Briefly describe a bird heart and circulatory system

The avian heart has evolved into a large and powerful organ with rapid muscular contractions. Generally the smaller the species the larger the relative heart size. Generally birds have hearts larger and ones that beat faster than mammals. The human heart weight amounts to .42 percent of body weight and the pulse rate at rest averages 72 beats per minute. The House Sparrow's heart constitutes 1.68 percent of the body weight and the pulse rate at rest averages 460 beats per minute. In the Ruby-throated Hummingbird these figures rise to 2.37 percent and a pulse rate of 615.