Role of birds in biosecurity of urban trees and forests

This project will evaluate the contribution of birds in the regulation of invasive insect pests and the potential spread of tree pathogens in urban areas. Insectivorous birds are known to be important predators of insects, and this includes several invasive insect species that cause tree damage or mortality. Bird predation may represent a significant barrier for invasive insects, potentially reducing their likelihood of establishment or regulating population sizes.

The knowledge gained in this project will help guide decisions about future urban tree composition and cover to improve invasion resistance and control of pests and pathogens in European cities. Our specific aims are to assess in different urban tree settings:
      (I)     the composition of bird assemblages in relation to tree cover and species composition,
      (II)    predation pressure of birds on insects,
      (III)   the presence of invasive insect DNA in urban bird faeces,
      (IV)  the prevalence of pathogen spores on the external body parts of birds.

To address these aims, the project will implement an experimental design to sample birds in urban sites differing in tree cover, tree species composition, and bird species composition. This will be replicated across three Swiss cities: Zurich, Basel, and Lugano. Using a replicated systematic treatment design, we will

• conduct bird surveys using standard transect counts,
• use tethered artificial model caterpillars and naturally occurring invasive insects to determine attack rates by birds,
• capture birds to collect swab and faecal samples for analysis of insect and pathogen DNA using molecular techniques.

The presence of insect pest species and tree pathogens in the faecal and swab samples, respectively, will reveal to what extent birds act as predators that contribute to the control of insect pests and whether they play a role as potential pathogen vectors to urban trees.