Listening Script Vocabulary
(Section 4: You will hear a talk on the topic of desert animals. First, you will have some time to look at questions 31 to 40 [20 seconds]. Listen carefully and answer questions 31 to 40.)
L: Good morning everyone, and welcome to today's lecture. We're going to be continuing our investigation into desert animals by considering adaptations for survival in such an extreme climate.
Lack of water creates a survival problem for all desert organisms, animals and plants alike. But animals have an additional problem - they are more susceptible to extremes of temperature than are plants. Animals receive heat directly by radiation from the sun, and indirectly, by conduction from the substrate (rocks and soil) and convection from the air.
The biological processes of animal tissue can function only within a relatively narrow temperature range. When this range is exceeded, the animal dies. For four or five months of the year, the daily temperatures in the desert may actually exceed this range, called the range of thermoneutrality. Combined with the scarcity of life-sustaining water, survival for desert animals can become extremely difficult.
Fortunately, most desert animals have evolved both behavioural and physiological mechanisms to solve the heat and water problems the desert environment creates. Among the thousands of desert animal species, there are almost as many remarkable behavioural and structural adaptations developed for avoiding excess heat. Equally ingenious are the diverse mechanisms various animal species have developed to acquire, conserve, recycle, and actually manufacture water.
Behavioural techniques for avoiding excess heat are numerous among desert animals. Certain species of birds, such as the Phainopepla, a slim, glossy, black bird with a slender crest, breed during the relatively cool spring, then leave the desert for cooler areas at higher elevations or along the Pacific coast. The Costa's Hummingbird, a purple-crowned and purple-throated desert species, begins breeding in late winter, then leaves in late spring when temperatures become extreme. Many birds are active primarily at dawn and within a few hours of sunset, retiring to a cool, shady spot for the remainder of the day. Some birds, such as the Kingbird, continue activity throughout the day, but always perch in the shade.
A few desert animals, such as the Round-tailed Ground Squirrel, a diurnal mammal, enter a state of estivation when the days become too hot and the vegetation too dry. They sleep away the hottest part of the summer. They also hibernate in winter to avoid the cold season.
Some desert animals such as Desert Toads, remain dormant deep in the ground until the summer rains fill ponds. They then emerge, breed, lay eggs and replenish their body reserves of food and water for another long period.
Certain desert lizards are active during the hottest seasons, but move extremely rapidly over hot surfaces, stopping in cooler 'islands' of shade. Even their legs may be longer, so they absorb less surface heat while running.
Some animals remove heat absorbed from their surroundings by various mechanisms. Owls, for example, gape open-mouthed while rapidly fluttering their throat region to evaporate water from their mouth cavities. Many desert mammals have evolved long legs to release body heat into their environment. The enormous ears of jackrabbits, with their many blood vessels, release heat when the animal is resting in a cool, shady location. Their relatives in cooler regions have much shorter ears.
These are just a few examples of the ingenious variety of adaptations animals use to survive in the desert, overcoming the extremes of heat and the lack of water.
Eg. Squirrels sleep in parts of summer and winter means they sleep in parts of winter, which is incorrect. Therefore, summer is the only correct answer.