Tree Sparrow nests as indicators of plastic pollution in anthropized environments

Abstract

Nowadays, plastic stands out as one of the most widespread pollutants in natural environments. While much research has focused on plastic pollution in marine ecosystems, it is essential to recognize that plastic also affects terrestrial ecology. Birds, which construct nests using a variety of locally available materials, are not exempt from this influence, as they sometimes incorporate plastics of human origin into their nesting materials. This study aims to investigate whether the tendency to include such anthropogenic materials also extends to birds that build nests in enclosed spaces, such as nest boxes. To explore this, we examined a total of 11 Tree Sparrow nests, categorizing the materials used and paying particular attention to those derived from human activities, especially plastics. In addition, we analyzed whether the birds exhibited preferences for specific colors and types of anthropogenic materials when constructing their nests, which could be influenced by the availability of these materials in the local environment. Our findings revealed that plant-based materials were the primary components of the nests, followed by animal-derived and anthropogenic materials. Notably, anthropogenic materials were present in all the nests examined. Interestingly, there appeared to be a distinct preference for black and filamentous anthropogenic materials over other types and colors. This suggests that tree sparrows may be selective in their use of human-made materials—possibly due to factors such as local availability, physical properties like durability, or resemblance to naturally occurring materials.