Winter fattening in the American goldfinch and the possible role of temperature in its regulation

Dawson, WR.; Marsh, RL.

doi:10.2307/30156107

We investigated whether environmental temperature has any causal role in the winter fattening in certain finches of the subfamily Carduelinae. Correlational analyses between fat content of American goldfinches (Carduelis tristis) and various short- and long-term measures of temperature provide no evidence for a proximate role of this environmental variable in determining the degree of fattening of these birds in southeastern Michigan USA . Their fat content shows the best correlations (r = -.61 to -.63) with the long-term average minimum temperature or record low temperature for the date of capture. Furthermore, inclusion of long-term thermal measures in multivariate analyses excludes from significance temperature conditions surrounding the day of capture. Comparison of American goldfinches wintering in Michigan, California, and Texas, respectively, strengthens the conclusion that environmental temperature does not directly influence their fat content. Taken together, our data on this species favor the hypothesis that temperature is an ultimate, i.e., evolutionarily significant, rather than a proximate factor in winter fattening. Comparisons of American goldfinches, pine siskins (Carduelis pinus), and common redpolls (Carduelis flammea) in Michigan indicate that these similar-sized congeners show different levels of winter fattening under similar winter conditions. The differences in fat content among these species do not correlate in any simple way with their respective overall winter distributions.