Birds of the Same Feather Keep a Forest Together: How the Decline in Fruit-Eating Bird Population Harms Tropical Forests

A new study published in the Oikos journal has revealed the vital role fruit-eating birds play in dispersing the seeds of more than 90 percent of tropical trees. Size also matters since larger birds contribute more to plant regeneration than medium-sized birds.

Marcia Muñoz from Senckenberg Biodiversity and Climate Research Centre studied fruit removal and seedling recruitment in a tropical forest. Large-bodied bird species that weighed up to 1400 grams played a larger role in fruit removal than small-bodied species since they have higher energy demands and are able to eat a wider spectrum of fruit sizes than small birds. Because of their size, large birds were the only ones who could disperse certain large-seeded plants.

Muñoz saw the undeniable link between flora and fauna. "Especially large fruit-eating birds are declining due to habitat loss and hunting in the tropics. This is likely to cause a poor regeneration of some plant species. It may bring about profound change to the tropical forest as we know it."

Fruits with small seeds were more commonly consumed since they were more accessible to all birds in the forest. "This means if large birds become extinct in a tropical forest, not only the large-seeded plant species but also the small-seeded plant species lose important dispersers," explained Muñoz.

The researchers performed the study in two adjacent protected areas of tropical forest on the eastern side of the Colombian Andes. They recorded the consumption of around 17,000 fruits by birds and measured the most important characteristics of birds and plants, such as body size or seed mass. The researchers also counted the number of seedlings each plant species established at their study sites.

"Our results highlight that plants with large seeds are particularly successful in tropical forests and contribute an important part of their diversity. So if we are to conserve this diversity, we need to protect large fruit-eating animals that are crucial for the maintenance of these ecosystems," said Dr. Matthias Schleuning, a researcher at Senckenberg Biodiversity and Climate Research Centre and senior author of the study.