Darwin's finch foraging behaviour and naris size

The avian beak is a key morphological trait used for foraging. If
parasites alter beak shape, we expect changes in host foraging behaviour.
Nestling Darwin’s finches on the Galápagos Islands experience naris size
enlargement caused by Philornis downsi larvae. We predict (1) altered
foraging behaviour in birds with malformed beaks from P. downsi. To test
the evolutionary implications of naris malformation, we predict (2)
changes in foraging niche overlap between sympatric species, and (3) worse
body condition in birds with malformed beaks. Our focal species are small
tree finch (Camarhynchus parvulus), medium tree finch (C. pauper), hybrid
tree finch (Camarhynchus spp.), and small ground finch (Geospiza
fuliginosa) on Floreana Island. With the exception of hybrid finches,
Darwin’s finch species with malformed beaks exhibited increased surface
prey removal and decreased hidden prey extraction during foraging. Naris
size enlargement, and different beak size traits per species, was
associated with worse body condition in Camarhynchus finches. Divergence
can be rapidly undone when introduced parasites alter functional
morphological traits that create ecological distinctiveness in species.