How is being endothermic both and advantage and disadvantage for birds?

flying requires lots of energy, which demands a high metabolism. Enzymes need a certain temperature to work ideally, therefore, by maitaning a constant body temperature (endothermic), birds are able to ensure the ideal conditions for their enzymes which also ensures a high metabolism and high production of energy. If they were ectothermic, they would be unable to fly when its cold. Mst of the food they consume is used to maintain that constant body temperature. A disadvantage would be that birds have to consume alot more food compared to an other ecotothermic animal of the same size.