The following description has been taken, with permission, from Softbills.org-
The term softbill is not a scientific one and has been used, and more often misused, in aviculture for numerous years. It is a very misleading title, as many species that fall into the category do not have a soft bill at all; anyone who has ever been attacked by a hornbill can attest to this.
The proper use of the term is in reference to the ‘soft food’ diets which basically fall into the following six categories:
This sixth diet type is usually in association with one of the above, as very few birds are solely foliverous, a few species of Galliforme come to mind, however they are not considered to be Softbills.
A more recent definition by Clive Roots is, “Cage and aviary birds with relatively soft bills, which feed upon insects* and soft plant material and whose young are helpless at birth”.
- including other larger animal prey
This latter definition does discriminate against a few species, however as can be seen, the definition is very subjective and can encompass numerous species not generally included in the group.