Differences between the outer and inner structure of the Short-toed treecreeper’s (Certhia brachydactyla Brehm, 1820) nest in an urban area

We reported the first available data on the fine-grained structure of the short-toed treecreeper’s (Certhia brachydactyla Brehm, 1820) nest located in an urban park of Rome (central Italy). The outer structure was characterized by a high percentage of conifer (Pinus pinea) needles, which are significantly longer than other branches and twigs. Pine needles are widely available in urban parks, and being more flexible and easily detachable, may contribute to the support of the outer nest structure provided by other linear components (i.e., twigs/branches). Moreover, their aromatic terpenes may control nest parasites. In contrast, the internal cup lining was composed of a very light and heterogeneous set of components (bird feathers of at least one synanthropic bird species: Streptopelia decaocto), vegetable fluff, grass leaves, shrubs and trees, moss, sand, dust, and plant roots, i.e., all the materials largely used in bird nests because of their insulative qualities and thermoregulation functions. Although the internal cup lining was more heterogeneous in composition, the total weight of the outer nest was significantly heavier (>65% on the total nest weight).