White-tailed ptarmigan food calls enhance chick diet choice: learning nutritional wisdom?

Abstract

Social learning is predicted to be adaptive when independent learning is time-consuming, dangerous or difficult. For a naïve individual confronted with an array of novel foods, determining the nutritional value of unfamiliar foods can be challenging, and an increased reliance on social learning would be favoured by selection. I investigated whether the multimodal display of food calling and tid-bitting by white-tailed ptarmigan, Lagopus leucurus, hens adaptively biases chicks' intake of foods of different nutrient content via social learning. Ptarmigan were observed in California's Sierra Nevada alpine for two summer seasons. In 116 foraging bouts, I observed 100 instances of hen food calling (to six plant species) and 100 responses by chicks. The relative proportion of each plant species in the chicks' diet was significantly and positively related to the proportion of food calls associated with that plant species, but not with its relative availability. Plant species that elicited food calls by hens had significantly more protein than did random mixtures of plants or than did foods eaten by the hens that did not elicit food calls. Chicks of hens that often uttered calls consumed diets significantly higher in protein than did chicks of hens that rarely called. Preferences were maintained as chicks became older and foraged further from their mothers, and food calling ceased, indicating social learning. Hens' food calling biased chicks' diet choices, supporting the prediction that socially acquired information plays a prominent role when an animal is seeking a nutrient that is difficult to identify (protein). These findings are consistent with the interpretation that ptarmigan hens engage in teaching, but further studies are required before it can be stated conclusively that they teach their chicks nutritional wisdom.