Counting rhinos is hard work! Think of what would happen if you went into the woods and tried to count all of the birds around you. Some birds would be flying all over the place, and some would hide as soon as they saw you. Other birds would be up in trees and you would never even know they were there. So, if you went into the rainforest and tried to count all the Javan rhinos, you would most likely count zero!
Obviously, rhinos cannot fly, but you get the picture—rhinos can be very secretive and do not like to be around humans. What is more, the rainforest is thick with thousands of trees and plants bunched together. So, we needed to come up with creative ways to use science to count the rhinos, similar to the way a detective uses clues and logic to solve a mystery!
In the past, scientist-detectives have used clues like rhino footprints (and even rhino poop!) to estimate how many Javan rhinos live in the park. But those things cannot give a very accurate estimate.

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Go to source: https://kids.frontiersin.org/article/10.3389/frym.2019.00121