Birds need so much food energy to maintain their body temperatures tha

Birds need so much food energy to maintain their body temperatures that some of them spend most of their time eating.
But a comparison of Mifune, a bird of a seed-eating species, to Rossi, a bird of a nectar-eating species that has the same overall energy requirement, would surely show that Mifune spends more time eating than does Rossi, since a given amount of nectar provides more energy than does the same amount of seeds.

Assumptions: Its takes more time to consume a seed than to consume same quantity of nectar.

The argument relies on which one of the following questionable assumptions?

(A) Birds of different species generally do not have the same overall energy requirements as each other.
This is general case whereas we have specific case where do have same requirement.

(B) The nectar-eating bird does not sometimes also eat seeds.
sometimes cannot be generalized for all circumstances.
This cannot be assumed.

(C) The time it takes for the nectar-eating bird to eat a given amount of nectar is not longer than the time it takes the seed-eating bird to eat the same amount of seeds.
(This is inline with our assumption above.)

(D) The seed-eating bird does not have a lower body temperature than does the nectar-eating bird.
(Not sure about this.)

(E) The overall energy requirements of a given bird do not depend on factors such as the size of the bird, its nest-building habits, and the climate of the region in which it lives.
(We don't need to assume this sentence as its negation does not affect the conclusion. The overall energy dependency on any factor does not affect its eating method, duration and quantity.)