This 20 October 2018 video says about itself:
When resources run short, the sharp-beaked finches of Wolf Island turn into vampires to survive. Dr Alex Bond, Senior Curator of Birds at the Museum, explains the unexpected behaviour of these small birds. Blood Thirsty was captured by Thomas P Peschak, and won Wildlife Photographer of the Year 2018 in the Behaviour: Birds category. Discover more about this image here.
Why Evolution [of birds] Goes Wild on Islands: The Science of Adaptive Radiation: here.