Some Observations and Field Experiments on the Urine Marking Behaviour of the Red Fox, Vulpes vulpes L.

1. What they did

Wild red foxes often urinate very frequently on conspicuous objects, in brief “token” marks, yet at other times go hours without urinating. The author set out to learn where, when and why foxes make these marks.

Because a wide-ranging animal like the fox cannot be studied well in a laboratory, he hand-reared fox cubs and trained them to walk on a leash from 8 weeks old. The foxes chose their own routes, day after day, through a study area of about 20 ha near Oxford, England, roughly the size of a small wild fox territory. He then checked his ideas against wild foxes, watched with infrared binoculars, at Boars Hill, Oxford, and at Ein Gedi, Israel.

• Following development. He recorded how seven vixens began to mark as they grew up (1974 to 1977).
• Mapping every mark. For two vixens (Vixen I and her daughter Vixen II) every site urinated on was marked with a numbered stake and reflective paper, giving the history of 2615 token-marked sites. Over 112 walks of about an hour (November 1974 to March 1975) Vixen I marked 615 separate sites.
• Field experiments. He sprinkled urine from dead foxes on sites inside and outside the vixen’s marking range, dug up favourite marking tussocks and moved them back and forth across her border, laid out heaps of straw smelling of her own urine, and placed urine from strange vixens near the point where she usually turned back.
• Caching trials. He offered mice to Vixen I inside and outside her marking range and noted where she carried them to cache them.
• Social status. He watched marking in two captive family groups, two tame released vixens with radio collars, and wild family groups.

2. What they found

How marking develops

• Young vixens only squatted to urinate (7 to 25 seconds) until they were about 5 to 6 months old. Then they began token marking: brief sprinkles of a few drops on conspicuous sites such as grass tussocks, after much sniffing.
• Until about 14 weeks old, vixens reacted to wild fox urine with submissive behaviour, as if greeting an adult fox.
• Two leash-walked dog-foxes did not token mark until about 10 months old. They then marked about once a minute for a few weeks and over-marked every token of the dominant vixens.

Where marks are placed

• Marks were mostly along the network of paths the foxes used. The more often a path was walked, the more it was marked.
• On a garden path with fewer but more conspicuous sites (a lavender bush, an Antirrhinum, a Hydrangea), each site was marked more often, so the path received the same number of marks per metre as nearby rough grass.
• Marking was much lower on clods in an open ploughed field than along its edge path.
• Half of all 615 sites Vixen I ever marked had been marked within the first 18 days. Some sites were marked for over 5 years, and the vixens made detours to “top up” favourite sites.
• Within her marking range Vixen I marked at least once a minute, often four times a minute, everywhere she went.

The edge of the marking range

• Over the outermost 200 m of her range, marking faded away, and beyond one site she never marked at all, although she still sniffed at likely sites.
• All 13 urine-treated sites inside her range were marked; none of the three outside were.
• Two transplanted tussocks were marked on all 35 trials inside her range and on none of 22 trials outside it. The line between marking and not marking was no more than 20 m wide.
• Straw heaps were marked 28 of 31 times in the woodland, 14 of 23 times in a field corner, and once in 20 on the outer field border.

Reaction to strange urine

• When urine from a strange vixen was placed beyond her usual turning point, Vixen I sniffed it, wheeled around and went back into her range. When the urine was moved closer, she turned back at the new spot. Her own urine placed in the same places did not change her turning point.

Changes over time

• Vixen II, who was subordinate, at first marked over a wider area than her mother, but by spring her range shrank to the same borders. Vixen I bred; Vixen II did not.
• In September 1975 and 1976 Vixen I’s border seemed to break down for a while: on one walk 64.5% of her marks were outside her usual range, and two days later 75.0%.

Wild foxes

• At Ein Gedi, marks by members of two neighbouring family groups did not overlap and followed the territory border found by radio tracking and observed encounters. No foxes marked during ten observed trips into a neighbour’s territory.

Food caching

• Of 29 mice Vixen I found outside her marking range, 75.8% were carried up to 100 m back towards or into her range and cached there. Mice found inside her range were carried in all directions.
• Wild foxes at Ein Gedi made 112 observed caches and carried food back into their own group’s territory to cache it.

Social status

• In general, subordinate vixens token marked less than dominant ones. In one captive group only the dominant vixen token marked, and when dominance changed hands, so did the marking. Victors in fights marked heavily for 1 to 2 minutes afterwards.
• Dominant foxes sometimes marked sleeping subordinates on the head or shoulder (allomarking).

Other scent marking

• In winter, foxes rubbed their chins and the sides of the mouth on saplings and hedges, sometimes dragging branches through the angle of the jaw (“mouthing”). Enlarged glands were found there.
• Of 135 scats Vixen I left during 112 walks, at least 95 (70.3%) were on sites she had already urine marked.

3. What they concluded

• Allowing for small samples and the leash-walking method, the results support the idea that the area a fox token marks corresponds to a territory, and that token marking helps organise how foxes space themselves.
• Turning a vixen back with strange urine directly shows that foreign marks can deter a fox, which earlier wolf studies could show only indirectly.
• A vixen could tell her own urine from that of other foxes, and remembered the positions of many marking sites.
• Urine marking probably serves many purposes, from keeping territories to courtship, and occurs in fights, allomarking and alongside other scent marks. Why foxes mark so many sites so often is still unexplained.
• The main limitations were the lack of direct border encounters with other foxes and the uncontrolled presence of wild foxes in the study area.

4. How tracking was or was not used

Tracking played a small part. One wild dog-fox was tracked across snow in April and found to have urinated 14 times in 200 m, and the author notes that snow tracking sometimes reveals marking rates in wild foxes comparable to those of the leash-walked foxes. In a footnote he describes the yellow, withered leaves of habitually marked plants as a useful field sign when tracking wild foxes. Most data came from direct observation of tame foxes on the leash and wild foxes through infrared binoculars, with radio tracking used to map wild territories.

5. Tracker or observer certification

Not reported. The paper does not say who did the snow tracking; the observations are reported in the author’s voice.

6. Other technologies, skills or innovations

• Leash-walking hand-reared foxes so that marking could be watched closely and tested by experiment in natural surroundings.
• Numbered stakes with reflective paper to record every marking site, including at night.
• Field experiments: transplanted tussocks, urine samples from other foxes, and straw heaps smelling of the vixen’s own urine.
• Infrared binoculars for watching wild foxes at night, and radio collars on wild foxes and on released tame vixens.