Nutrition and the condition of elephant populations

In ultimate terms, a particular diet is expressed through body condition, health, and reproductive vigor in the evolutionary fitness of an individual. It has been well documented in African savannas that adverse changes in habitat conditions, such as during a drought, result in loss of body condition among elephants and demographic changes through higher mortality and lower reproduction at the population level. Under normal conditions, systematic differences in diet among herds or clans could also be reflected in their physiological and demographic status. These relationships are not straightforward, and empirical data for elephant populations are scanty.

One of the early studies by Peter Albl on physical condition among elephants culled in the Luangwa Valley, Zambia, found that the kidney-fat index (weight of kidney fat/weight of kidney), a proxy of physiological condition, declined sharply in all age and sex classes by the end of the dry season (table 5.4). He suggested that an index of 10% was the threshold between good and poor condition. Morphological criteria such as buccal, temporal, and scapular depressions were generally related to age. The lumbar depression, however, correlated with the kidney-fat index and could be used for evaluating body condition.

When Richard Laws and Ian Parker examined various ecological traits in the elephants culled at Murchison (Kabalega) Falls National Park in Uganda during the 1960s, they found several differences between the populations to the north and the south of the Nile River. The South Bank population existed at a higher density in habitat that was in a more advanced state of transformation into grassland. The more nutritionally stressed elephants here also had a lower rate of reproduction, as calculated from the intercalving interval. To compare metabolic and nutritional status of the two populations, a series of biochemical investigations was undertaken. The amount of hydroxyproline, an amino acid derived from the breakdown of collagen, excreted in urine was

Table 5.4

Seasonal comparisons of certain indices of physiological condition in African elephant populations.

Population

Hydroxy-proline : Season of Creatinine Sampling Ratio

Source

Luangwa (Zambia)

Wankie (Hwange)

(Zimbabwe) Kabalega North (Uganda)

Kabalega South (Uganda)

Rwenzori (Uganda)

Wet Dry Dry

Dry Wet

Dry Wet Dry

52.1

26.4

47.6

34.5

20.0

36.3

58.5

69.7

61.8

64.3

Albl (1971)

Williamson

(1975) Malpas (1978)

Malpas (1978) Malpas (1978)

examined by K. G. McCullagh in various age classes from both populations. The results, usually expressed as the ratio of hydroxyproline to creatinine, provide an index of the rate of growth. Surprisingly, the results indicated that the South Bank elephants had a higher growth rate than the North Bank ones. It turned out that the South Bank population had been sampled during the wet season, while the North Bank samples had been collected during the dry period. The seasonal differences in nutrition and growth obscured any interpopulation differences that may have existed. When Laws's team examined another proxy of physiological condition, the kidney-fat index, no significant differences were again seen between the two populations.

To rectify this anomaly in sampling, Robert Malpas undertook even more detailed investigations of diet and condition of elephants at the same sites about a decade later. Another surprising result awaited him. The kidney-fat index of elephants, both to the north and the south of the Nile, was higher during the dry season than in the wet season. Forage consumed during the wet season actually had higher protein levels, as seen from stomach content analysis. Blood urea levels also reflected this higher protein intake during the wet season. Why then did the kidney-fat index show this unexpected reversal? One explanation is that in seasonal habitats it is better for elephants to mobilize protein and other energy resources for growth during the wet season and not for fat storage. As the quality of forage declines with the approach of the dry season, it is adaptive to change strategies and to build up fat reserves to tide over a difficult period. Bone marrow fat was also slightly higher during the dry months in Malpas's samples. B. R. Williamson's investigations on elephants culled in 1971 at the Wankie (Hwange) Park in Zimbabwe showed even higher kidney-fat indices during the dry season. He concluded that the Wankie elephants, which incidentally were mainly browsers, were in good condition.

Comparable data on Asian elephants are not available. From visual criteria, such as those described by Peter Albl, I observed that an elephant clan in the Biligirirangans, which mainly browsed in bush habitat during the dry season, seemed in much better condition compared to another that grazed more in deciduous forest (fig. 5.8).

A possible alternative to the kidney-fat content and hydroxyproline excretion is intestinal parasite loads. T.N.C. Vidya and I examined intestinal parasite egg densities in elephant dung, but did not find any clear relationship between body condition and parasite loads. Dry season parasite loads, however, were higher than wet season loads. This line of investigation has to be pursued in more detail.

Figure 5.8

An adult female Asian elephant in poor body condition at the end of the dry season in Mudumalai Wildlife Sanctuary, India. This elephant died less than 2 weeks after this picture was taken.

Figure 5.8

An adult female Asian elephant in poor body condition at the end of the dry season in Mudumalai Wildlife Sanctuary, India. This elephant died less than 2 weeks after this picture was taken.

The links between body "condition" and fitness in demographic terms are not clear from the empirical data. Perhaps too much should not be read into assessments of condition in elephants.

It is known that elephants lose fat stored under the skin during the dry period. There could be redeployment of fat reserves between the seasons. The loss of subcutaneous fat and body weight during the dry, hot season could also aid in efficient thermoregulation. Excessive protein intake is also undesirable during the dry season because nitrogen excretion requires more water, which may be scarce. It can be expected that animals are physiologically adapted to a recurring dry season. Only extreme conditions, such as a severe drought, could threaten their survival and test the resilience of a population. Ideally, a measure of vigor and resilience, incorporating demographic and physiological traits, should capture the condition of a population. For the elephant, however, such a measure still eludes us.

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