Almost every species of land bird in the Galapagos Islands has expanded its diet to include nectar and pollen from flowers, finds a new study in Nature Communications. Such a large expansion of a feeding niche has not been reported previously among vertebrates and suggests that birds act as key pollinators across the archipelago.
Isolated oceanic islands like the Galapagos typically harbour a much lower diversity of plant and insect species than mainland areas, since dispersal over large expanses of water is often unsuccessful. In contrast, bird species may be able to reach these areas but face a limited range of insect and plant food when they arrive. As a result, species may broaden their diets to include floral resources, although the extent to which this occurs across island archipelagos is not known.
Anna Traveset and colleagues measure flower visits and pollen transport by Galapagos land birds and find that every species they observed interacted directly with flowering plants. This represents the 19 most abundant land birds out of the total 23 species found in the islands, who together interact with more than 100 different species of plants. Comparing the network characteristics of bird-flower interactions with those from other mainland and island ecosystems, they find that the Galapagos network is more highly connected, indicating a greater degree of diet generalisation.
This generalisation means that birds do not discriminate between interacting with native or invasive plant species, suggesting that although feeding niche expansion may have aided the birds’ initial survival on these islands, it may also be playing an unwanted role in the pollination of invasive plants.