Animal Life Spans
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How long do animals live? Man has been trying to answer this question for years, but until recently most of the life-span information resulted from keeping age records on captive animals. Although these records showed how long animals could live, the information was misleading.
Captive animals are protected from drought, flood, fire, and predators; they are fed regularly; and if injured or exposed to disease, they receive medical attention. This care helps them to live long, healthy lives. However, wild animals do not have these advantages. They live only as long as they are able to defend themselves and find food.
Determining the age of wild animals is very difficult, but research is producing some of the answers. Fisheries biologists have learned to read the growth rings formed in the scales, fin spines, ear bones (otoliths), and vertebrae of fish to determine age. During periods of rapid growth, the rings are far apart, but when growth is retarded, as in winter, the rings are close together. By counting the areas of concentrated rings, the biologist can tell how many winters have passed. This aging method is more accurate in the North, where seasonal temperatures are extreme, but it is not completely accurate since conditions other than winter are known to retard growth occasionally.
Some turtles also form yearly growth lines on their shells. In the case of the box turtle, these lines are considered reliable for the first five years and fairly accurate for the next ten. But after the turtle reaches fifteen years of age, the lines are no longer of any value in telling age.
Biologists can determine the age of some mammals by studying their teeth. The number and type of teeth indicate age in sheep and goats, but wear on the jaw teeth reveals a deer’s age. As the deer grows older, certain portions of its teeth are worn away from use. By examining the amount of wear, the age of the deer can be determined. This method is fairly accurate up to eight and a half years, but once the deer passes to this point, the teeth are worn too smooth to be of any help. As the teeth wear down, the deer is unable to feed properly. As a result, few deer live longer than ten years in the wild. Males of some species of wild sheep are believed to show age by growth segments in their horns; however, the segments remain the same after twelve or fourteen years, so older males cannot be properly aged.
The whale has a waxlike plug in its external ear. This earplug increases in length with age, and scientists believe a set of its alternating light and dark layers represents one year of growth. If this is true, whales have been credited with much longer life spans than they really have. Zoologists once believed whales lived 150-200 years, but the waxlike earplugs from hundreds of whales caught in the Antarctic fishing grounds show that none of the whales was more than 60 years old.
Trying to keep track of a wild bird to see how long it actually lives would be next to impossible; however, ornithologists have been able to age some wild birds from information received through banding efforts. A banded osprey was found dead on June 1, 1935. From the banding record, they discovered this one osprey, which had been banded as a nestling on June 19, 1914, was able to survive in the wild for almost 21 years. A European black-headed gull was captured twenty-four years and ten months after its banding, and a Caspian tern was collected twenty-six years after receiving its band. Records such as these give some idea of life-span potential, but few small birds grow old in the wild because predators and accidents usually cut their lives short.
Animal size does not necessarily indicate life span. The wild lion’s age compares with that of a domestic cat; larger breeds of dogs have shorter life spans than smaller ones; and a Shetland pony can outlive a regular horse. However, larger animals, as a rule, do live longer in the wild than smaller ones. One reason for this is that more dangers face the smaller creatures. Rising waters from a heavy rain can drown a small creature or destroy its home and food supply while only causing the larger animal to get wet or be uncomfortable. Predators also feed heavily on the smaller animals such as rabbits, mice, birds, and insects. So you can see there is a certain amount of safety that comes with size.
Smaller animals also may live at a faster body pace than larger ones. This means they may breathe faster, have a faster heartbeat, and eat more food in relation to body size to produce the energy required for this faster pace. As a result, the smaller animal’s body wears out faster, like a motor that constantly must be run at high speed.
The majority of insects live less than one year. Many cannot endure cold weather except during their egg stage, so they live their entire life cycle between spring and fall. Some insects, such as the mayfly, live as adults for only a few hours because they do not or cannot eat. Their whole existence is devoted to finding a mate and reproducing. The adult mayfly accomplishes this task in no more than eighteen hours. Although short-lived as adults, these insects may spend one to two years in the larval or nymphal stage before changing into adults. Cicadas, which live three to six weeks as adults, spend two to seventeen years as nymphs.
Activity of a creature also may determine its life span. The queen honeybee, who spends her time laying eggs for the hive, may live as many as five years. Worker bees, on the other hand, live no more than six to twelve weeks. During this time they are gathering pollen and producing honey. Both the workers and the queen in an ant colony have long lives for insects. Queen ants may live for fifteen to twenty years and the workers as many as ten years. However, the queen termite surpasses them all by living fifty years or more. Centipedes and scorpions live five to six years.
To give you an idea of how long some captive animals have lived, the following list has been prepared from information appearing in The World Book Encyclopedia, The Larouse Encyclopedia of Animal Life, The International Wildlife Encyclopedia, and various other publications. Not all captive animals live this long; these are the record makers. Our knowledge of animals in the wild will grow with time, but records from captive specimens may be all we will ever have for some creatures.
|Name of Animal||Life Span|
|Name of Bird||Life Span|
|Name of Reptile or Amphibian||Life Span|
|Name of Fish||Life Span|
1983 Animal Life Spans. Young Naturalist. The Louise Lindsey Merrick Texas Environment Series, No. 6, pp. 20-23. Texas A&M University Press, College Station.