Kissing Birds
These four-winged avians don't have feathers. Their wings are rigid membranes flexed by fluid pressure inside a capillary network. Otherwise their resemblance to birds is uncanny.
Instead of a beak they have a human-like mouth which they use by attaching to prey and generating suction to break the skin and blood vessels.

They range in size from dimunitive to medium, and do damage based on size.
Dimunitive= 1hp
Tiny= 1d3 hp
Small= 1d6 hp
Medium= 2d6 hp

The attack requires one round to attach and one to draw blood. Thereafter the creature will fly away. They may be gregarious if prey is plentiful.