Mechanisms promoting higher growth rate in arctic

Authors: Hans Schekkerman Ingrid Tulp Theunis Piersma G Henk Visser

Publish Date: 2002/12/18

Volume: 134, Issue: 3, Pages: 332-342

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Abstract

We compared prefledging growth energy expenditure and time budgets in the arcticbreeding red knot Calidris canutus to those in temperate shorebirds to investigate how arctic chicks achieve a high growth rate despite energetic difficulties associated with precocial development in a cold climate Growth rate of knot chicks was very high compared to other mainly temperate shorebirds of their size but strongly correlated with weatherinduced and seasonal variation in availability of invertebrate prey Red knot chicks sought less parental brooding and foraged more at the same mass and temperature than chicks of three temperate shorebird species studied in The Netherlands Fast growth and high muscular activity in the cold tundra environment led to high energy expenditure as measured using doubly labelled water total metabolised energy over the 18day prefledging period was 89 above an allometric prediction and among the highest values reported for birds A comparative simulation model based on our observations and data for temperate shorebird chicks showed that several factors combine to enable red knots to meet these high energy requirements 1 the greater coldhardiness of red knot chicks increases time available for foraging 2 their fast growth further shortens the period in which chicks depend on brooding and 3 the 24h daylight increases potential foraging time though knots apparently did not make full use of this These mechanisms buffer the loss of foraging time due to increased need for brooding at arctic temperatures but not enough to satisfy the high energy requirements without invoking 4 a higher foraging intake rate as an explanation Since surfaceactive arthropods were not more abundant in our arctic study site than in a temperate grassland this may be due to easier detection or capture of prey in the tundra The model also suggested that the coldhardiness of red knot chicks is critical in allowing them sufficient feeding time during the first week of life Chicks hatched just after the peak of prey abundance in midJuly but their food requirements were maximal at older ages when arthropods were already declining Snow cover early in the season prevented a better temporal match between chick energy requirements and food availability and this may enforce selection for rapid growthPetra de Goeij Jan van de Kam and Joop Jukema provided indispensable help during fieldwork with further assistance from Hans Dekkers and Valeri Bozun Berthe Verstappen CIO skilfully performed the isotope analyses The project was financed by the Dutch Ministry of Agriculture Nature Management and Fisheries Netherlands Institute for Sea Research NIOZ Netherlands Organisation for Scientific Research NWO Stichting Plancius Lund University and c 80 individual private benefactors Logistic help was provided by the Institute of Evolutionary Morphology and Animal Ecology Russian Academy of Sciences staff of the Great Arctic Reserve and by Gerard Boere Bernard Spaans Bart Ebbinge and Gerard Müskens The manuscript benefited from comments by Bruno Ens Rudi Drent Arie Spaans and Eric Stienen This is NIOZpublication 3599The simulation model predicts body mass foraging time energy requirements and required metabolisable energy intake of red knot and common redshank chicks during an 18day fledging period on the basis of growth time budget and metabolism data reported in this paper or from the literature We distinguished two environments differing in daylength D h/day and operative temperature T e °C arctic D=24 h/day T e=3°C data from Cape Sterlegov and temperate D=16 h/day T e=15°C data from The Netherlands May–June 1992–1995

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