Background: In the tropics there is little variation in the length of day throughout the year, and it is always warm enough for a food supply, but altitudinal migration occurs in some tropical birds. There is evidence that this enables the migrants to obtain more of their preferred foods such as fruits.
Question: Where is it always warm enough for food supply?
Answer:<extra_id_0>.
<extra_id_0> In the tropics<extra_id_1>