Shivering and Heat Production in Wild Birds

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Abstract
Shivering responses of 4 species of wild birds (evening grosbeak, Hesperiphona vespertina; common redpoll, Acanthis flammea; common grackle, Quiscalus quiscula; common crow, Corvus brachyrhynchos) were assessed in response to environmental temperature by measuring the electrical activity of the pectoral muscles. Shivering increased linearly with decreasing temperature below 30[degree]C in all species. No thermoneutral zone was indicated below 30[degree]C. It is concluded that most wild birds with body weights below 350-400 must shiver when inactive at environmental temperatures normally encountered in north temperate, subarctic, and arctic regions. Evening grosbeaks acclimated to constant temperatures of 18[degree], 10[degree], and -15[degree]C showed no differences in levels of shivering at various temperatures. Grosbeaks acclimatized to winter and summer seasons likewise exhibited no difference in level of shivering at -10[degree]C. A linear correlation of shivering with oxygen consumption was found for all 4 species studied. The species correlations tend to be colinear when oxygen consumption is expressed on a surface area basis. There is no indication of nonshivering thermogenesis occurring and it is concluded that shivering and muscular activity are the principal means of extra heat production in birds.