Tongue spots of Dunnock (Prunella modularis) nestlings reflect body condition but exert only conditional influence on parental allocation

Abstract

The nestlings of many bird species have ornaments in their mouths, yet the within‐species function of these ornaments remains relatively little studied compared with adult ornaments. Here, we describe the pattern of variation in the tongue spots of Dunnock Prunella modularis nestlings and evaluate their potential influence on parental allocation. We observed that some nestlings hatch with a third tongue spot at the tip of the tongue, which then fades as nestlings age. The number of tongue spots present is inversely related to nestling weight, but the number of tongue spots present does not appear consistently to influence parental allocation. This suggests the need for further investigations into within‐species variation of mouth marks in nestling birds to pave the way to a better understanding of these intriguing ornaments.