Some animals are particularly sensitive to changes in their habitat, so a decrease in numbers can alert scientists that something might be wrong.
Science: Biological sciences
Some animal species, such as frogs, are particularly sensitive to changes in their habitat, such as pollution. Changes in the health or numbers of these species alert scientists to the possibility of a problem with their habitat.
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Bring Back the Frogs
Lesson Plan - Nature's Red Flags / Bring Back the Frogs