Study of the Distribution of Mustelids over the Southern Urals Using Noninvasive Methods

1. What they did

The American mink was introduced to the Southern Urals and has spread, but how it is distributed there and how much it affects native mustelids had not been studied. Winter track counts work only in winter and are hard to use for rare species or in remote mountains. The authors combined several noninvasive methods to map mink and other small mustelids in the snow-free season.

• River bank surveys (2005 to 2010). They walked stretches of 1000 to 3000 m along the banks of 45 rivers and brooks, from May to November or December. They noted mustelid presence from footprints on the ground and from scats, recorded the type of bank, river bottom and bank vegetation, and marked each scat with a Global Positioning System (GPS) navigator.
• Scat identification. They collected 1090 scats and identified them by eye using published descriptions of the distinguishing traits of mustelid scats.
• DNA check. They tested 42 scats from 19 rivers and brooks with species-specific DNA markers, and compared the results with their visual identifications.
• Camera traps (autumn 2010). Four infrared cameras were set for 3 to 6 days at a time on five rivers, placed where scats had been found. Scats of tame ferrets were put in front of the cameras to attract animals.
• Interviews with rangers, hunters and local residents.

They grouped the rivers by channel width and tested which species favoured which type with a chi-square test.

2. What they found

Scats

• Of the 1090 scats, 987 (90.5%) were identified as American mink, 93 (8.5%) as common marten, 5 (0.5%) as otter and 5 (0.5%) as least weasel.
• Mink scats were found on the banks of almost all the rivers and brooks; marten signs on 24 of them.
• Of the 42 scats tested for DNA, 28 were mink, 12 marten and 2 otter. Two scats had been identified wrongly by eye; the authors give the visual error as 6.3% (see the detailed keywords for the numbers).

Where each species lived

• Mink favoured brooks flowing into larger rivers.
• Marten scats per km of bank were highest along forest brooks and rivers less than 3 m wide.
• The species tended to keep apart. On the Kabanka River, two scats downstream were otter, eleven upstream were mink, and a single marten scat was found near the headwaters. On some other rivers mink and marten scats were found on the same stretches, and on one brook both species used the same drainage pipes and marked there.

The 2010 drought

• Summer 2010 was abnormally dry. Most small and medium rivers dried up, the Miass River broke into isolated pools, and many otter and mink holes stood empty. Footprints did not hold on the dry ground.
• On the Malyi Syrostan River, which still held water and fish, one camera photographed least weasel, common marten, American mink, red fox and otter on the same stretch. Each species came at a different time of day (otter and red fox at night, marten at dawn, mink and least weasel in the afternoon). The authors link this crowding to animals moving in from dried-up pools.

Other species

• No polecat scats were found. Hunters said forest polecats had long been absent from the mountain–forest zone; local people recalled one attacking poultry in 2005, and polecats were reported near Muldashevo.
• From interviews and their own results, the least weasel is the most abundant of the other mustelids, though river valleys are not typical weasel habitat.
• Stoat prints were seen only once, near a beaver dam on the Atlyan headwaters.
• A camera recorded a Siberian weasel on the Atlyan; interviews say they are abundant in the forest–steppe zone.

3. What they concluded

• The American mink is now the most abundant and widespread mustelid in the Southern Urals, followed by the common marten, which prefers the upper reaches of mountain rivers and forest brooks.
• Mustelids along rivers normally keep apart in space. In extreme conditions several species share the same banks and avoid each other by being active at different times of day. Scat collection alone does not always show which species are in these groups.
• Any single method can distort results. Interviews show which species are present but rarely give information on rare ones. Scats show species, distribution, diet and exact places, but identification mistakes happen. DNA checks identification and measures visual error, but it is laborious, costly and needs a laboratory; species-specific markers are cheaper but need prior knowledge of the local fauna. Camera traps show which species are present and when they are active.
• The most complete picture comes from combining several noninvasive methods.

4. How tracking was or was not used

Tracks and signs were the core of the field survey. Mustelid presence along each river was recorded from footprints on the ground and from scats, and the scats were identified to species by eye using published descriptions. DNA analysis of a subsample was then used to check those identifications. Scats also guided where camera traps were placed. The authors note that footprints did not hold on dry ground during the 2010 drought, and that with footprint and scat surveys the accuracy depends on the researcher’s expertise, with error rates usually unknown. No trailing was reported.

5. Tracker or observer certification

Not reported. The paper does not say who identified the footprints and scats or what experience they had. This matters because the visual scat identifications (two out of 42 wrong when checked by DNA) underpin the distribution results.

6. Other technologies, skills or innovations

• DNA from scats stored in ethanol, tested with species-specific markers for five mustelid species and checked by sequencing.
• Reconyx infrared camera traps, which also recorded time, air temperature and moon phase.
• Scats of tame ferrets used as a lure in front of the cameras.
• GPS to record scat locations.

7. Implications for conservation (from the paper)

• Keeping biodiversity needs full knowledge of species, their relationships and their numbers, gathered with methods that disturb animals as little as possible.
• The introduced American mink has strongly affected native species, including mustelids, and led to the disappearance of the European mink. Less hunting, due to low demand for pelts, has also helped mink spread.
• Small mustelids are indicators of the state of the natural environment, and noninvasive methods are very promising for studying these secretive animals.