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Living exposed and in the cold: thermostatic costs of nearctic knots (calidris canutus islandica) as measured by means of heated taxidermic mounts

Wiersma, P. (1991) Living exposed and in the cold: thermostatic costs of nearctic knots (calidris canutus islandica) as measured by means of heated taxidermic mounts. Master's Thesis / Essay, Biology.

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Heated taxidermic mounts calibrated under laboratory conditions with Nearctic Knots were used to estimate the relation between thermostatic costs (TC) of Knots in the field and ambient temperature, wind speed and global radiation, as measured by meteorological stations. Microhabitat and wind speed are the most important factors defining TC. Calibrations under forced convection conditions in the case of second year birds were significantly different from calibrations at still air. This however was not so for the adults, although the trend was the same. Below the lower critical temperature TC of adult Knots was 18% higher than that of second year Knots. The possible influence of the plumage colour could not be detected. By standing 90° on the wind direction up to 13% extra energy was lost compared with Knots standing faced to the wind. Heat loss from the feet was probably neglectable. Intake of cold food could result in an extra energy loss of maximally 0.19 W. TC could differ 100% due to the microhabitat. Densely vegetated salt marsh was 'cheapest' and standing on a bare ridge on the tundra resulted in the biggest heat loss. In order to estimate mean TC over periods longer than a day, it is allowed to use mean weather registrations, except under very warm conditions when TC exceeds a critical temperature. TC of an hypothetical Nearctic Knot flying on the Afrosiberian route would be 34% lower than when flying the original route. Possibly the two subspecies follow different strategies; the Afrosiberians spending less on TC than the Nearctic one, but possibly being adapted to the warm wintering conditions, or the Nearctics being adapted to the cold. To what extent this difference is reflected in the physiology of the subspecies is unknown, although mass specific BMR of Afrosiberian Knots seems lower than that of Nearctic Knots. Climatic data from the West-African wintering grounds shows that heat stress will not occur frequently.

Item Type: Thesis (Master's Thesis / Essay)
Degree programme: Biology
Thesis type: Master's Thesis / Essay
Language: English
Date Deposited: 15 Feb 2018 07:47
Last Modified: 15 Feb 2018 07:47

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