Protein supplementation decreases courtship rate in the zebra finch

Abstract

Much research has focused on the extent to which male ornaments and displays honestly reflect male quality or condition. While most ornaments are thought to be indicators of long-term condition, behavioural displays may be sensitive to short-term changes in condition. In the zebra finch, Taeniopygia guttata, male courtship rate has been suggested to be an honest reflection of male quality, yet experimental support for short-term condition dependence is limited. Captive zebra finches can be maintained on a seed-only diet, but dietary enrichment with high-protein food (hardboiled eggs) improves offspring growth, adult female fecundity and attractiveness. When given a choice, male zebra finches show a clear preference for such egg-supplemented seed mixture, presumably because of its greater richness in essential amino acids. Hence, we tested the hypothesis that male courtship rate can be increased by this nutritional enrichment. Contrary to our expectations, we found that this high-protein diet strongly reduced male courtship rate. We suggest two contrasting explanations for this counterintuitive finding. (1) The adult males’ preference for high-protein food might be maladaptive in captivity. Males may ingest too much protein, leading to reduced condition and courtship. (2) Nutritional enrichment may increase male condition, but courtship rate is not directly condition dependent. Instead, improved food quality might trigger a potentially adaptive shift in time allocation away from courtship and towards parental care. Follow-up studies will have to clarify whether this finding represents evidence for or against the condition dependence of courtship rate.