Final answer:
Honeycreeper C, with its broad and sturdy beak, is adapted for breaking hard nuts and is thus a granivore. Honeycreeper D, having a long and slender beak, is specialized for feeding on nectar, hence is a nectarivore.
Step-by-step explanation:
The foraging habits of honeycreepers can be deduced from the morphology of their beaks. Based on the given information, we can infer that Honeycreeper C, which has a broad and sturdy beak, is adapted for breaking hard nuts. This kind of beak is characteristic of seed-eating birds, known as granivores, and is suited for crushing hard, tough seeds. On the other hand, Honeycreeper D, with a long and slender beak, is specialized for feeding on nectar. Such a beak is typical of nectarivores that need to reach into flowers to sip nectar. This aligns with the observation that the seed-eating bird has a thicker, stronger beak which is suited to break hard nuts, whereas the nectar-eating birds have long beaks to dip into flowers to extract nectar.