Parameters that influence blood oxygen carrying capacity (whole-blood
haemoglobin content, haematocrit and red blood cell count) were measured in
samples of 30 breeding, adult short-tailed shearwaters
(Puffinus tenuirostris) on Phillip Island, Victoria at
seven key stages of their reproductive cycle. The aim of the investigation was
to determine whether variation in blood oxygen carrying capacity during the
birds’ 7-month breeding cycle was correlated with variation in the
energy demands they experienced or was an incidental by-product of other
physiological changes. All the blood parameters varied significantly during
breeding, but the pattern of variation was only partly correlated with the
likely pattern of changing energy demand imposed on parents by their schedule
of breeding activities. The main trend conceivably related to energy demand
was that significantly higher values were recorded for these blood parameters
during the nestling stage than earlier in the breeding cycle. This could have
reflected the high costs of the very long foraging trips undertaken by parents
feeding nestlings, but it could also have occurred in preparation for the long
migration undertaken soon after breeding finished. It involved an ~10%
increase in blood oxygen carrying capacity above the lowest mean value
recorded during the breeding cycle and so other mechanisms must also be
employed to achieve the increase in aerobic metabolism likely to be required
at this stage. The lack of adjustment of blood oxygen carrying capacity to
energy demand early in the breeding cycle suggests that either oxygen delivery
was not a rate-limiting process for aerobic metabolism at that time or that
delivery was enhanced through other mechanisms. At egg laying, females had a
lower haematocrit and erythrocyte count than males, which could be
attributable to either estrogenic suppression of erythropoiesis or an increase
in osmotic pressure of the blood associated with yolk synthesis. Immature,
non-breeding birds attending the colony were of similar mass to adults, but
did not show the increase in the parameters determining blood oxygen carrying
capacity that occurred in adults later in the breeding cycle. Factors other
than changing energy requirements (dehydration, burrow hypoxia and
differential responsiveness to capture stress) that might have influenced the
pattern of variation in blood oxygen carrying capacity of adults during
breeding are discussed.
Microvascular experimental evidence on the relative significance of restoring oxygen carrying capacity vs. blood viscosity in shock resuscitation
