ON THE EDGE OF EXTINCTION - A - THE TIGER (Panthera tigris)

[peter]

AMUR TIGER RESEARCH - THE CLAYTON S. MILLER THESIS - IV

I - RESULTS

1 - Average inter-kill interval and kills per year

" ... We evaluated the relationship between the inter-kill interval and weight of observed kills ... using all data from Pt100 and two sets of data from Pt99, one before the poaching attempt and one after a two-month recovery period. The average inter-kill interval between observed small prey kills (7,25 days) was shorter than the inter-kill interval between of between large prey kill sites (9,25 days), but the relationship was not strong ... " (pp. 19). 

" ... Monitored tigers made an average of 0,11 kills per day ..., or one kill every 9,1 days. Extrapolating our results to an annual rate for an individual tiger, these observed kill rates would result in an average of 40,1 kills per year. Our logistic regression model predicted slightly higher kill rates than observed in the field (one kill every 8,29 days or 44 kills per year) ... " (pp. 20). This corresponds to 7,5 kg. per day for an adult tiger.

A bit lower than previously reported results, that is. One reason was these were a result of extrapolation of what was observed in winter, when Amur tigers could be followed in the snow. Styudying Amur tigers in summer was impossible. Another reason could have been a declining prey base and smaller animals. The third reason could have been a change of diet in summer. Miller and the ones involved in his research thought Amur tigers could be preying on smaller animals in summer, thus increasing their kill rates in that season. The last reason could have been less large ungulates for the simple reason they are much less abundant than a decade ago, especially in unprotected areas (pp. 24).

Here's how the findings compared: 

*This image is copyright of its original author

*This image is copyright of its original author

 

2 - Energy requirements 

a - Goals and assumptions  

" ... The northern limit of tiger distribution is hypothesized to be constrained by densities of prey species. Given that Amur tigers exist at the lowest densities of ungulates for any known tiger subspecies, the challenge of understanding prey requirements and reproduction is particularly acute for this northern subspecies. As an impoverished prey base will support only occasional reproduction, determining the threshold consumption rate for reproduction is an important conservation question ... " (pp. 42).

" ... The conservation question for Amur tigers is then to manage ungulate harvest and poaching to achieve a necessary minimum prey density. Quantifying the energetic requirements of tigers allows scientists and managers to estimate nutritional carrying capacity ... " (pp. 43).

" ... The primary energetic activities of adult tigers are resting, traveling, eating, hunting and the periodic energetic costs associated with reproduction and thermoregulation. Time spent in different activities multipliede by the energetic costs of each activity results in an estimate of daily energy requirements. Reproductive female tigers experience higher energetic costs than males because of the additional costs of gestation, lactation and then securing sufficient prey biomass for 1-4 growing young ... "  (pp. 43).

" ... We have two broad goals, first to estimate tiger energetic requirements and then determine the consequences of these energetic requirements in terms of predicted prey requirements in single and multi-prey communities ... " (pp. 44).

Then formulas were constructed to describe and quantify every activity. Miller used a tiger's body weight to estimate the basal metabolic rate. It was assumed thermoregulation increased energetic costs by 15%. It was also assumed reproduction is the most energetically expensive activity. Furthermore, it was assumed that for tigers, like in cougars (for lack of better), meat and organs of prey species resulted in 1,890 kcal/kg. for all prey species (pp. 54). Finally, it was assumed that about 15% of each kill was lost.


b - Results

After a lot of computations, it was concluded an average tiger, in an average day, spends 7.5 hours at kill sites, 7.4 hours traveling, 9.1 hours resting and 1.44 minutes in hunting and attacking prey (pp. 56). Male Amur tigers spent 6.5 hours traveling per day and moved 7.6 km. a day in summer and 6.5 km. in winter. Adult non-reproducing Amur tigresses spent 7.9 hours traveling per day and averaged 6.6 km. per day in summer and 4.5 km. in winter (pp. 57-58).

For all sexes and seasons " ... energetic requirements were most sensitive to variation in tiger weights (41% of the variation), followed by time spent eating (22%), time spent traveling (18%) and time spent resting (11%). The last three parameters (travel speed, distance traveled per day and time spent hunting) only accounted for 8% of the total variation in total energetic requirements ... " (pp. 61-62).

In order to meet the energetic requirements, a male tiger needs to consume a minimum of 4.6 kg. of meat per day in summer and 5.3 kg. in winter (average 4.9 kg. per day year-round). For an adult non-reproducing tigress, the numbers are 3.4 kg. per day in summer and 3.8 kg. per day in winter (3.6 kg. per day year-round). From pregnancy to succesful dispersal, a tigress with an average litter needs to obtain an average of 7.3 kg. per day and a female successfully raising 4 cubs to dispersal needs to average 11.1 kg. per day (pp. 60).


c - The discrepancy between predicted minimum requirements and actual observations

" ... The consistent discrepancies between empirical observations and energetic modeling raise a series of questions. For example, are the models failing to accuratelu estimate energy demands or are carnivores killing more than they need to survive ... "? (pp. 63). Miller then offered some possible answers:

- carnivores strive to always have more food than might cause starvation;
- carnivores could face energetic costs researchers are unable to incorperate in their models, like injury, and
- carnivores traveling in deep snow could face increased energetic demands (pp. 64-65).


d - Conclusion

- Miller and those involved in his research concluded their model was accurate enough regarding conservational purposes to be used everywhere. It was also tested in the Sunderbans. 


3 - A few more tables

*This image is copyright of its original author

*This image is copyright of its original author

*This image is copyright of its original author

*This image is copyright of its original author

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