|
Why captive Bengals are smaller than Wild Bengals?
|
 (11-10-2019, 04:47 AM)Roflcopters Wrote: It’s a combination of things, environment and surrounding are two of the biggest factors. for example, if those specimens were from the wild. a lot of us would have mistaken them for females or young sub-adults. they’re definitely nowhere near their wild cousins. in the wild, a tiger generally can do a lot better in the summer seasons and even then we see a few tigers that don’t retain their overall body-mass that they would normally have in the spring, fall or winter. Sangam from Kanha for example was skin and bones in the summer, the same male in any other season was considerably a lot bulkier. in the wild, they have the luxury to go and explore. plenty of water bodies for them to go around. in captivity, options are very limited and summer in India is generally very brutal. which puts them at a significant disadvantage, also remember tigers position themselves according to their environment. another example, T24 aka Ustaad of Ranthambore. when he was in the wild, he weighed 240kg on a 250kg capacity scale. same male in captivity was just a little over 200kg, 215kg to be exact. my friend who recently saw him thought he would be lucky if he weighed over 200kg now. 1- AMUR TIGERS Most captive Amur tigers in European zoos are descendants of wild Amur tigers captured and moved to Europe in the period 1945-1970. This is in particular true for zoos located in countries occupied by the former Sovjet-Union (during and) after the Second World War. Although wild Amur tigers were severely threatened in the period 1900-1950, large individuals were not uncommon in that period. In fact, there are many records of large males shot in that period in particular. According to those who went over historical records (referring to a chapter in a document on the ecology of the Amur tiger published in 2005), Amur tigers declined in size after 1970 or thereabout. If both observations (large Amur tigers in the period 1900-1950 and a decline in size after 1970) are true, chances are it could, and maybe should, show in the size of captive Amur tigers in European zoos. The reason is these tigers are descendants of wild Amur tigers captured and moved to Europe in the period 1950-1970. A former member of AVA, 'Eagle Raptor', had information about 16 captive male Amur tigers in European zoos. In August 2008, in the thread 'Tigers I look after, plus Stud book numbers, weights, pics', he wrote they ranged between 400-600 pounds roughly. Most of them were 480-500 pounds (217,78-226,80 kg.). If we compare them to the 10 wild males captured before 2005 (referring to the same document on the ecology of the Amur tiger I referred to above), the conclusion is these captive males in European zoos outweighed their wild relatives by about 100 pounds. Based on what I have (referring to the captive male Amurs I measured as well as reliable information from European zoos), I'd say captive male Amur tigers also were longer (and taller) than their wild relatives. In the sixties and seventies of the last century, I saw captive male Amur tigers significantly larger than those seen in zoos today. V. Mazak is one of the few who measured a number of captive male Amur tigers in European zoos in the sixties of the previous century. His information on total length, weight and the actual standing height at the shoulder in his great book 'Der Tiger' (third edition, pp. 179-190) more or less confirms what I saw. All in all, one could conclude captive male Amur tigers in European zoos and facilities were both larger and heavier than their wild relatives in the period after, say, 1970. As all captive males were descendants of wild Amur tigers captured in the period 1950-1970, the observation on the decline of wild Amur tigers after 1970 could have been correct. Although wild Amur tigers today seem to be a bit larger than a few decades ago, the question is if they will be able to get close to the model produced a century ago. My guess is it will take time. In my opinion, the reason isn't prey depletion, but gene depletion. If I was involved in the STP (Siberian Tiger Project), I would start a project on the essentials of captive Amur tigers right away. My guess is the findings could be surprising. The next step could be to reintroduce lost genes. According to 'Eagle Raptor', all captive Amur tigers are descendants of at least 119 wildcaught founders (referring to the situation in 2007). Cubs caught after 2000 are not included. In 2007, about 600 descendants of wild Amur tigers lived in zoos and facilities. 2 - INDIAN TIGERS In his post of August 2008, Eagle Raptor said there were about 210 captive Indian tigers in 2007. These tigers were descendants of 29 wildcaught founders. Compared to Amur tigers, therefore, the number of founders was rather limited. I'm not saying the limited number of founders could have had an an effect on the size of captive Indian tigers, but it is a fact (referring to both old records and recent research) that India has distinct sub-populations. The question is if the 29 founders represent all sub-populations. Sizewise, the answer to this question is important. What I have suggests there could be significant differences in size between these sub-populations. Indian tigers, unlike their relatives in Russia, do not seem to struggle in the department of food. Most reserves and national parks are well-stocked. Although seasonal variation in weight seem to be quite normal in northern and central parts of India, I never read a report about an otherwise healthy tiger starved to death in India. This is not true for Russia. Most tigers in India live in reserves, national parks and buffer zones. Although dozens of tigers are still poached every year (referring to my recent long post on tigers in Southeast Asia in the tiger thread), protection doesn't seem to be a major problem. The main problem of Indian tigers is a lack of room. That and proximity to humans. Outside of the reserves and the buffer zones, tigers often struggle to find a territory. Even moving from one district to another (referring to quite a few reports of dispersing young males killed while trying) can be quite dangerous. In many reserves, overpopulation is a real problem. Every year, dozens of tigers perish in territorial disputes in Indian parks and reserves. As confrontations tend to favour the largest individuals, they stand the best chance to reproduce in the long run. This no doubt has an effect on the size of male tigers in particular. I have no information on the length of captive Indian tigers, but what I found on weight suggest adult males in Indian zoos average 400-410 pounds (181,44-185,976 kg.). The heaviest I know of was 460 pounds. Wild adult male Indian tigers, however, could be quite close to the average of captive male Amur tigers. In some regions in northern and northeastern India, an average adult male in his prime could be well over that mark. Same for Nepal male tigers. 3 - CONCLUSIONS Although wild Amur tigers rapidly disappeared in the period 1900-1950, large individuals shot in that period were not uncommon. After 1970, however, wild Amur tigers declined in size. The decline could have been a cumulative result of two factors: the lack of genetic variation (as a result of hunting and the extermination of sub-populations) and limited opportunities to recover (referring to many decades of habitat destruction, prey depletion and poaching). Captive Amur tigers in European zoos are descendants of 119 wildcaught founders. Most founders were captured in the fifties and sixties of the previous century, when wild Amur tigers were a bit larger than today. The number of founders well exceeds that of other subspecies. The large gene pool could be the main reason their captive descendants are larger than their wild relatives today, but it has to be remembered that wild Amur tigers faced unfavourable conditions for a long time. Compared to Amur tigers, the gene pool of captive Indian tigers is significantly smaller. As there are different sub-populations in India, chances are not all of them are represented. This is important, as there were significant regional differences in size a century ago. Most tigers in India live in well-stocked reserves, national parks and buffer zones. This means wild tigers often have the opportunity to get to their potential. The limited amount of reserves, the small size of many and limited opportunities outside protected reserves often result in territorial disputes. As these tend to favour large individuals, chances are the present conditions will have an effect on the average size of males in particular. Apart from that, the larger gene pool no doubt has a positive effect on the amount of individual variation. IN Russia, on the other hand, individual variation seems to be quite limited. 4 - FINAL REMARKS 4a - Weight Based on what I have on captive and wild Amur and Indian tigers, I'd say the average difference between adult males not able to reach their potential and those able to is 50-100 pounds. Captive male Amur tigers, in contrast to their wild relatives, show a considerable range in size (360-650 pounds). In built, however, individual variation is quite limited. This was not true for the first generation. Not a few Amur tigers I saw in European zoos in the sixties and seventies of the last century, females included, were robust and large animals. They also had a different attitude (more aggressive). These tigers disappeared in the seventies. The captive Indian tigers I saw were a bit shorter and not as tall. In weight, most of them more or less compared to Indian tigers in Indian zoos (range 350-440 pounds). 4b - Length After reading v. Mazak's great book ('Der Tiger', third edition), I decided to measure the actual standing height of lions and tigers in zoos and facilities. The results compared to those Mazak found. Captive male Amur tigers average 96-106 cm. at the shoulder when standing. The average is just over 100 cm. Very large individuals can reach or even exceed 110 cm. I measured 3 adult male Amur tigers in a Dutch facility some time ago. These three averaged 287 cm. (9.5) in total length in a straight line. Measured 'over curves', they would have compared to an average wild male Amur tiger today (9.8). Those I consider in the know thought the three males I measured were a bit below par. According to them, an average captive male is about 9.7-9.8 in a straight line. Exceptional individuals can reach 10.6-10.8. I've never seen Indian tigers in European zoos, but I saw a few in circuses and rescue facilities. They were smaller than Amur tigers, but not by much. The main difference was in weight. Captive male Amur tigers were 80-100 pounds heavier than captive male Indian tigers. One of the most impressive 'Indian' tigers I saw was a circus tiger with very black stripes and a deep orange ground colour. They said he was a direct descendant of a wild tiger captured in the northern part of Myanmar (Burma). Although in very good shape, he had been removed from the show because of his character. He was about as long and tall as an average captive male Amur tiger, but more developed in the neck, shoulders and limbs because of his background. 4c - Character The male Amur tigers I saw seemed to live in a different dimension. Most of them were not interested in communication. Although they often appear to be calm and collected, male Amur tigers have been involved in a number of fatal incidents in European zoos and facilities. Same for females. The contrast with their wild relatives in this respect is striking. Wild Amur tigers only seldom attack humans. Man-eaters are few and far between. I've watched Amur tigers for many hours. Most adults are observative, patient and determined animals. They have an eye for detail, don't like to be disturbed and, as Vaillant said, can be quite vindictive. More than once, I saw a large male tiger kill a fly he had observed for some time. I also saw tigers attack humans out of nowhere. I later learned there was a reason in every case. When agitated or angry, male Amur tigers can rage for hours. Every big cat can be aggressive, but the only ones indulging in lengthy demonstrations were male Amur tigers. Although it seldom shows, violence seems to be more present in Amur tigers than in other tiger subspecies. Captive Amur tigers do not seem interested in other big cats. Circus tigers in particular seem to be more interested large herbivores. And bears. Brown bears, to be more specific. I'm not saying they're obsessed with bears, but it's quite close to that in many adults. Based on what I saw, read and heard, I'd say Vaillant was close to the mark regarding tigers and bears in Russia. This is one of the reasons professionals concluded his book was accurate in many respects. Captive Indian tigers, in contrast to captive Amur tigers, often show their emotions and intentions. Not seldom, they are described as intelligent. My guess is trainers and keepers mean Indian tigers are interested in interaction. I've seen quite a few responsive adult Indian tigresses. I noticed agitated tigresses comforted or addressed by a keeper often were able to distinguish between an impulsive reaction and a controlled response. This takes a lot of awareness and self-control. The contrast between captive and wild Indian tigers in this respect is remarkable. In spite of the limited number of wild tigers and the impressive number of reserves, tigers in India still kill dozens of humans every year. The main reason could be a lack of room. Many reserves are surrounded by villages. Not all tigers living in buffer zones are dangerous, but tigers wounded in a dispute and tigresses with cubs can be aggressive. If they would have more room at their disposal, chances are the number of incidents would be limited. Tourism also is a factor to consider. Wild tigers are solitary animals. When they meet humans, stress is the usual result. Although incidents in reserves have been few and far between, chances are some individuals could lose their innate respect. As incidents often have consequences for wild tigers, it's best to separate wild tigers and humans and limit tourism. |
| Users browsing this thread: |
| 1 Guest(s) |