Seasonality in basal metabolic rate and thermal conductance in a long-distance migrant shorebird,the knot (Calidris canutus) |
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Authors: | T Piersma N Cadée S Daan |
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Institution: | (1) Zoological Laboratory, University of Groningen, P.O. Box 14, NL-9750 AA Haren, The Netherlands;(2) Netherlands Institute for Sea Research (NIOZ), P.O. Box 59, NL-1790 AB Den Burg, Texel, The Netherlands;(3) Present address: Zoological Institute, University of Copenhagen, Universitetsparken 15, DK-2100 Copenhagen, Denmark |
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Abstract: | Knots Calidris canutus live highly seasonal lives, breeding solitarily on high arctic tundra and spending the non-breeding season in large social
flocks in temperate to tropical estuaries. Their reproductive activities and physiological preparations for long flights are
reflected in pronounced plumage and body mass changes, even in long-term captives of the islandica subspecies (breeding in north Greenland and northeast Canada and wintering in western Europe) studied in outdoor aviaries.
The three to four fattening episodes in April-July in connection with the flights to and from the high arctic breeding grounds
by free-living birds, are represented by a single period of high body mass, peaking between late May and early July in a sample
of ten captive islandica knots studied over four years. There are consistent and synchronized annual variations in basal metabolic rate and thermal
conductance in three islandica knots. Basal metabolic rate was highest during the summer body mass peak. Within the examined individuals, basal metabolic
rate scales on body mass with an exponent of about 1.4, probably reflecting a general hypertrophy of metabolically expensive
muscles and organs. Any potential effect of moult on basal metabolic rate was obscured by the large seasonal mass-associated
variations. In breeding plumage, insulation (the inverse of thermal conductance) was a factor of 1.35 lower than in winter
plumage. This was paralleled by the dry mass of contour feathers being a factor of 1.17 lower. In this subspecies the breeding
season is indeed the period during which the costs of thermoregulation are lowest. In captive knots seasonal changes in basal
metabolic rate and thermal conductance likely reflect an anticipatory programme adaptive to the variable demands made by the
environment at different times of the year. |
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Keywords: | Basal metabolic rate Thermal conductance Physiological adaptations Annual rhythms Bird migration |
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