When parasites damage birds' beaks, the whole environment can change

Parasitism is the most common feeding mode on earth. But how do parasites affect the feeding behavior of their hosts? Darwin’s finches of the Galápagos Islands have a parasite called the avian vampire fly, which lay its eggs inside bird nests. When the eggs hatch, the immature flies enter the nestlings’ beaks via their nostrils and feed on their blood and tissue. The few nestlings that survive tend to have deformed beaks. We wanted to find out how this beak damage changes a finch’s body condition and feeding behavior once it leaves the nest. This study was conducted in the Galápagos Islands over 10 years. We monitored four species of Darwin’s finches and measured their body conditions. Overall, adults with damaged beaks were in poorer condition and changed their feeding behavior. This study shows that parasites can have long-term effects on the feeding behavior of their hosts.