Scent marking by red foxes in Central Poland during the winter season

1. What they did

Scent marking helps mammals communicate with each other, and earlier studies of how red foxes mark with urine and scats had given contradictory results. Over several winters near Rogów in Central Poland, the author followed red fox trails in the snow to find out what objects foxes mark, how often they mark, how this changes through the winter, and where in their territories the marks are placed.

• Snow-tracking (mostly 1984 to 1988, November to March). Each fox trail was split into 250 m sections and drawn on a map. For each section the author recorded the freshness of the trail, carrion or food remains, hunting or attempts at hunting, urine and scat marks, and the number of other fox and rodent trails crossing it.
• Marked objects. For 1940 urine marks and 203 scats, the author noted exactly what had been marked, and grouped the objects by how long they would hold scent: permanent (such as tree trunks, stumps, stones, burrows and clods), undurable (such as flat snow, grasses, weeds and hunting sites) and intermediate (shrubs and saplings).
• Territories. Earlier work in the same area had mapped the territories of four fox families and found them stable over four winters. The area was divided into 400 × 400 m squares, and marking intensity was calculated per square, both per km of trail and per hectare per 24 hours.
• Sex differences. In more than ten cases, the sex of the fox could be told from where the urine landed on the trail, so marking by males and females could be compared.

2. What they found

What foxes marked

• In the forest, foxes most often put urine on tree trunks and stumps, shrubs, fallen twigs and sticks, and flat snow. In fields, most urine marks were on cultivated plants and weeds, balks and the tops of clods.
• 70 to 80% of urine marks were on things raised above the ground; on average 13% were on flat snow. Scats were placed on flat snow far more often (the text says 60% of cases), and also at kill sites and on or near carrion.
• Short-lived objects, which hold scent only until the next thaw or snowfall, made up about half of all marks (47% in forest, 55% in fields). Permanent objects made up 34 to 42%, and intermediate ones 19% in forest and 4% in fields.
• Foxes also marked new objects in their range: old gloves and plastic bags left by forest workers, and rodent traps.

Hunting sites and carrion

• The author recorded 240 digs in the snow where foxes tried to catch rodents, about 3 per km of trail. Only 26 could be confirmed as successful, from bits of fur or drops of blood. Urine marks were left at a similar rate at successful digs (3 of 26) and digs with an unknown result (29 of 214), and digs were rarely marked with scat (3 times). Most sites of successful hunts were left unmarked.
• Small insectivores caught by foxes were found on the trails (12 shrews, a mole and a water shrew); only 3 had been partly eaten, and only one was urine marked.
• Of 105 larger prey items and carrion (dead roe deer, hares, dogs and other domestic animals), 34 were marked with urine and 24 with scat. Scats built up near the carcasses of roe deer and dogs that foxes fed on over time. Some carrion, mainly hens and bones of domestic animals, was visited without being eaten or marked.

How often foxes marked

• On average foxes left 4.41 urine marks and 0.35 scats per km of trail.
• Scat marking dropped at the start of winter (November and December) and in the first ten days of February.
• In the forest, urine marking rose in the second half of winter (after 15 January), from 3.56 to 4.99 marks per km. In fields it stayed about the same all winter. Over the second half of winter, forest trails were marked more than field trails (4.99 and 3.85 marks per km); over the whole winter the difference was not significant.
• Males (trailed for 34.3 km) left 5.7 urine marks per km and females (23.3 km) 4.2; scats were 0.39 and 0.56 per km. These distances were too short for statistical testing.
• Males put more of their urine marks on permanent objects than females (50.3% versus 14.1%). Females marked flat snow more often than males.

Marks across the territories

• Marking per square varied widely, from 1 to 8.7 urine marks and 0 to 1.95 scats per km of trail.
• Squares at territory borders, and where two family territories overlapped, were marked about as much as squares inside territories. Areas of very heavy marking were found as often in the centre as at the borders.
• Marking was not related to how much foxes searched an area, or to the number of fox shelters and burrows. It was weakly related to rodent activity: fox trails through areas with many rodents were marked more often.
• Combining these data with earlier work, the author estimated that a fox makes about 44 attacks on voles and mice per 24 hours and catches about 6.7, a hunting success of about 16%.

3. What they concluded

• Foxes use whatever objects are common in their habitat, but the frequent marking of short-lived objects stands out. Marking new objects may be a way of getting to know new things in the habitat, which also marks the territory.
• Raised objects probably spread the scent further. The finding that scats were mostly left on flat snow goes against the view that predators place scats on conspicuous objects.
• The marking at kill sites and carrion did not support Henry’s (1977) idea that foxes mark places where food has been eaten but the smell remains, so as not to search them again. Foxes seemed to urinate mainly at places with an attractive smell, and many marks where rodents are plentiful might lead foxes to search those areas harder.
• Marking rates may be slightly underestimated, because urine smell on snow-free trunks may come from earlier visits and cannot be dated.
• Fewer scats early in winter probably reflect less food: the first snow makes rodent hunting harder, hares are in good condition and there is little roe deer or wild boar carrion. The drop in early February matched the rut, when males may eat less while searching for mates.
• The rise in urine marking in the forest late in winter may be due to the rut, but it continued after the rut and did not happen in the fields. The author suggests foxes may mark around their future den as birth approaches, and that after mating these marks may help defend the territory.
• Urine seems more important than scats in fox scent communication.
• The results give no clear answer on whether scent marking defends territories. Scent marking may only support calls and visual signals. Specially designed field experiments are needed, because simple field observations of marking will not answer the question.

4. How tracking was or was not used

The whole study rests on snow-tracking. Fox trails were followed in the snow, mapped in 250 m sections, and read for urine marks, scats, digs where foxes tried to catch rodents, kill sites, carrion and food remains. Bits of fur and drops of blood at digs showed which hunts had succeeded. The sex of a fox was told from where its urine lay in relation to the trail. Fox and rodent trails crossing each section were counted to give an index of how intensively each area was searched. The author also notes a limit of reading signs: fox urine smell, which people can detect for a few days, cannot be dated precisely, so a smell on a trunk may be from an earlier visit.

5. Tracker or observer certification

Not reported. The paper does not say who did the snow-tracking or how their skill was checked, although all the results depend on finding and identifying urine marks, scats and hunting signs, and on telling the sex of foxes from their urine.

6. Other technologies, skills or innovations

• Indices that turn trail records into marking rates per km of trail and per hectare per 24 hours, using a modified formula of Priklonski (1965).
• A grid of 400 × 400 m squares laid over mapped fox territories to show where marks were concentrated.
• Sorting marked objects by how long they would hold scent (permanent, undurable, intermediate).