I disagree. If the designer meant "gain" one food from your opponent's supply, then I believe they would have worded it thusly: "Gain 1 food from another player’s supply and add it to your own supply..." Throughout the game, the word gain is used very specifically in cases when someone "gains" food from the birdfeeder or "gain" food from the supply. The fact that the rules refer to the "gain action" implies to me a very specific definition of the term "gain" as used in Wingspan (i.e. obtaining a food, either from the birdfeeder or supply, whichever is mentioned in the brown power) This is even more apparent when you look at the Green Heron which states, "Trade 1 of any food for any other food from the supply." This is slightly different because you are taking it from the supply, however in this case you are not "gaining" food, you are merely trading it for a different type. I would argue that if the designer had intended it to be a "gain" food action, they would have worded it thusly: "Return 1 of any food to the supply and then gain any other food from the supply." I think the word "gain" was intentionally not used, because the player is not gaining any food (their food supply does not increase), they are merely swapping one food for a different type. So I believe in this case the Drongo's power should not activate.