Which of these birds has the largest beak?

Toucans are members of the Neotropical near passerine bird family "Ramphastidae". They are brightly marked and have large, often-colorful beaks.

English naturalist Charles Darwin (1809-1882) thought the toucan's oversized beak was a sexual lure for attracting potential mates, while some modern-day biologists suggested it was either for peeling fruit or to warn off territorial rivals.

The beak of the toco toucan - the largest member of the toucan family - accounts for about one-third of the bird's body length, which is larger than the beak of any other bird for its size.

Although no one has been able to come up with a satisfactory explanation of how the toucan acquired its beak, a team of scientists has been able to show that whatever purposes it may have originally served, it now helps to keep the bird cool, just like the oversized ears of the African elephant.

A toucan's beak has a rich supply of blood vessels running along its surface so the bird's bill is suited to act as a means of radiating heat to keep the core temperature of the body stable.