Energetics of Altricial Nestlings in Cold Climates: Insights from the Mountain White-Crowned Sparrow

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[edit] Author(s)

  • Weathers, W. W.
  • Davidson, C. L.
  • Morton, M. L.

[edit] Journal

Condor 105.4 (2003): 707-18.

[edit] Keywords

energetics growth nestling white-crowned sparrow zonotrichia leucophrys oriantha doubly labeled water energy-requirements parental effort growth-rate temperature validation chicks birds

[edit] Abstract

We determined the energy budget of nestling Mountain White-crowned Sparrows (Zonotrichia leucophrys oriantha) at a 2900-m-high subalpine site by combining growth data with measurements of field metabolic rate (doubly labeled water technique) and resting metabolic rate made on different-aged nestlings. Nestling sparrows grow rapidly (their logistic growth rate constant is 129% of the allometric prediction) and they fledge at 9 days of age weighing 20.6 g (75% of adult mass). Relatively rapid growth in a cool montane environment (mean daytime air temperature = 16.5 +/- 1.4degreesC) is associated with high daily and total nestling energy requirements. During the 9 days between hatching and fledging, each nestling metabolized a total of 443 U of energy; a value 25% higher than expected for an open-nesting passerine bird. The relative cost of producing a fledgling White-crowned Sparrow (21.5 kJ per g body mass) exceeds that of the three other open-nesting passerine species that have been measured with doubly labeled water (range 16.5-19.3 U g(-1)). The energy that nestling sparrows accumulated as new tissue (115 kJ) constituted 26% of the total energy metabolized; substantially less than the 37% allocated to activity and thermoregulation combined. Nestling White-crowned Sparrows allocated more energy to activity and thermoregulation than nestlings of most other parent-fed species, but much less than the 50-53% of total metabolizable energy allocated by precocial shorebird chicks.

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