"These are the birds whose food is little."
Translation:Αυτά είναι τα πουλιά των οποίων το φαγητό είναι λίγο.
Yes, this isn't the smoothest sentence in the course but I think τροφή wasn't included yet.
This is an awkward sentence in English. I can't imagine using that to express:"these are the birds who have little food" ....or......."these are the birds whose food is sparse"
I agree (I actually went ahead and reported it as unnatural). In modern English at least, it gives the mental image of the birds eating food that is literally "little" (of small size). As you wrote, the more natural way to convey the idea that is intended is with "these are the birds who have little food" (even that is rather formal-sounding and without context can still convey that the food is small- even more common would be "these are the birds who don't have much food").
Indeed this is a sentence destined for removal or serious editing. "...who don't have much food or who have little food" might be the best but it strays far from the Greek. I'm going to include them.