Morphometrics of the Tracks of Puma concolor: Is It Possible to Differentiate the Sexes Using Measurements from Captive Animals?

1. What they did

Pumas are secretive and hard to see, so tracks are a useful way to learn where they are and how many there are. Being able to tell males from females by their tracks would let researchers estimate sex ratios, which matter for understanding population dynamics. Earlier puma track studies had mostly tried to identify individuals, not sexes.

The researchers collected tracks from 8 adult pumas of known sex (4 males and 4 females) at two zoos in Chile, by leaving trays of clay on the cage floor. They used only front tracks and photographed each one with a digital camera. They then compared male and female tracks in two ways:

• Measurements. On the photographs they measured 13 features: the angle between two toes, the outer toe spread, the heel to lead toe length, the heel pad width, the area of each of the four toes and of the heel pad, the length of the 2nd and 3rd toes, and the total length and width of the track. Left and right tracks were analysed together.
• Shape. They traced the outline of the heel pad and described its shape mathematically (elliptical Fourier analysis), which looks at shape independent of size.

For both, they tested for differences between the sexes and used discriminant analysis to find which features best separated them and how many tracks would be assigned to the right sex.

2. What they found

• They obtained 38 tracks: 17 from males and 21 from females.
• Male tracks were larger for most measurements. The area of the inner toe, the area of the outer toe, and the lengths of the 2nd and 3rd toes did not differ between the sexes.
• Mean total length was 9.18 cm for males and 8.13 cm for females; mean total width was 8.54 cm and 7.36 cm.
• The measurements separated males from females. The features that best told them apart were the heel pad width, the area of the inner toe, the area of the 2nd toe and the area of the heel pad.
• Heel pad shape also separated the sexes: male heel pads were relatively narrow in the middle, while female heel pads were broader there.
• 88% of male tracks and 100% of female tracks were assigned to the correct sex.
• The tracks (mean 8.7 cm long and 7.9 cm wide, as given in the discussion) were larger than those reported in an earlier study of Chilean pumas (6.7 cm long and 6.8 cm wide), which included juveniles and could not tell the sexes apart.

3. What they concluded

• The differences between male and female tracks match the size difference between the sexes: male pumas are larger and heavier.
• Their best measures partly agree with earlier studies on identifying individual pumas (outer toe spread and heel pad width), though other studies found different measures most useful.
• This was the first use of heel pad shape analysis in this kind of study, so what the shape difference means is not yet clear.
• Identifying the sex of pumas from their tracks may be possible with these techniques, but the approach needs wider testing. Robust methods for identifying individuals from tracks have not yet been developed.
• A larger sample of wild pumas is needed. In the field, soil type matters: fine soils such as clay or dust show the edges of a track clearly, while coarser soils such as sand make measurements less precise. The time of day of photographs can also cause errors, because the light direction changes.

4. How tracking was or was not used

No field tracking was done. Tracks of known animals were collected in clay trays in zoo cages, photographed, and measured on the photographs. The study tests whether track measurements and heel pad shape can show an animal’s sex.

6. Other technologies, skills or innovations

• Digital photographs of tracks measured with image analysis software (ImageJ).
• Geometric morphometrics: heel pad outlines traced with tpsDig and analysed with elliptical Fourier analysis, which compares shape without the influence of size.

7. Implications for conservation (from the paper)

• Knowing the sex of animals from their tracks would help estimate sex ratios and relate them to population dynamics and home ranges, which is relevant to protection plans for pumas and other species.