Are microbes and metabolites influencing the parental consumption of nestlings’ feces in gray-backed shrikes?

Abstract

The behavioural video recordings of the grey-backed shrike Lanius tephronotus revealed that parent birds eat the faeces produced by their nestlings. ‘Parental nutrition hypothesis’ attributes the origin of this behaviour to nutrition-recovery and cost-saving, respectively. However, the presence of usable nutrients in the nestlings’ faeces is unknow because of traditional technology. In this study, we analysed all the metabolites and the variations in the diversity and content of microbes in the faeces of grey-backed shrike nestlings. We aimed to report the changes in microbes and metabolites with the age of nestlings and point out that the parent birds that eat the faeces may gain potential nutrition benefits. The results showed that the relative abundances of Proteobacteria, Firmicutes, and Bacteroidota, changed significantly when the nestlings were six days old. The relative abundances of six probiotics, which are involved in digestion, metabolism, and immunity-related physiological functions, decreased in the nestlings’ faeces gradually with age; therefore, these probiotics may be obtained by parent birds upon ingestion of the faeces of young nestlings. Among the metabolites that were detected, 20 were lipids and some had a role in anti-parasitic functions and wound healing; however, their relative contents decreased with age. These beneficial substances in the nestlings’ faeces may stimulate the parents to swallow the faeces. Moreover, there were many aromatic metabolites in the newly hatched nestlings’ faeces, but the content of bitter metabolites increased as they grew up. Therefore, our results are in accordance with the nutritional hypothesis.