Mammals and birds tend to eat much more, relatively, than other vertabrates. Why?

Answer 1

They are warm blooded animals, therefore they have to spend energy to maintain their body temperature by eating more.
The main advantage is that they are more active as they are less dependent on their surroundings.
Insects, reptiles, amphibians, fishes are cold blooded animals which body temperature fluctuates with their surrounding and they don't need to spend energy keeping their body heat, thus less food is needed.

Answer 2

Birds need an incredible amount of energy to fly. That is their excuse. If the other vertebrates are cold blooded they would need less food energy than mammals because they are relying on sunshine and warm burrows to keep their-selves at a temperature where they can be active instead of using food energy like mammals do.

Answer 3

im making an intelligent guess here. its because mammals and birds are both warm blooded and need more energy so they consume more food.