BRANTA — Philip F. Battley
Behavioural ecophysiology of migrating Great Knots
Institution: Griffith University, Brisbane, Australia
Supervisors: T Piersma, K Hulsman
Details: PhD 2002 (Completed)
Address: Department of Mathematics and Statistics, University of Otago, PO Box 56, Dunedin, New Zealand (Oct 2005) Email
Subject Keywords: migration, shorebird, wader, ecophysiology, energetics, moult, flight, body composition, metabolism, migration timing
Species Keywords: Great Knot Calidris tenuirostris
I studied the behaviour and ecophysiology of the Great Knot Calidris tenuirostris, a medium-sized migratory sandpiper, in Roebuck Bay, northwest Australia, and Chongming Island, Yangtze River mouth, eastern China. Great Knots breed on mountaintops in eastern Siberia and most spend the non-breeding season in northern Australia. They migrate north in late March and April, flying more than 5,400 km direct to eastern China and Korea, before refuelling in the northern Yellow Sea and departing for the breeding grounds in late May.
A comparison of body composition of birds caught before migration from northwest Australia and birds caught after migration in China found that, in addition to the expected use of fat deposits during migration, lean tissue of most internal organs was reduced after flight. The largest reductions were in the flight muscles, skin and carcass remains. Significant decreases were also found in the salt glands, intestine, liver and kidneys. This is the first demonstration of extensive lean tissue catabolism in migrating birds, and shows that the 'airplane refuelling paradigm' of Odum et al. (1964), which claimed that only fat content varies in migrating birds, does not hold. The reduction in lean mass was reflected in a 42% decrease in basal metabolic rate (BMR) after migration. Variation in BMR was associated with variation in the flight muscle mass and intestine mass. Captive premigratory Great Knots that underwent an enforced fast showed a similar reduction in BMR. The relationships between BMR and body mass in between- and within-individual comparisons differed from the relationship typically found among species. The slopes (exponents) of log-log regressions of BMR against body mass were among the highest known in birds (intraspecific comparison, slope = 1.36; intraindividual comparisons, mean slope = 2.23). Predicting BMR from interspecific allometric equations in not possible during fuelling and migration periods.
Body composition changes indicated that migrating Great Knots conserved protein as efficiently as any bird, active or inactive, drawing as little as 4% of their energy from protein. Nevertheless, the magnitude of the flight from Australia to China resulted in substantial lean tissue catabolism. Comparison of the body composition of wild migrated knots with fasted birds indicated that both groups had broken down lean tissue from most organs in the body with the exception of the brain, though nutritional organs were substantially more reduced in the fasted birds.
Such lean tissue breakdown means that there is no 'fixed' tissue mass component in long-distance migrating birds. A recent predictive model of bird flight by Colin Pennycuick (1998) was modified to allow lean tissue breakdown from the 'airframe' as well as the flight muscles (airframe being the total mass minus fat mass and flight muscle mass). The model was also modified to allow protein breakdown in the flight muscles from only myofibrils. Predicted flight lengths for an average Great Knots caught in Australia before migration were sufficient to reach China, but only if the body drag coefficient used was much lower than the previous default values (0.10 to 0.17 c.f. 0.25 to 0.40). The model did not accurately predict the flight muscle mass on arrival, always removing too much tissue during flight.
Behavioural heat avoidance was studied during fuelling in Roebuck Bay. Birds with higher breeding plumage scores (i.e. better fuelled) had a higher incidence of heat avoidance (primarily raising of back feathers). Solar radiation also affected the frequency of heat avoidance. The study season was unusually wet and cool. In a more typical season heat avoidance may be more prevalent.
Photographs of Great Knots breeding in Russia seem to show more red feathering on the mantle and scapulars than is observed in birds fuelling in Australia. We studied the pre-breeding moult progression and plumage in knots before migration from Australia, just after arrival in China, and on Russian staging and breeding grounds (using specimens from the Zoological Museum of Moscow). Great Knots had either completed or suspended prealternate moult before departure from Australia, and birds caught after arrival in China had not resumed moult. Russian birds had greater numbers of red feathers on their upperparts. The difference between the plumage of Russian and Australian/Chinese birds could not be accounted for by the continuation of the prealternate moult. Instead, a presupplemental moult must occur in birds refuelling in the northern Yellow Sea. This is the third wader in which a presupplemental moult has been identified. The relative importance of sexual selection compared with natural selection in the evolution of this moult is unknown.
Great Knots were radio-tagged to determine individual departure dates on migration. When caught, condition indices were taken; body mass, breeding plumage score and breast muscle mass (estimated by ultrasound). Departures occurred evenly from 25 March to 13 April. Twenty-three of the twenty-seven radio-tagged knots departed on migration. Birds that remained had lower residual body masses and breeding plumage scores than birds that departed. Whether the birds that remained were off-schedule or subadult is not known. There was no relationship between body condition at capture and departure date for the birds that migrated. Departures from northwest Australia are still six to eight weeks before breeding starts, and time constraints probably become greater as birds migrate north towards the breeding grounds. These findings suggest that not all stages of a migration are under equally strong selection pressures.
Odum, E.P. et al. 1964. Science 143: 1037-1039
Pennycuick, C.R. 1998. Journal of Theoretical Biology 191: 47-61
Battley, P.F., A. Dekinga, M.W. Dietz, T. Piersma, S. Tang & K. Hulsman. 2001. Basal metabolic rate declines during long-distance migratory flight in Great Knots. Condor 103: 838-845.
Battley, P.F., M.W. Dietz, T. Piersma, A. Dekinga, S. Tang & K. Hulsman. 2001. Is long-distance bird flight equivalent to a high-energy fast? Body composition changes in freely migrating and captive fasting Great Knots. Physiological and Biochemical Zoology 94: 435-449.
Battley, P.F., T. Piersma, M.W. Dietz, S. Tang, A. Dekinga & K. Hulsman. 2000. Empirical evidence for differential organ reduction during trans-oceanic bird flight. Proceedings of the Royal Society of London, Series B 267: 191-195
Battley, P.F., T. Piersma, D.I. Rogers, A. Dekinga, B. Spaans & J. van Gils. 2004. Do body condition and plumage during fuelling predict northwards departure dates of Great Knots (Calidris tenuirostris) from North-west Australia? Ibis 146: 46-60.
Battley, P.F., D.I. Rogers & C.J. Hassell. 2005. Pre-breeding moult, plumage, and evidence for a presupplemental moult in the Great Knot. Ibis in press.
Battley, P.F., D.I. Rogers, T. Piersma, C.J. Hassell, A. Boyle & H.-Y. Yang. 2005. How do red knots (Calidris canutus) leave Northwest Australia in May and reach the breeding grounds in June? Predictions of stopover times, fuelling rates and prey quality in the Yellow Sea. Journal of Avian Biology in press.
Battley, P.F., D.I. Rogers, T. Piersma & A. Koolhaas. 2003. Behavioural evidence for heat load problems in Great Knots fuelling in tropical Australia for a northward flight of 5,500 km. Emu 103: 97-103.
Pennycuick, C.J. & P.F. Battley. 2003. Burning the engine: a time-marching computation of fat and protein consumption in a 5420-km flight by great knots Calidris tenuirostris. Oikos 103: 323-332.
Rogers, D.I., P.F. Battley, J. Sparrow, A. Koolhaas & C.J. Hassell. 2004. Treatment of capture myopathy in shorebirds: a successful trial in North-western Australia. Journal of Field Ornithology 75: 157-164.