Animals deploy a range of strategies to increase their chances of survival through difficult environmental conditions.

One particularly clever strategy is hibernation. A black bear, for instance, will drastically increase its food intake when it senses winter approaching. This phase of enhanced caloric intake, called hyperphagia, allows the bear to build up its fat reserves for the long winter ahead. It will also prepare a den-usually located in sheltered spots such as caves, hollow trees or burrows-where it can hibernate uninterrupted. As the bear enters hibernation, its metabolic rate drops, and it undergoes physiological changes such as reduced heart rate and breathing rate. This helps minimize energy expenditure. The bear will remain in hibernation until spring when food and weather conditions become more favorable.

What's less common-but equally clever-is "estivation." Estivating animals pursue the same survival strategy as the black bear, but they do it during the summer months when environmental conditions pose a different set of challenges-such as when the temperature gets too hot or when food or water become scarce. Here are three animals that use estivation to increase their already impressive lifespans.

The West African lungfish is noteworthy for many reasons, not least of which is its ability to estivate for long periods of time-in some cases, up to a year. It is a freshwater fish. Because many of the rivers and streams it inhabits shrink or dry up during the dry summer months, it has evolved the ability to burrow itself into the mud and enter a state of hibernation/dormancy, not emerging until more favorable weather conditions occur. Amazingly, the West African lungfish can survive for years without any food at all.

Aside from its ability to estivate, the lungfish is unique in that it is only one of a few fish species that possesses both lungs and gills, allowing it to breathe above and below water. This ancient adaptation is thought to be the precursor for animals making the transition from water to land, something that occurred approximately 370 million years ago.

During estivation, the lungfish will burrow a foot or so into the mud at the bottom of drying ponds or rivers, where it secretes a mucous cocoon that hardens to form a protective barrier. This cocoon helps retain moisture and insulates the fish from extreme temperature fluctuations. During estivation, the lungfish undergoes a significant reduction in metabolic rate, entering a state of torpor that allows it to survive on stored fat while relying on its lungs to breathe air through a mucus tube, as oxygen levels in the encased environment become insufficient.

Using strategies such as estivation, lungfish can survive in the wild for up to 25 years or longer.

The desert tortoise, native to the arid regions of the southwestern United States and northwestern Mexico, has evolved several adaptations to survive the harsh desert environment, including a sturdy, domed shell that offers protection from predators and the elements. Its diet primarily consists of drought-resistant plants, such as grasses, cacti, and shrubs, which provide it with the necessary nutrients and hydration. The tortoise's ability to store water in its body tissues is crucial for enduring the long periods between infrequent rainfalls.

To cope with extreme heat and prolonged dry conditions, the desert tortoise, like the lungfish, undergoes a period of estivation. As temperatures rise and water sources diminish, the tortoise digs and retreats to a burrow. Inside the burrow, the tortoise reduces its metabolic rate significantly, entering a state of dormancy that allows it to conserve energy and moisture. During estivation, the tortoise remains inactive and relies on fat reserves accumulated during the wetter, more active months. This period of dormancy can last several months, typically from late spring to early fall, until cooler temperatures and the availability of moisture prompt the tortoise to emerge and resume foraging and other activities.

Using strategies such as estivation, desert tortoises can live for 80 years and, in some cases, even longer.

The Gila monster is a large, venomous lizard native to the southwestern United States and northwestern Mexico. Characterized by its robust body, bead-like scales, and strikingly vibrant coloration with orange and black patterns, the Gila monster is one of the few dangerously venomous lizards in the world. It is well-adapted to its desert habitat, where it primarily preys on small mammals, birds, and eggs. Its venom, delivered through grooved teeth, serves both as a defense mechanism and as a means to subdue prey.

To survive the harsh, hot conditions of its desert environment, the Gila monster also undergoes periods of estivation during the peak of summer. As temperatures soar and food and water becomes scarce, the Gila monster retreats into a burrow or a rock crevice to escape the extreme heat. During estivation, it reduces its metabolic rate, which helps conserve energy and moisture. The lizard remains largely inactive, relying on fat reserves stored in its tail to sustain it through these hot and dry months. Although they may occasionally venture our a night during this period of extreme weather, the Gila monster emerges regularly when the weather cools or the monsoonal rains begin and food sources become more abundant.

Using strategies such as estivation, Gila monsters can live for 30 years in the wild.