Declining food availability alters vocal behavior of a nomadic finch

Social information (i.e., gathered from other individuals) can be an important information source for animal decision-making related to foraging and movement. For instance, social information in the form of acoustic cues can be used to locate food sources. The ability to accurately assess declines in food availability or quality in order to make movement decisions can also impact fitness. However, little is known about whether the acoustic cues produced by animals differ when food is in decline and could therefore be used as a source of information in this context. To test this hypothesis, we conducted a study on the effect of food availability on the vocal behavior of pine siskin (Spinus pinus). Pine siskins are gregarious, nomadic finches that feed on seeds that fluctuate irregularly and dramatically in abundance. We recorded and characterized the vocalizations of wild-caught birds in captivity under two experimental conditions: unlimited food and a 20% reduction in food availability. Birds called more frequently when food restricted and increased the production of two specific call types (Types B and C). For both of these call types, the minimum frequency was higher when birds were food restricted, and for C calls the median, peak dominant, and peak fundamental frequencies were also higher. We further tested whether changes in acoustic frequency were associated with circulating corticosterone levels, as is predicted by the hypothesis that circulating glucocorticoid levels mediate changes in acoustic frequency in response to food restriction, and found only limited evidence to support the hypothesis.