Field Guide for Aging Tigers

Dr. Y V Jhala & Dr. Ayan Sadhu

Introduction

We have developed a new method for estimating the age of wild tigers in the field. In the past, experts have used a variety of physical characteristics, such as tooth colour and wear, body size, and nose pigmentation, to determine a tiger’s age. However, there was no established method for doing so. So, we created our own method based on our observations of wild tigers and close inspections of more than 20 captured tigers, whose ages were already known.

Our Approach

Our technique involves looking at the tiger's body size, body characteristics, teeth eruption, wear and coloration, gum line recession, and nose pigmentation to determine its age and place it in one of six categories: cubs (less than 12 months), juveniles (1-2 years), sub-adults (2-3 years), young-adults (3-5 years), prime-adults (5-10 years), and old-adults (over 10 years).

Tigers often yawn when in proximity to people in a non-confrontational manner, as a means to intimidate. This helps to closely observe teeth condition and gum-line recession with binoculars or telelens photographs. Teeth eruption, wear and coloration as well as gum line recession are highly correlated with the age of the tiger.

Cubs

(<12 months)

Juveniles

(1-2 years)

Sub Adults

(2-3 years)

Young Adults

(3-5 years)

Prime Adults

(5-10 years)

Old Adults

(>10 years)

Cubs (<12 months)

Cubs were usually observed after they were about 2 months old. At this time, they rarely accompany their mother and are restricted to birth site. By 5-6 months age they reach the belly of their mothers and accompany to nearby kills. By the age of 6-8 months there is a distinct size difference between male and female cubs (fig. s1d).

Juveniles (1 to 2 years)

Juvenile tigers accompany their mothers to larger kills and are usually not photographed alone, making size comparison easy (fig S2a, S2b). Male tigers show faster growth than females and are seen to be substantially larger.

Sub Adults (2 to 3 years)

At the sub-adult stage, the males are substantially larger than the females. Often sub-adult tigers move around with their siblings, but by 30 months they become more solitary. The body is almost as large as adults and can no longer be used for size comparisons as most of the camera trap images are of solitary tigers. A prominent ridgeline on the inner side of the canines and a groove on the outer edge of the canines is clearly visible (fig. s3c, s3d). Facial hair in the form of a short mane below the lower jaw/cheek is usally seen even in camera trapped photos of males.

Young Adults (3 to 5 years)

By 3 years most tigers are close to full adult size (fig. s4a, s4b), but continue to accumulate weight upto 4-4.5 years of age.

Pregnant & lactating tigers : A heavily pregnant tigress (fig. s4e) can be distinguished from a fully fed tigress by the visibility of prominent teats and udders. After birth, the belly is normal with full udders where nipples show signs of intense suckling (fig. s4f). For un-bred females and early days following first births the nipples are pink in color (fig. s4g) and become pigmented, darkened grey and keratinised after cubs suckle intensely.

Prime Adults (5 to 10 years)

Careful inspection shows a receding gum line on canines, making the canines appear larger (fig. s5d). The canine ridge is amlost indiscernible, and the grove is highly worn out (fig. s5c).

Old Adults (>10 years)

Body condition of tigers is usually not a good parameter to use for ageing. Often very oldtigers that have lost their canines can be in poor condition (fig. S7a) but can regain condition withjust a couple of good meals (fig. S7b).

We believe that by using the criteria described above an experienced researcher can age anadult tiger to its stage accurately with an error margin of about a year, and younger tigers(sub-adults and juvenile) to about 3-4 months. Cubs can be aged with the accuracy of about amonth by field observations.