Hawaiian honeycreepers (birds), consisting of 50 species, some of which are now extinct, represent a much more diverse lineage than Hawaiian thrushes. Honeycreepers have a remarkable variation in bill morphology, whereas Hawaiian thrushes exhibit far less morphological variation. Bill morphology is strongly linked to the resources available for these birds to eat. This suggests that in honeycreepers may have occurred as a result of

the oxygenated blood then leaves the lungs through pulmonary veins, which return it to the left heart, completing the pulmonary cycle. this blood then enters the left atrium, which pumps it through the mitral valve into the left ventricle. from the left ventricle, the blood passes through the aortic valve to the aorta.

deoxygenated blood leaves through the right ventricle through the pulmonary artery. from the right atrium, the blood is pumped through the tricuspid valve (or right atrioventricular valve), into the right ventricle.