Why did animals need to eat/be fed for a year in the Ark?
"Oh, because they need to eat", you'd say, but really the Mabul was one big miracle, overriding all laws of nature - physics, geology, zoology, biology, genetics and whatnot.
Why in this huge miracle did animals need to eat? This problem was easily "circumvented" for the Israelites in the desert with Mannah. This "natural behavior" actually caused more additional miracles to be performed - miraculous preparing of the food for all animals, miraculous feeding, taking care of poop etc.
Why couldn't G-d simply stop them from eating for a year?