as i dont know that what kind of radiation animals emit. as humans emit IR radiations so PIR sensors help to identify humans. pls suggest me if someone have knowledge about sensors which detects animals.
Warm blooded mammals and birds should be similar to humans as far as these sensors are concerned, amphibians and reptiles probably not.
Here are some thermal signatures from sensors that are more sophisticated, but in any case should give you an idea of the difference in body temperature from the ambient background temperature, of some parakeets vs a lizard.