A study of fasting in tree sparrows Spizella arborea and dark-eyed juncos Junco hyemalis ecological implications
Stuebe, M.M.; Ketterson, E.D.
Auk 99.2: 299-308
1982
ISSN/ISBN: 0004-8038 DOI: 10.2307/4085977
Accession: 037212617
Despite similarities in winter distribution, habitat selection, and food choice, Dark-eyed Juncos (Junco hyemalis ) and Tree Sparrows (Spizella arborea ) differ in the extent to which they store fat during winter, with juncos accumulating greater stores. Anticipating that Tree Sparrows might have some means of conserving energy during fasting and thus suffer no disadvantage when weather prevents feedings, the authors compared the species for weight loss, body temperature, and locomotor activity during fasting and noted relative fasting endurance. The species responded similarly to fasting by (a) lowering body temperature, especially at night, and (b) becoming hyperactive, progressively more so, as fasting time increased. Tree Sparrows did not exhibit these responses to a greater degree (although they became hyperactive sooner) and were not able to fast as long as juncos. No sexual differences in fasting ability were observed. Because the species-specific difference in tendency toward fat accumulation cannot be attributed to differences in energy expenditure while fasting, at least in the laboratory, other explanations are considered.