The claim that warm-blooded animals maintain constant internal temperatures through thermoregulation is a foundational biological definition of endothermy and homeothermy, so no citation is needed.
The claim states that warm-blooded animals maintain constant internal temperatures through thermoregulation. This is a matter of common biological definition and everyday scientific observation regarding homeotherms and endotherms. Therefore, per the instructions for step 0, this is common knowledge and no citations are required.