The ratio of amount of haemoglobin to total surface area of erythrocytes in birds in relation to body mass, age of nestlings, and season of the year.

The research examined differences in haemoglobin concentration (g%), number of erythrocytes (mm-3), length and width of red blood cells (micron), and haematocrit value (%) in adult birds of 21 species with body mass ranging from 8 to 170 g, in eight species of altricial birds during the course of their development and in two species throughout the seasons of the year. Erythrocyte total surface area was taken to be the product of the surface area of a single red blood cell and the erythrocyte count, and the ratio of haemoglobin to the total surface area of erythrocytes was then determined. Erythrocyte total surface area scaled with haemoglobin concentration in all three of the above situations, with the result that the ratio of haemoglobin to total surface area of erythrocytes was constant at a mean of 0.53 +/- 0.11 pg micron-2. Changes in the total surface area of erythrocytes occur as a consequence of simultaneous changes in the size and number of erythrocytes, with haematocrit values remaining relatively constant. The constant value of the ratio of haemoglobin to total surface area of erythrocytes may be optimal for haemoglobin saturation with oxygen in the lungs of birds.