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 Phil F. Battley, Danny I. Rogers, Jan A. van Gils, Theunis Piersma, Chris J. Hassell, Adrian Boyle and Yang Hong-Yan Battley, P. F., Rogers, D. I., van Gils, J. A., Piersma, T., Hassell, C. J., Boyle, A. and Yang, H.-Y. 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.  / J. Avian Biol. 36: 494 /500. In general, Arctic-breeding waders leave non-breeding grounds in Australasia from March (New Zealand) to mid-April (Northwest Australia). Here we provide evidence from radio-tracking and visual observations that many red knots Calidris canutus do not leave Roebuck Bay, Northwest Australia, until early or mid-May. Late-departing red knots probably belong to the subspecies piersmai , which breeds on the New Siberian Islands, 10,400 km from Northwest Australia. Based on comparisons of temperatures on the breeding grounds of different knot subspecies, we predict that piersmai knots would not arrive on the breeding grounds until early June, leaving at most 3  /4 weeks refuelling in Asia. Using a model of fuelling capacity in relation to prey quality and gizzard mass, we show that these knots must fuel very differently in Australia and Asia. In Australia, knots have seemingly suboptimal gizzard sizes and deposit fuel slowly. In the Yellow Sea, birds could only fuel up within the available time if they either enlarged their gizzards substantially or encountered prey qualities much higher than in Australia, for which we provide quantitative predictions. Phil F. Battley (correspondence), Australian School of Environmental Studies, Griffith University, Nathan, Queensland 4111, Australia. E-mail: philbattley@quicksilver.net.nz. Danny I. Rogers, School of Environmental and Information Sciences, Charles Sturt University, P.O. Box 789, Albury, NSW 2640, Australia. Jan A. van Gils and Theunis Piersma, Animal Ecology Group, Centre for Ecological and Evolutionary Studies, University of Groningen, P.O. Box 14, 9750 AA Haren, The Netherlands, and Department of Marine Ecology and Evolution, Royal Netherlands Institute for Sea Research, P.O. Box 59, 1790 AB Den Burg, Texel, The Netherlands. Chris J. Hassell and Adrian Boyle, P.O. Box 3089, Broome, West Australia 6725, Australia. Yang Hong-Yan, Key Laboratory of Ministry of Education for Biodiversity and Ecological Engineering, College of Life Science, Beijing Normal University, 100875, Beijing, China. Present address of PFB: Department of Mathematics and Statistics, Otago University, P.O. Box 56, Dunedin, New Zealand. Present address of JAvG: Netherlands Institute of Ecology (NIOO-KNAW), Centre for Limnology, Rijksstraatweg 6, 3631 AC Nieuwersluis, The Netherlands. Timing of arrival on the breeding grounds may be critical to the breeding success of individual birds, and places a premium upon the appropriate timing of migration. Waders that breed in the Arctic but winter in the Southern Hemisphere can start pre- paring for northwards migration as early as January or February, and typically depart in March and April (Tulp et al. 1994, Battley 1997). Species undertaking long flights generally have at least one refuelling stopover en route to the breeding grounds, while species making shorter flights may have several. # JOURNAL OF AVIAN BIOLOGY JOURNAL OF AVIAN BIOLOGY 36: 494  /500, 2005 494 JOURNAL OF AVIAN BIOLOGY 36:6 (2005)