Carlos Esteban Lara, Benedikt Holtmann, Eduardo S. A. Santos, Shinichi Nakagawa 

The nestlings of many bird species have ornaments in their mouths (e.g., tongue spots), yet the within-species variation of these ornaments remains poorly explored. Here, we described a subtle and intriguing pattern of variation in the tongue spots of dunnock (Prunella modularis) nestlings and further evaluated their potential influence on parental feeding allocation. We observed that tongue spots in nestling dunnocks decrease along with nestlings aging and that tongue spots correlate with body condition, but the effects of nestling’s tongue spots on parental allocation were statistically unclear. This nature note invites further investigations into within-species variation of mouth marks in nestling birds, paving the way to a better understanding of these intriguing ornaments.