Mammals developed echolocation as an evolutionary response to night life or to life in dark, cloudy waters.
Long ago, bats that ate insects during the day might have been defeated in the struggle for survival by birds, which are better flyers and extremely sharp-sighted.
The most widely chosen pets are dogs, cats and birds of different types, while these are some of the usual choices, there are many of us who prefer having diverse kinds of pets.
With diverse choices come different prices too, we fully agree with you that a pet does not need to be treated as per its cost but still some animals are worth mentioning for their unusually high demand and price.
Frequency: For a sound wave, the number of waves that pass a given point in a particular amount of time.