Population and Distribution:
The Siberian, or Amur tiger (Panthera tigris altaica), is the northernmost sub-species of tiger in the world today. About 350-400 adults and 100 cubs are found in Primorsky Krai and southern Khabarovsky Krai in the Russian Far East, and another 15-20 individuals live in forests near the Russian border in Northeast China. Today the Amur tiger is confined to a fragment of its former range – at one time this cat lived throughout the Russian Far East, the Korean Peninsula and Northeast China, stretching even into Northeast Mongolia.
At the end of the 1800s, up to 150 tigers were legally killed each year in Russia, although this number dropped to around 50 per year in the early 1900s, due to declining populations. The first range-wide Amur tiger survey was organized by Lev Kaplanov at the end of the 1930s. At that time Kaplanov and his team estimated that only 20-30 individuals remained.
Kaplanov’s work was important in bringing a ban on tiger hunting in 1947. However, capture of cubs for zoos continued to limit population growth until an initial capture ban, and then limitations on captures for zoos were put in place. It took Amur tigers another 45 years to recover from critically low population levels.
Amur tigers are often considered the largest of the tiger sub-species, although they are in fact about the same size as the Bengal tiger. An adult male usually reaches a body length of 2 meters, with his tail adding another meter. Average weight for males is 160-190 kg, while females are smaller, weighing in at 110-130 kg. The largest male captured for scientific research under the Siberian Tiger Project weighed in at 206 kg. Males, females and cubs can be distinguished by their tracks: a male’s paw pad measures 10.5 – 14.5 cm across, a female’s – 8.5 – 9.5. cm, and a cub’s – from 5.5. to 10 cm. (Male cubs, after one year, usually have paw measurements already larger than their mothers’.)
Amur tigers’ coloring can be somewhat lighter than that of other tigers, especially in winter, and their fur is orange or light orange. Some people mistakenly think that Amur tigers have white fur. White fur is actually a recessive genetic trait in Bengal tigers, and all white tigers in captivity today are decedents of a single white Bengal tiger taken from the wild in India.
Reproduction and Life Span:
The oldest Amur tigers in zoos have lived to 35 years of age, but 14 years is the oldest known age for an Amur tiger in the wild. (Olga, the first tiger captured as part of the Siberian Tiger Project, was 14 years old when she was killed by poachers.) Tigers can reproduce starting at around 3 years of age, and mate at any time of year. Gestation is 3 – 3 ½ months and most cubs are born in summer and fall, but cubs can be born in the dead of winter. Surprisingly, tigers often do not give birth in a den, but simply on the ground in dense, brushy areas. However, they choose rocky areas with lots of nooks and crannies where cubs can hide once they become mobile. Mothers will move cubs if they think there is a chance of danger and frequently do so after cubs are about 1.5 months old. Tigresses usually leave their cubs behind while hunting, but begin taking them to kills when they reach about 3 months in age. Litter sizes are between one and five cubs, and due to disease, hunger, congenital defects, and predation, approximately 50% of cubs die in their first year.
Figure 1. Birth dates have been identified for 27 litters of tiger cubs by staff of the Siberian Tiger Project, with births occurring in every month but January and March. Later summer and early fall is the peak of birthing.
Tigers are territorial, and although female tigers may divide their home ranges with their daughters, male tigers leave their mothers to find their own territory, usually when they are between 16 and 22 months old, and sometimes travel hundreds of kilometers in search of a vacant area. Research conducted under the Siberian Tiger Project has demonstrated that resident female tigers need 250-450 km² to successfully rear cubs. Males’ territory can be up to 2000 km² and overlap with several female territories.
Figure 2. Home ranges of 5 adult resident female tigers, based on data from 1993 to 1997. Overlap between females is low because they defend their territories from each other, ensuring sufficient food will be available to raise young.
Tigers mark their territory by rubbing against trees – sometimes leaving hairs behind – and spraying urine on trees and rocks. They paw and scratch the forest floor as well, leaving large scrape marks 40-70 cm long and 20-30 cm wide. These “scrapes” are usually augmented with scat, anal gland secretions, or urine.
The Amur tiger inhabits boreal and temperate mixed (deciduous broadleaf and coniferous-deciduous broadleaf) forests in the southern Russian Far East and Northeast China. WCS research under the Siberian Tiger Project has demonstrated that presence of prey – particularly wild boar and deer – is the most important factor determining tigers’ distribution. Northernmost distribution of tigers is closely tied to northernmost distribution of red deer and wild boar, and the Korean pine-deciduous forests that these prey need to survive.
Figure 3. The historical northern distribution of tigers (derived from Heptner and Sludski 1973) closely mirrors the northern distribution of the Korean pine and deciduous forests that define the “Ussuriisk taiga,” that is, the forests of this region of the Russian Far East.
Red deer, wild boar and sika deer, and roe deer make up about 80-90% of tiger prey across tiger range, with smaller animals such as badgers and raccoons, and larger animals such as black and even brown bears being occasionally taken during the summer months. One radio-collared tiger studied by WCS ate more bears than anything else, at least during the summer months. Tigers sometimes prey on domestic animals (particularly if there is little prey available in the forest), including dogs and livestock (cows, horses), which leads to conflicts between humans and this big cat. When chasing prey, tigers can run at speeds up to 20 meters per second for short distances. Although Amur tigers may cache their kills and return to eat more later, they do not bury their kills with leaves or snow. Prey species occur at naturally low densities in the Russian Far East, meaning that tiger densities here are lower than in other tiger-range countries, and that tigers need a much larger territory (see home range, above) in order to find enough prey to survive.