How to Estimate an Alligator's Length by Its Head Size

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The American alligator (Alligator mississippiensis) frequents bodies of freshwater from swamps, rivers and lakes to occasionally even swimming pools. These water loving reptiles are seen throughout their home range in the southeastern United States. When conducting population surveys, biologists estimate an alligator’s total length based on the length of a portion of its head. Since an alligator can cause serious harm to humans when approached, perform a visual measurement estimation of its head from a safe distance.

    Locate the the midpoint between the eyes on the skull of an alligator. At night, use a flashlight to locate the eyes. They reflect a reddish-orange or bright pink when light is shone on them.

    Estimate, in inches, the distance from the midpoint between the eyes to the midpoint between the nostrils. Record this number. If performing the measurement at night, use a flashlight to locate the nostrils.

    Convert the number of inches to feet with 1 inch equaling 1 foot. For example, if the distance from the midpoint between the eyes to the midpoint between the nostrils is 4 inches, the estimated length of the animal is 4 feet.

    To convert fractions of inches to feet, multiply the fraction by 12 inches. For example, if the distance from the midpoint between the eyes to the midpoint between the nostrils of the alligator is 5 ½ inches, convert the half inch to feet by multiplying 0.50 by 12 inches, resulting in 6 inches. The total length of the alligator is estimated to be 5 feet 6 inches. For one-quarter of an inch multiply 0.25 by 12 inches and for three-quarters of an inch multiply 0.75 by 12 inches.

    Check your answer. Male gators typically grow up to 18 feet in length, while females seldom exceed 10 feet. If your result is more than 18 feet, recheck your calculations or remeasure the distance from eyes to nostrils.

    Tips

    • Alligators tend to be less active when air temperature is below 70 degrees Fahrenheit. Visually estimating an alligators snout length may be easier during this time.

    Warnings

    • The American alligator is listed by the U.S. Fish and Wildlife Service as a threatened species, meaning it has protection from capture without a permit, whether on public or private land. Check with your state’s wildlife agency for protections laws in your area.

References

About the Author

Diana K. Williams is a certified Master Gardener, has more than a decade of experience as an environmental scientist, and holds a Bachelor of Science degree in biology and environmental studies from the Ohio Northern University. Williams is a winner of Writer’s Digest Magazine's annual writing competition.

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