If some aviary species fly and others swim but, all are endothermic tetrapod vertebrates, then some aviary species fly and others swim but, all endothermic tetrapod vertebrates share what trait?

Answer choices:
- warm-blooded
 - Weight
 - fur and fat
 - sweating
 - Epidermis
 - feathers
 - retina
 - four limbs

 

      feathers    