Ficus cucurbitina is an uncommon but widespread strangling fig found in tropical rainforests from South Thailand to the Philippines and Borneo.
F. cucurbitina figs are notable for two reasons (1) They are very large and (2) They are covered in very sharp spines which all point away from the base of the fig. Why would a fig that needs to be eaten so that the seeds are dispersed by animals be covered in spines ? The most likely explanation is that the prefered dispersers are hornbills and the sharp spines deter the figs from being eaten by Green Pigeons which predate the seeds.
Hornbills use their long bills to toss figs in the air and turning them round before swallowing them base first. This means that hornbills swallow Ficus cucurbitina figs with the spines pointing backwards , whilst Green Pigeons have short bills so that they have to swallow the fig straight from the twig i.e. with the spines pointing into their throat. In simple terms, Ficus cucurbitina has evolved to be a specialist hornbill dispersed fig.
The next time you are on a river watch how the egrets and herons swallow the fish they catch. These fish eating birds use their long bills to manipulate their prey so that they always swallow the fish head first to prevent the spines on the fish from sticking in their throat.
Photos by Zain Basriansya with thanks to Rahim Idris. Photos taken at Tibarau Panjang Village, Tanah Bumbu, South Kalimantan
All 5 species of Treron Green Pigeons in Borneo are fig seed predators. They use grit in their gizzards to grind up the small fig seeds as they pass through their digestive system.
There are 8 species of hornbill resident in Borneo. All 8 species are important fig seed dispersers. Hornbills swallow figs whole. The seeds are later defecated or regurgitated away from the parent fruiting fig tree.