Squirrel Behaviour - Scent-marking

There is very little information on the role of scent in squirrel society and most that does exist is based on relatively few observations of Grey or Fox squirrels. Squirrels appear to have a highly developed sense of smell, and several authors have suggested that scent is of critical importance when communicating with other squirrels, particularly when marking out a territory and during the breeding season. Indeed, in The Natural History of Squirrels, John Gurnell notes:

Olfactory communication is used more than many people realise, and, for example, squirrels leave scent marks throughout the home range for other squirrels to find.”

A male Grey squirrel (Sciurus carolinensis) sniffing the scent trail left by a female in January 2018. Female squirrels are in season for only one day and attract a lot of male attention as the time approaches. - Credit: Caroline Boxall.

There are very few data on the marking behaviour of Grey squirrels, and virtually nothing on that of the Red. As such, we know surprisingly little about the information contained within these scent marks, or how quickly they degrade; but they are thought to convey information about the sex, social status and reproductive condition of the depositor. Vaginal secretions ‘posted’ in the female’s home range during the breeding season may also give males an idea of which females are in oestrous. Certainly, during the breeding season females appear to scent-mark much more frequently, rubbing their cheeks and anus on branches, gnawing bark and squirting (hormone-laden?) urine around. Patches of gnawed bark may be a visual clue to the make the marking site more obvious to passing squirrels, or may be an attempt to remove scent from a previous visitor.

Both sexes have a number of apocrine glands in the skin around their mouths and this ‘cheek-rubbing’ or ‘face-wipe’ behaviour is thought to be a way of depositing scent from them. In his 1993 paper to the Journal of Zoology, John Koprowski made the distinction between what he called “marking point visitation” (MP) and cheek-rubbing (CR) in Grey squirrels. CR was an activity that all squirrels engaged in, regardless of sex and age and involved the sporadic rubbing of cheeks on branches as they transverse their home range – these ‘rubbings’ took less than two seconds per bout. MP, by contrast, was almost exclusively carried out by adult males and was much more involved. Koproswki explains that it is a:

slow, deliberate approach while sniffing with the tail raised over the body, followed by vigorous gnawing without ingestion of bark, and repeated rubbing of the cheeks and chin against the gnawed area

Squirrels will rub their faces on branches and trunks, depositing scent from glands around their mouth. They will sometimes also spread themselves out on the branch and inch their way along, depositing body scent over a wider area, as this Grey squirrel (Sciurus carolinensis) is doing. - Credit: Marc Baldwin

Each MP incidence could last more than 30 seconds and the suggestion is that CR is more about self-orientation within the habitat, while MP is a message for other squirrels.

While at Silwood Park in Berkshire during the 1960s, Ministry of Agriculture biologist Jan Taylor studied the marking behaviour of Grey squirrels and published a couple of short papers with her findings in the Journal of Zoology; one in 1968 and a second in 1970. Taylor noted that squirrels would gnaw areas of bark away and urinate on the stripped part of the tree such that:

regularly used patches, usually located under branches or in root hollows, often acquire a dark, strong-smelling stain below the gnawed area.

A female Grey squirrel (Sciurus carolinensis) stopping to deposit a scent mark from her genitals during a mating chase. The male will subsequently sniff at this mark for several seconds, assessing how close she is to estrus. - Credit: Marc Baldwin

It seems that the squirrels must spray a jet of urine at right-angles to the body in order to mark these sites on the underside of branches and tree protuberances. Apparently, despite standing several inches away, Taylor was frequently “marked” by tame squirrels climbing cage netting, suggesting a reasonably powerful jet can be produced. During the course of her studies, from 1964 to 1969, Greys were seen at marking points on 32 occasions, with the peak of activity during January and May, which coincides with the bimodal breeding season. Very few observations were recorded between July and November, although other observers have seen squirrels visiting marking points throughout year. Taylor concluded:

The use by females … may be territorial in nature and/or for indicating the presence of a female approaching, or in, oestrus. Males may use them to indicate to others that a potent high ranking male is present, or has visited the area, while all animals could be involved in using them to advertise that the woodland is occupied by resident animals.”

Taylor also observed the squirrels squat marking after rubbing themselves on the branch near well-used marking stations:

As females left the marking points they sometimes crawled over them in such a way as to suggest that they squirted them with urine, but this was not confirmed.”

A Grey squirrel (Sciurus carolinensis) scent-marking a branch. Chin rubbing is a well-documented behaviour in squirrels. Several authors have inferred the presence of scent glands in the chin or sides of mouth based on the behaviour, but they've never been demonstrated histologically. - Credit: Adele Brand

If you watch a squirrel grooming (see Hair types & grooming), you’ll notice the front paws are frequently drawn over the face and around the mouth – this may help collect scent and distribute it over the squirrel’s body.