidae family, this behavior also occurs as olfactory identification of an individual or of the reproductive status of females. Despite this information, the diurnal variation and gender differences in the profile of this behavior remain to be investigated. The aims of this study were to establish the diurnal profile of the distribution of this behavior and the influence of the sex of markers. We used 18 adult common marmosets, Callithrix jacchus, 10 males and 8 females from 6 family groups (6 fathers and 4 sons; 4 mothers and 4 daughters). The frequency of scent-marking behavior was recorded for each animal over a period of 8 days, twice a week, for 4 weeks, starting when the animals left the nest box (approximately at 05:00 a.m.) until the end of the photophase, at about 05:00 p.m. A MANOVA test was performed to compare the frequency of scent-marking behavior at 2 hour intervals using pooled data for males and females. The results showed that significantly higher levels of scent-marking behavior occurred during the 03:00–05:00 p.m. interval compared to all other intervals. Lower values were recorded during the 11:00–13:00 interval and an effect of the sex factor was also found, with the values being higher for females than for males, although a significant difference was recorded only for the 07:00–09:00 interval. Minimal values for males were recorded during the 07:00–09:00 interval, whereas minimum values for females were recorded during the 11:00–13:00 interval. However, the highest values for both sexes continued to occur during the 15:00–17:00 interval. These results suggest that scent marking behavior in common marmosets has a preferential incidence at the end of the day and this might be occurring in association with feeding behavior. At this time these animals usually forage more to prepare for the night's fast. Since these animals can discriminate chemical clues as long as 24 hours after they have been left, the higher incidence of this behavior at this time probably will assure that the animals will localize feeding resources used on the preceding day. Significant elevation of scent marking behavior in females in relation to males was found only at 07:00–09:00 interval and seems to be associated with signalizing of reproductive status, preferential access to foraging or both.     

Scent-marking in captive red pandas (Ailurus fulgens)

Three male and three female captive red pandas (Ailurus fulgens) were observed during and outside of the breeding season to examine changes in scent-marking behavior. Variation in scent-marking was analyzed with respect to site preferences, sex differences, onset of breeding, behavioral correlates, and environmental factors. Both males and females exhibited significant preferences for particular marking sites, those being prominent points in the enclosures. Males showed significantly higher scent-marking frequencies than females, except in one enclosure where increased marking behavior was associated with the presence of young. Sexual dimorphism in the pattern of marking was also observed, with males showing a bidirectional mark and females a unidirectional mark. Female marking was greater during the breeding season. Sniffing and number of waddles per mark were associated with scent-marking. Temperature change was not related to frequency of scent-marking. These results are compared with scent-marking behaviors in other species of carnivores and functional explanations are suggested.     

Patterns of male scent-marking in Propithecus edwardsi of Ranomafana National Park, Madagascar

Scent-marking behavior has been well documented in many primate species. Three common functions attributed to scent-marking in males of multi-male/multi-female lemur species include: 1) advertisement of individual identity, 2) territorial defense, and 3) reproductive suppression. We examined the average number of scent-marks per hour exhibited daily by adult male sifakas (Propithecus edwardsi) and found that patterns of scent-marking changed with season, natal status, and dominance status. Males in single-male groups scent-marked at the highest rate, followed by dominant males, males of equal status, and subordinate males. Non-natal males generally scent-marked at higher rates than natal males, and adult males living in a natal group without a parent marked at higher rates than males living with a parent. All males scent-marked at higher rates in the migration season compared to the other seasons. These patterns were consistent with territorial defense and advertisement to females, and the suggestion that these chemical signals impart information concerning status. Since scent-marking behavior tracked seasons and varied with both dominance and natal status, it may serve multiple functions in males.     

Scent-marking in ring-tailed lemurs: Responses to the introduction of “foreign” scent in the home range

In three sets of experiments, a group of captive Ring-tailed lemurs ranging at liberty were presented with sticks scent-marked with their own scent, or with scent from unrelated animals or unmarked sticks. The results from experiments which involved a choice between scents indicated stronger responses, in terms of greater intensity of scent-marking to scent from “strange” animals. In the experiment where individual scents were presented one at a time, the length of time spent sniffing was greater for “strange” scent but this did not transfer to additional scent-marks. Most of the responses were elicited from males in the group and involved wrist-marking only, but timing of experiment influenced both responses and type of scent-mark probably in relation to the onset of oestrus. The role of scent-marking and the concept of group scent are also discussed.     

Diurnal Variation in Scent Marking Behavior in Captive Male and Female Common Marmosets, Callithrix jacchus

Chemical communication by scent-marking behavior in New World primates is used to prevent the access of potential competitors to a territory, to identify food resources and the reproductive condition of mates, among others. In common marmosets, primates of the Callitrichidae family, this behavior also occurs as olfactory identification of an individual or of the reproductive status of females. Despite this information, the diurnal variation and gender differences in the profile of this behavior remain to be investigated. The aims of this study were to establish the diurnal profile of the distribution of this behavior and the influence of the sex of markers. We used 18 adult common marmosets, Callithrix jacchus, 10 males and 8 females from 6 family groups (6 fathers and 4 sons; 4 mothers and 4 daughters). The frequency of scent-marking behavior was recorded for each animal over a period of 8 days, twice a week, for 4 weeks, starting when the animals left the nest box (approximately at 05:00 a.m.) until the end of the photophase, at about 05:00 p.m. A MANOVA test was performed to compare the frequency of scent-marking behavior at 2 hour intervals using pooled data for males and females. The results showed that significantly higher levels of scent-marking behavior occurred during the 03:00-05:00 p.m. interval compared to all other intervals. Lower values were recorded during the 11:00-13:00 interval and an effect of the sex factor was also found, with the values being higher for females than for males, although a significant difference was recorded only for the 07:00-09:00 interval. Minimal values for males were recorded during the 07:00-09:00 interval, whereas minimum values for females were recorded during the 11:00-13:00 interval. However, the highest values for both sexes continued to occur during the 15:00-17:00 interval. These results suggest that scent marking behavior in common marmosets has a preferential incidence at the end of the day and this might be occurring in association with feeding behavior. At this time these animals usually forage more to prepare for the night's fast. Since these animals can discriminate chemical clues as long as 24 hours after they have been left, the higher incidence of this behavior at this time probably will assure that the animals will localize feeding resources used on the preceding day. Significant elevation of scent marking behavior in females in relation to males was found only at 07:00-09:00 interval and seems to be associated with signalizing of reproductive status, preferential access to foraging or both.     

On the Relationship between Scent-Marking and Territoriality in Callitrichid Primates

Across a diverse range of animal groups, scent-marking is integrally related to the defense of territories and maintenance of social status. However, using data from a field study of wild saddleback tamarins (Saguinus fuscicollis), the authors of a recent paper claimed to find no evidence to support a relationship between scent-marking and territorial defense. Here I review the same evidence and argue that the data are consistent with the idea that scent-marking plays a critical role in territorial defense. This argument includes an attempt to clarify some misconceptions about the scent-marking mechanism that exist in the literature. I then reexamine the evidence in light of a proposed alternative function for scent-marking (that scent marks are used to explore reproductive opportunity and achieve extragroup copulations), and highlight some critical tests that could serve to distinguish between the two functional interpretations. Scent-marking could serve both in territorial signaling and in signaling to mates, but current evidence suggests that territorial defense is more, or at least equally, likely to be the primary function of scent-marking in callitrichids.     

Development of Olfactory Behavior in Captive Ring-Tailed Lemurs (Lemur catta)

We conducted a long-term research project (1996–1999) on developmental aspects of olfactory behavior in ring-tailed lemurs to document the ontogenetic sequence of olfactory behavior, including the possible presence of sexual differences, and the maturation of scent-marking. The subjects were a group of 18 lemurs housed in the Pistoia Zoo (Tuscany, Italy), which we observed during 1,735 h via all-occurrences sampling, scan-animal sampling and ad libitum sampling methods. We determined the time sequence of olfactory exploration and of scent-marking patterns, and investigated sexual differences in timing and frequency. We also followed the development of scent-marking through the juvenile and adolescent phases taking into account the two aspects of motor control and of the acquisition of social competence. On the whole, we found that olfactory investigation appears and matures earlier than scent-marking. Moreover, olfactory investigation of conspecifics appeared later than substrate exploration, and seemed to follow a sequence of increasing level of acceptance by the receiver. Social play is very important for the maturation of the gestural component of scent-marking. The olfactory behavioral pattern appeared to mature during the juvenile and adolescent phases. Although sexual maturation had obvious influence on the development of olfactory behavior, the onset of scent-marking patterns was only partially parallel to sexual maturation.     

Scent-marking and intrasexual competition in a cooperative carnivore with low reproductive skew

Most mammals scent-mark and a variety of hypotheses have been put forward to explain this behaviour. Differences in the main function of scent-marking between species are likely to be related to differences in social systems. Here, we investigate the functions of scent-marking in a cooperatively breeding carnivore. In the banded mongoose ( Mungos mungo ), individuals of both sexes commonly breed in their natal group and reproductive skew within groups is low. Using experimental scent-mark presentations, we tested predictions of the intrasexual competition, self-advertisement to potential mates and dominance assertion hypotheses. Both males and females responded more intensely to scent marks of same-sexed than of opposite-sexed individuals. Dominant individuals counter-marked more than subordinate ones and males showed higher counter-marking rates than females, but only marginally so. During oestrus, responses to scent marks were increased by both sexes. Our findings strongly indicate that scent-marking in the banded mongoose primarily serves a purpose in intrasexual competition both between and within groups. Unlike in other social herpestids and some solitary rodents, we found little evidence for self-advertisement. We suggest that the peculiar social system of the banded mongoose results in self-advertisement losing importance in this species, shifting the main function of scent-marking to intrasexual competition.     

Lack of gonadal control of the dorsal gland and sandbathing in male and female bannertail kangaroo rats (Dipodomys spectabilis)

Previous studies have demonstrated gonadal control of mammalian scent glands; castration leads to reduced scent-marking rates and smaller gland sizes. I investigated whether gonadal hormones control the size of the dorsal gland (a specialized sebaceous gland) and sandbathing as a scent-marking behavior in adult male and female bannertail kangaroo rats (Dipodomys spectabilis). Gland sizes of males and females were similar in all age classes, except adult males with larger body weights had proportionately larger glands than females. Male gland sizes declined 18% following castration but were not significantly smaller than those of intact males; females showed no change in dorsal gland size either as a result of ovariectomy or after estradiol benzoate implants. Sandbathing rates also did not decline as a result of gonadectomy. Rather, castrated males and overiectomized females sandbathed at higher frequencies than intact males and ovariectomized females with estradiol benzoate implants, respectively. Gonadal hormones apparently have little influence on the function of a specialized scent gland and may inhibit sandbathing as a scent-marking behavior in adult D. spectabilis.     

Scent-Marking of Giant Otter in the Southern Pantanal, Brazil

Giant otters live in social groups, consisting of a mating pair and one or two litters. Groups are territorial and mark their territories often with scent-marks. Our objectives were to evaluate the frequencies of marking and over-marking according to the social status of the individuals and to define the different postures used during the marking. We observed four groups, totaling 25 individuals (five alpha males, four alpha females, seven adult females, one adult male and eight juveniles) with group size ranging between four and 13 individuals. The study was conducted between July 2006 and July 2007 in the Vermelho River and in a stretch of the Miranda River, in the Southern Pantanal. We observed the groups for a total of 2006 min and recorded 95 events of marking totaling 84.9 min. Time spent marking varied between groups and ranged from 4.3 to 44.7 min. The alpha males marked more frequently (62% of marking events, 55 min) than the alpha females (17% of marking events, 13.6 min). Of the 59 events of scent-marking by the alpha males, 32 over-marked the marks of other individuals from the group. Of the 16 events of scent-marking of the alpha females, five over-marked that of other females from the same group. When scent-marking, alpha males used the 'stepping' posture most frequently (63%), then 'fore-paw rubbing' (24%), 'latrine use' (7%), and 'body rubbing' (6%). Alpha females used the 'stepping' posture most frequently (65%), then 'latrine use' (19%) and 'fore-paw rubbing' (12%), with only one event of 'body rubbing' observed during marking. Subordinate females used the 'stepping' posture (76%) and 'latrine use' (24%) during marking. Scent-marking can play many roles in mammals and for giant otters, and the main roles appear to be communication of social and sexual status and territorial defense.     

Sex differences in scent marking in Propithecus edwardsi of Ranomafana National Park, Madagascar

In this study we compared the scent-marking rates of females with those of males. Specifically, we examined the ability of season, dominance status, and natal status to explain the frequency of scent marking in female sifakas living wild in Ranomafana National Park, Madagascar, and compared the results with those published for males [Pochron et al., American Journal of Primatology, in press]. We also sought to determine whether vulnerability to infanticide affects marking frequency in adults of either sex, and whether female reproductive status affects female marking behavior. We found that males marked at twice the rate of females, and like males, females in single-female groups marked at the highest rates. Dominant females and non-natal females marked at higher rates than did subordinate females and natal females, a pattern also seen in males. This suggests that scent marks may convey important information about status. Neither females nor males varied their marking frequency with the presence of vulnerable infants. Females did not alter marking frequency with reproductive state, and like males, they marked at higher rates in the period prior to the mating season than they did in the mating season itself. This implies that females may use scent marks more for intrasexual aggression or territoriality than for mate attraction.     

Scent-marking behaviour in response to conspecific odours by the rat, Rattus norvegicus

The scent-marking behaviour of male and female rats in response to conspecific odours was investigated in two experiments. The results of the first experiment indicated that exposure to conspecific odours generally led to an increase in marking rates. However, no sex differences were found, and large differences in marking responses according to the sex of the odour donor were only found for dioestrous females. These results do not suggest that the primary function of scent-marking in this species is sexual. In the second experiment, odour sources differed not only in the sex of the donor, but also in their relative familiarity to the animal being tested. This experiment showed that males marked more in response to odours from familiar (non-related) females. Females did not differ significantly on measures of marking but did display greater interest in odours from unfamiliar males. The results are discussed in relation to possible functions of marking in this species.