Energetics and morphometrics of non-breeding albatrosses

The synchronous catastrophic mortality in the semelparous cuttlefish (Sepia apama), is an annual winter event in the coastal waters of southern Australia. This creates an abundant food resource that attracts large numbers of marine carnivores to the Wollongong coast, including several species of albatross. This provided the opportunity to investigate the nutritional requirements and energetics of non-breeding albatrosses at the nearby University of Wollongong research facilities. My objectives for these studies were: a) to determine the digestive (assimilation) efficiency of Diomedea albatrosses for cuttlefish; b) to measure the postprandial metabolism of albatrosses (2 species) with the aim of determining the energy cost of heating cold meals and the extent to which Specific Dynamic Action (SDA) contributed to food warming; and, c) to test whether the published values of 20% higher Basal Metabolic Rates (BMR) of large Diomedea albatrosses (6-10kg) compared to those for smaller species (Thalassarche, Phoebastria Spp.; 2.5-3.5kg) were maintained outside the breeding period. Reported values for albatross BMR suggested that mass-specific BMR (BMRm) of Diomedea was ~20% greater than for the Thalassarche genus. To confirm this observation, I measured BMR in four albatross species; wandering, Gibson’s, white-capped (Thalassarche steadi) and Campbell (T. impavida), using open system respirometry. BMR had not previously been measured for the latter three species, but the results of these measurements confirmed the existence of intergeneric difference in mass-specific BMR. From anatomical studies I found that D. gibsoni kidneys were some 20% larger than those of T. steadi. As kidney mass has been found to be a major contributor to BMR in other avian species, this result may partially account for the observed intergeneric BMR difference I used open system respirometry to measure albatross post-prandial metabolism (PPMR) for meal temperatures of 0, 20 and 40°C (body temperature  40°C) in Diomedea albatrosses (largest species) and the Indian yellow-nosed albatross (T. carteri) (smallest species). Combining these results with a mathematical model of albatross stomach thermodynamics, I was able to estimate components of PPMR and evaluate the fractional contribution of specific dynamic action (SDA) to the energy cost of heating cold meals. I estimated SDA to be 5.7% of gross energy ingested (GEI) and the cost of heating cold meals at 0°C to be >5% of GEI. Because of physiological delays inherent in thermoregulation following ingestion of cold meals, the resultant rise in metabolic heat production was over 50% above the calorimetric energy required to heat this meal. The contribution of SDA towards warming 0°C meals fed in amounts equivalent to 20% of body mass was estimated to be 17.9% and 13.2% in Diomedea and Thalassarche carteri, respectively. Consequently, the combined effect of these interacting processes results in an energy loss of more than 7% of GEI in meals consumed at these temperatures. One highly visible characteristic in which the petrel family differs from other avian species is their long narrow (high aspect ratio) wings. Many studies have demonstrated that petrels have a superior gliding/soaring ability, which they utilise to extract energy for transport from oceanic airflow (winds and air displaced by ocean swells). Low-cost transport is essential for survival of large albatrosses in pelagic ocean waters, because suitable forage is often distributed in patches separated by hundreds to thousands of kilometres. I expected that an investigation of petrel anatomy, particularly locomotor muscles, might reveal morphological features that related to lower transport costs. I was able to obtain 125 specimens of 18 species of Procellariiformes that were collected by the New Zealand Department of Conservation as by-kill recovered from commercial fisheries. I used these for extensive anatomical examination, particularly of locomotor muscles and central organs, as the size of these can be correlated with aspects of albatross energetics and ecology. From allometric relationships derived for petrel locomotor muscles I found that the locomotor mass for petrels scaled isometrically. As body size increased, however, petrels redistributed locomotor muscle mass; with pectoral muscle mass showing decreases while other flight and leg muscles increased. Overall, the locomotor muscle mass of petrels is 25.5% less than for other avian orders, and this is directly attributable to their smaller flight muscles. The pectoral muscles, which generate the power for flapping flight, scale with an exponent of 0.91, while wing loading scales with an exponent of 0.39. Field observations reveal that all petrels use a take-off run to become airborne and that this increases in length with increasing body size, thus demonstrating the physical effect of this divergent scaling. This has a limiting effect on flight performance in the larger species (albatrosses); take-off can be a difficult task in calm conditions or when flight performance is degraded by moulted flight feathers. Leg muscle power therefore provides an important power contribution during this critical stage of flight. Petrel leg and pectoral muscles are comparable in size, and the leg muscle scaling exponent of 1.16 demonstrates the capacity to offset the inverse proportionate relationship between pectoral and body muscle masses. The relatively small flight muscles of petrels results in reduced maintenance energy cost and a reduction in induced drag, and therefore lower transport costs during flight. These cost reductions imply a significant cumulative saving for species in which flight is a dominant feature of their life history.