Development of nestling blue tits (Cyanistes caeruleus) is affected by experimental addition of aromatic plants

Abstract

Some passerines incorporate aromatic plants in their nest cups. These plants are hypothesized to i) reduce parasite loads, mitigating deleterious effects on nestlings (Nest Protection Hypothesis), ii) have positive effects on nestlings’ growth and body condition (Drug Hypothesis) and/or iii) play a role in mate attraction, reflecting a quality that may be beneficial to nestling rearing (Courtship Hypothesis). In this study we aimed to examine if experimental addition of aromatic plants had positive effects in reproductive performance (number of fledglings produced and nestling survival rate) and nestling body condition (weight and tarsus length). In addition, we study if those potential effects were more noticeable in different brood sizes - small and large - through an observational approach. No effect of treatment was observed in either reproductive performance or nestling condition parameters. However, a significant effect of year and brood size was observed regarding nestling weight while nestling tarsus length was improved in large broods of nests supplemented with aromatic plants.