Which one of these animals is not a homeotherm?

Chelone or marine turtles belong to the Cheloniidae family

This family is typically large marine turtles that are characterized by their common traits such as, having a flat streamlined wide body and rounded shell and almost paddle-like flippers for their forelimbs. They are a part of the class Reptilia. Eg. Green turtle.Reptilians are poikilothermic whose internal temperature varies considerably. It is the opposite of a homeotherm, an animal which maintains thermal homeostasis.

Both Aves and mammals are homeotherms.
Camelus - Arabian camel
Macropus - Eastern grey kangaroo
Both Camelus and Macropus belong to class Mammalia.
Pisttacula - Plum-headed parakeet, belongs to class Aves.