Population density
Estimated density of elephants based on capture-recapture and distance sampling indicated population density increased in the study area. Baskaran and Desai (2000) had estimated a population density of 2.4 (± 0.11) for the year 1999–2000. Earlier studies by Daniel et al. (1987) indicated a much lower population density (a little over 1 elephant/km2) for the same area. But this earlier method used a coarse ratio method (known: unknown) to estimate the population size. However, Baskaran and Desai (2000) argued that despite the differences in methods used and the questionability of the precision involved the differences are significantly large to allow us to assume that there has been a major increase in the population size.
Despite poaching reducing the male numbers, the elephant population in the study area is increasing. Daniel et al. (1987) had pointed to this very fact in their study and stated that despite the high levels of poaching (male-biased) the population was growing, and this was a cause for worry given what then was a density of a little over 1 elephant/km2. Sivaganesan (1991) and Sivaganesan and Sathyanarayana (1995) had indicated that preferred tree species of elephants were declining rapidly and one of the main causes for the decline of adult trees was feeding by elephants. While this would have been an indicator for the local population other confounding factors like rainfall, fires (Suresh et al. 2010) and other herbivores (deer) suppressing regeneration were not studied and therefore the decline of these tree species could not be attributed entirely to elephants.
Density estimates by capture-recapture method
If these densities are extrapolated to the park it gives a population that is three times the size of the population estimated in 1987 (Daniel et al. 1987) using a similar method but covering the entire PA. There can be little doubt that the population has grown significantly in the last two decades, even if we assume that there was some underestimation in the past. What was apparent was that re-sighting (recaptures) was relatively poor in this study relative to that done in Nagarahole (Goswami et al. 2007). This would indicate that some sites are suitable for such studies while others are less so. The effort needed to get good sample sizes in less suitable areas would be high so this method cannot be recommended for all areas even if elephant densities are high. This is slightly higher than the density estimated using other methods but this could be because roads by and large are located in good terrain (also suitable for elephants) and close to water sources (attracts elephants) and some of the roads are especially designed for viewing wildlife (biased towards high-density areas).
Demography
Comparison of the age structure of the MTR with earlier data showed that the adult population has increased significantly due to an increase in adult females as shown by Desai and Baskaran (2000) (Table 1). The decline in the juvenile class could be due to either poor recruitment in the past several years or due to reduced breeding in the past few years. Desai and Baskaran (2000) had recorded only 9.5% calves in the population but cautioned that this could be due to natural reasons as more females are likely to calve in one year and fewer in the subsequent years. Similarly, the high proportion of calves (20.9%) seen during the present study could be an indicator of a normal cycle of high and low births based on the number of adult females that are available for breeding in any given year. However, the data indicates that we need to monitor systematically and regularly to detect any signs of a decline in breeding. The sub-adult class too has declined relative to the other two studies and it could also indicate lower recruitment and more animals moving into the adult age class. However, with a decreased juvenile age class and the sub-adult age class, there is a strong probability that breeding has been affected when the adult male: female sex ratio declined to 1:29 in 2000. It could also imply that the increased population is resulting in increased calf and juvenile mortality due to increased competition for resources and it is affecting recruitment. There is a clear need to monitor the population structure closely to ascertain changes and monitor trends so that we can better manage the population and address long-term conservation needs.
Sex ratio
Comparison of the sex ratios for different age classes in MTR showed improvement in male numbers relative to 1999–2000 period (Table 2). The adult male population shows marginal improvement, but the bulk of the adult class is made up of females whose population continues to grow rapidly in the absence of any major threat to this age class. This was also highlighted by Desai and Baskaran (2000). Change in the adult sex ratios of this scale (1:29 to 1:20) can come about by the addition of only a few males being recruited from the sub-adult class. This would be normal given the eight-year gap between the 2000 study and the 2008 (present) study. Given the fact that poaching in the region has not been reduced and there are also deaths of males due to HEC (retaliatory killings) and due to natural mortality, the adult male numbers have not changed significantly, clearly indicating a need for improved vigilance and increased anti-poaching efforts as also efforts to eliminate retaliatory killings. Park managers need to realize that mortality in the non-PA areas also affects their populations. Elephants have large home ranges which extend well outside the PA and into Reserve Forests (RF) areas that have fewer resources for protection and also have different management goals and priorities. This problem was highlighted by Desai (1991) and it needs to be addressed urgently through improved coordination between PAs and RFs and increased support to RF areas. There is a significant improvement in the sex ratio of the sub-adult age class but these changes can be expected to occur fast with improvement in protection as there would be rapid recruitment from the juvenile age class. The juvenile class too shows an improvement in the sex ratio and is comparable to the ratios in 1987.
Impact of poaching
Daniel et al. (1987) had reported that human was responsible for 80.7% of deaths in the present study area. Similarly, 88% of mortality was due to train collision and human-mediated in Rajaji National Park (Williams et al. 2007). However, in the present study, human-related mortality of elephants was 27.8% (Fig. 3). The major percent (61%) of mortality was due to natural causes like disease, injuries and predation by tiger (two calves). Sukumar (1985) estimated that human was responsible for 20% of female and 65% of male elephant death in South India so there has been a general decline in man-mediated mortality of elephants.
There were sex-based changes in mortalities that have occurred over time; while adult and sub-adult male mortalities were the highest (83%) in the earlier study period adult female mortalities were the highest (54.5%) during the present study. This shift is likely due to the reduced male numbers and consequently a reduction in poaching. Poaching has declined over time in terms of the number of males killed. The reason for this is twofold, first, there has been an increased anti-poaching effort that has made it more difficult to poach. And second, there has been a reduction in the number of adult males and also tusk sizes available today (in other age classes) do not make it lucrative to establish and run poaching networks. What poaching takes place is largely opportunistic and not organized as in the past where dedicated poaching gangs operated. However, males are still being killed at higher rates than they are present in the population. Considering this, it then becomes very important that efforts to contain elephant poaching and also retaliatory killings (HEC related) be minimized. Lower male mortality numbers should not create a sense of complacency that could allow organized poaching to return when male numbers are up.
Breeding
Daniel et al. (1987) suggested that disparate sex ratios even in the region of 1:5 would not affect breeding because males were polygamous and not all females come into oestrus in any given year. Given the approximately five years inter-calving interval then it would mean that an average of 20% of the female would breed in any given year. This would mean an effective male: female sex ratio of 1:1 even when the actual sex ratio is 1:5 in the population. Although the study by Daniel et al. (1987) did indicate that there are years with peaks and years with low births, likely, breeding would not get affected at even wider sex ratios. It is difficult to estimate at what ratio breeding would be affected but the present poor representation of sub-adults and juveniles (see Table 4.8) in the population may indicate that breeding has been affected. Adult male: female ratios of 1:29 estimated by Baskaran and Desai (2000) appear to have resulted in poor and the low proportion of calves (9.5%) in their study would indicate that but it could also be due to a naturally low birth year as mentioned by them.
Earlier in the 1980s, most matings were done by the large adult males which were over 30 years (Desai unpublished data) and were the only ones that had extended musth periods. But in the current study males below 20 years showed clear signs of musth (heavy temporal flows and swollen temporal glands) and sustained it for longer. In the 1980’s males in this age class only showed mild signs of musth with no temporal swelling and only a small fine small flow of temporal fluid and musth sustained for a week or so. This change shows that younger males that could never mate when the older males were alive were not taking on the role of breeding. Males as young as 10–15 years have been seen in musth. Such a shift in breeding might help overcome the problem of poaching of larger males but now the poaching has shifted to these smaller males and there are no males over 40 years of age in the population. This sustained decline of males would ultimately result in eliminating the genetic diversity of the male population as fewer and fewer males continue to breed.
There appears to be no significant change in the male-female association from the earlier study by Daniel et al. (1987). The decline in male numbers does not appear to have changed their behavioural pattern in terms of their association with females. No associations between males and female herds are seen in the 35 years and above age classes, as there are no males in these age classes in Mudumalai Tiger Reserve at present.
Makhna to tusker ratios
Among adult males, the ratio of Makhnas (tuskless males) to tuskers was 1: 4 which implies that makhnas make up 20% of the male population. Williams et al. (2007) estimated that makhnas constitutes 10% of adult males in Rajaji National Park. Whereas in Sri Lanka 90% of the sub-adult and adult bulls are makhnas (Katugaha et al. 1999). Daniel et al. (1987) had estimated that makhnas made up approximately 13% of the population during their study. In contrast to these habitats, Goswami et al. (2019) estimated a tusker to makhna ratio of 1.2:1 in Kaziranga National Park, suggesting that makhnas comprised ~ 45% of the male population. While the proportion of makhnas in the male population appears to have doubled almost but actual change is significantly greater as the tusker population was already severely depleted by poaching during the study by Daniel et al. (1987). This would mean that the original proportion of makhnas in the population would have been far less than the 13% estimated by them. While the continued decline in the tusker population would account for a significant part of the change in the proportion of makhnas it would not account for all the changes as we are now dealing with a new generation of males. When all the large adult tuskers were poached off in the 1980’s and early 1990’s, the adult makhnas were also eliminated in the 1990’s and in the early part of 2000’s due to HEC-related killing and one elephant was even captured due to HEC. Given their very small numbers of HEC related elimination and old age would have eliminated all the older animals. Thus we are dealing with a new generation of males and the increase in the proportion of makhnas would be due to an actual increase in their numbers rather than other factors alone. But when the bulk of the large tuskers were eliminated from the population by the 1990’s the large adult makhnas would have monopolized the mating and this could account for some of the increase in the population of makhnas.