Why the bill is so large and brightly colored is still debated and may be complex. The bill has forward-facing serrations resembling teeth, which historically led naturalists to believe that toucans captured fish and were primarily carnivorous, but today we know that they eat mostly fruit. As there is no sexual dimorphism in coloration it is unlikely to be a sexual signal; It does aid in their feeding behavior (as they sit in one spot and reach for all fruit in range, thereby reducing energy expenditure).