In a new study to prove that a group of antioxidants called flavonoids boost the immune system, ecologists have shown that fruit-eating birds select fruit with the highest concentrations of antioxidants that help them maintain their health.
Researchers from the University of Freiburg and the Max Plank Institute for Ornithology in Germany offered a group of blackcaps a choice of two foods during a study, reported online in the British Ecological Society's Functional Ecology.
The foods were identical in all respects except for the amount of flavonoids they contained.
The researchers observed that the blackcaps actively selected the food with added flavonoids.
Upon testing whether or not the flavonoids had an impact on the birds' health, the researchers found that, compared with birds not fed the antioxidants, blackcaps that ate modest amounts of flavonoids for four weeks had stronger immune systems.
"We fed the birds an amount of flavonoids that they would obtain by eating 1-2 blackberries, bilberries or elderberries a day. We used this modest intake of flavonoids because high quantities are only available during the limited time of maximum berry abundance," said the lead author of the study, Carlo Catoni of the University of Freiburg.
"Our study shows for the first time that flavonoids are beneficial compounds that can boost the immune system in a living organism. We also found that wild birds actively select food containing flavonoids. Our results have important implications for the study of ecology and immunity in birds, and for the evolution of the relationship between plants and the birds and animals they rely on to disperse their seeds," Catoni added.
The researchers believe that the birds were able to tell which food had added flavonoids because flavonoids made the food a darker colour.
They, however, concede that the blackcaps know that the darker berries contain more flavonoids, and which is why they prefer them.
"Studies by other ecologists and our own group have shown that blackcaps do not show a colour preference if food is nutritionally identical, so we are confident that our results are due to a learned selection for flavonoid content and not due to innate selection of darker food per se," Catoni says.
The researchers claim that their study is the first to show that flavonoids have boost the immune system in a living being, as opposed to test-tube studies.