Measurement and Data Collection in the Field
How much does that elephant weigh?
As part of our elephant research in Cameroon, we collect morphology data about the animals we find. Morphology is the term we use to describe the study of an animal’s physical body or its “structure”: its height and weight, the size of its feet or limbs, and so on.
Some morphological data is easy to gather. Some data, however, is very difficult to obtain. Perhaps the most difficult data to gather on an elephant is its weight. Obviously, we cannot carry a big scale with us into the rainforest, so we can’t just weigh the animal the way you would a dog or a cat. On the other hand, our experience has shown us that we can estimate an elephant’s weight by measuring three body features and then entering those numbers into a simple formula.
Here’s what we have to measure:
- the girth of the elephant at her heart; in other words, how big around is she?
- the length of the elephant;
- the circumference of one of her footpads (that is, how big around is the footpad?).
All of these measures are taken in centimeters. Next, we enter those numbers into the following formula:
(11.5 * heart girth) + (7.55 * length) + (12.5 * pad circumference) – 4016
The total we get from the formula above gives us a good approximation of the elephant’s weight in kilograms.
Click here to access a simple dataset of elephant measurements. This dataset includes age, heart girth, length, and pad circumference data for more than fifty elephants. Use this data, and the formula above, to estimate the weight of some or all of these animals. Once you’ve done that, ask yourself the following questions:
- do male or female elephants tend to weigh more; which tends to have a larger girth? which tends to be longer? which tends to have larger footpads?
- what is the relationship between age and weight? do elephants ever appear to “stop growing”? is it possible that older elephants get smaller as they age?
- what are the differences between the oldest and youngest males? what about between the largest and smallest females?