High Levels of Energy Expenditure in Shorebirds; Metabolic Adaptations to an Energetically Expensive Way of Life

  • Kersten M
  • Piersma T
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Abstract

We measured basal metabolic rate (BMR), existence metabolism (EM) and costs of thermoregulation in three species of captive shorebirds. Oystercatcher, Grey Plover and Turnstone. In all three species BMR was above the values predicted from their body weight (Aschoff & Pohl, 1970). Including results of other studies, BMR of six shorebird species ranging in body weight from 36 g to 543 g, was on average 42% above the predicted level for a non-passerine. EM and DEE (daily energy expenditure) were relatively high as well. However, the ratio between BMR on the one hand and EM and DEE on the other, were not unlike those in other bird species, i.e. 2 and 3 times BMR respectively. We hypothesize that a high DEE, mainly generated by the skeletal muscles, requires a high level of support by the organs in the abdominal cavity, which inevitably results in a high BMR. This interpretation provides a functional explanation for the constant ratio between BMR and DEE in many bird species and explains the existence of a 'maximum sustained working level' (Drent & Daan 1980) of parent birds feeding their young at approximately four times BMR. We suggest that the high DEE of temperate wintering shorebirds must be considered in relation to peak energy demands during their annual cycle. Candidate times are the periods of pre-migratory fattening and mid-winter. The captive birds showed annual fluctuations in body weight associated with premigratory fattening, resembling those of their conspecies in the wild. From the measurements of food intake we estimated the additional amount of energy needed for a 1 g increase in body weight at 45.66 kJ. Using this value, we estimate the efficiency of energy deposition at 88%. Food intake increased with average body weight in all captive groups, but the BMR of an individual Turnstone did not, suggesting that fat has a low metabolic activity.

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Authors

  • Marcel Kersten

  • Theunis Piersma

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