Thursday, 22 December 2011

Energy Expenditure of Sasquatch

Sasquatch are big, therefore they require a large amount of food. This article attempts to calculate as closely as possible how food much would be required. Calculating the minimum amount will limit the error involved.  Calculating the minimum also makes it easier to discuss the plausibility of sasquatch's existence in terms of Ecology.

Quantifiable factors involved:
  1. Basal Metabolic Rate
  2. Movement Requirements for Foraging
  3. Thermic Effect of Food
Non-quantifiable factors:
  1. Thermoregulation
Basal Metabolic Rate
In order to calculate the amount of food required we must first look at Basal Metabolic Rate (BMR). BMR is defined as the amount of energy needed to sustain life at rest; calculated in thermoneutral environment and fasted state (maintaining body temperature and digesting food consumes energy) [1].
Dr. Wolf H. Fahrenbach calculated the BMR of Sasquatch in his 1998 paper using Kleiber's Law:
kcal/day = 67.6 x body weight^0.756
Initially I had considered using predictive BMR equations for use in humans. The rationale for this was that Kleiber's Law describes a general trend and is not ideal for estimating BMR in a single species of individual. Whereas the human predictive equations are specific (I assume sasquatch are metabolically similar enough to humans). However I discovered a few problems: (1) equations require unknown data such as age, sex, or body composition (% body fat). Estimating these would be an additional source of error. (2) These equations are linear and therefore applying them to sasquatch 2-6 times larger than humans is problematic since it contradicts Kleiber's Law. Also the equations only claim to be valid within normal human weight limits. (3) Plugging in the 100 Kg and 20% body fat in the Katch-McArdel and Cunningham equations gives similar results to the Kleiber equation.
In conclusion, the Kleiber equation is the best way to approach this issue.
Table 1: BMR relative to weight
Movement Requirements for Foraging
The American College of Sports Medicine (ACSM) Walking Equation estimates oxygen consumption (VO2) during walking in humans. VO2 is directly related to energy expenditure.
VO2 = resting component + horizontal component + vertical component
VO2 = 3.5  +  0.1(speed)  +  1.8 (speed) (fractional grade)
*speed in m/min, grade as decimal
We will omit the resting component because we have already calculated the BMR and will add the BMR in place of the resting component later on. The ACSM resting component is a rough estimate based on human averages. The equation gives VO2max in mL/Kg/min which can be converted to kcal/min by the co-efficient 1 L O2 = 4.9 kcal. Then multiply in the weight, speed and distance gives the total number of calories. Using this equation requires several assumptions about Sasquatch's physiology and behaviour:
Primary mode of locomotion - Assume Sasquatch moves around the forest primarily by bipedal walking.
Gait efficiency - Assume the efficiency of Sasquatch's gait is equal to humans. Given the mid-tarsal break theory gait would actually be less efficient than humans, Dr. Meldrum notes this in his paper. It is impossible to quantify how much less efficient so we will assume equal to humans. This is consistent with establishing a minimum energy requirement.
Speed - Assume average speed of walking is 5 Km/h. A conservative estimate based on what my GPS calculates as my average hiking speed while backpacking. The effect of speed is rather minimal.
Distance - Conservative estimate being the average distance covered per day is 20 Km/h. This equates to 4 hours of hiking at 5 Km/h. Personally I probably cover 10-15Km/day on average including work, chores, exercise. Obviously we have no data on the daily activities of Sasquatch but this estimation considers study of radio collar studies of Grizzly Bears. Fahrenbach notes, "Increased size also implies high mobility and a correspondingly large home range. A rare, individually identifiable Sasquatch was reported over a span of 8 years in several locales in Washington and Oregon, the most distant sites having a linear separation of more than 150 miles (240 km)." While the identification of the same individual is questionable, I agree that the range of sasquatch is likely very large, probably larger than Grizzly Bears. Finding food is one issue, the other is given the rare nature of the species they must have large ranges to find breeding partners.
Hills/terrain - An estimate of 5% grade (average) will be included in the equation. This accounts for the increased energy demand of walking up hill. 5% is a conservative estimate based on the mountainous terrain sasquatch is proposed to inhabit. This also includes the increased energy demand of walking on uneven ground.
The results:
Table 2: Energy requirements of walking 20 Km at 5% grade, 5 Km/h  for various weights (Kg).
The energy requirement just for walking around to find food increases dramatically as the size of the individual increases. Where increased size is a metabolic advantage for BMR it is a disadvantage for movement energy expenditure. This equilibrium is what prevents animals from evolving into larger and larger forms.

The Thermic Effect of Food
The Thermic Effect of Food, is the energy required to digest food. In humans this accounts for 10% of all energy expenditure and can be considerably more for animals that eat primarily plants. Sasquatch can be assumed to be omnivores and therefore probably have the same or similar 10% as humans. Although realistically in the wild access to simple sugars and refined carbohydrates is limited, this would suggest greater than 10% effect.

There is no way to calculate this other than to predict it would probably be more than humans. Aboriginal humans had fire, clothing, and shelter to keep warm while they rested. Without these the energy required for thermoregulation would be considerably more. However, this is impossible to quantify.

Sources of Error
There are many. Too many unknown factors: Activity, behaviour, diet, metabolic cost of thermoregulation, actual size, hibernation?, walking in snow, ...

Table 3: Estimated total energy expenditure relative to weight.
These are absolute minumum values. Is there enough energy available in the ecosystem to support creatures with caloric requirements such as this?
John Bindernagel Ph.D.- Dr. Bindernegel is a professional wildlife biologist who thinks it is plausible that sasquatch exist. Update: On a radio program Dr. Bindernegel was asked about this topic, he did not have a estimate in terms of calories. He dosen't consider calorie availability a limiting factor, he referenced moose living in the same ecosystems and having a similar body mass.
Bears do it - Bears have comparable body mass and probably similar caloric requirements.  Bears can consume up to 35 000 kcal/day. Food drives bear behaviour: "Bears are constantly in search of easily obtainable food sources", "The focus is feeding—along forest openings, trails, road edges and in campgrounds—sometimes around the clock." Bears have extremely sensitive sense of smell that allows them to find food efficiently, (ie. they can smell there is something to eat under a rock before they flip it over). This also means sasquatch probably compete with bears for food sources.
Aboriginal humans - Humans have existed in essentially every ecosystem in North America. Although caloric requirements would be considerably less. Humans have several advantages such as communication, team work, tool use, permanent shelter, fire, transportation (ie. canoes), community (live in villages) which have helped the species survive.

Energy expenditure does not preclude the existence of sasquatch since bears and humans have proven survival is possible in a wide variety of habitats. It does however make certain areas with greater abundance of food sources more likely to contain sasuqatch. For example, areas where aboriginals have been known to settle in large numbers, and/or areas where bears are abundant would have greater probability of finding a sasquatch.
Calculations such as these seem to suggest that it is less likely that 600 Kg and larger sasquatch exist.

Further questions:
  • If large amounts of food are important to sasquatch why has a starving individual never wandered into a town/farm/camp risking being seen to find a meal?
  • Why do sasquatch not associate food and people the way bears sometimes do?
  • What sort of special traits or adaptations do they have to allow them to find food?

Off-line References:
  1. American College of Sports Medicine. (2010) ACSM's resource manual for guidelines for exercise testing and prescription, 6th ed. Philadelphia: Wolters Kluwer.
  2. Meldrum, Jeff. (2006) Sasquatch: Legend meets science. New York: Forge

1 comment:

  1. "I began my adult life with the hypothesis that it would be possi­ble to become a Stone Age native. For over 30 years, I pro­grammed and conditioned myself to this end. In the last 10 of it, I would say I realistically experienced the physical, mental, and emotional reality of the Stone Age. But to borrow a Buddhist phrase, eventually came a setting face-to-face with pure reality. I learned that it is not possible for human beings as we know them to live off the land."

    -Gene Rosellini