The role of birds in organic apple orchards: Opportunities for optimizing production and conservation
Worldwide, birds are a priority for conservation because they play an important role in natural and human-dominated communities. Declining bird populations can impact ecosystems, agriculture and the economy. Organic fruit farmers face many challenges but among the most impactful are insect and animal pests. Orchard birds have the potential to consume a major apple insect pest, the codling moth (Cydia pomonella), thereby reducing crop damage; however, birds also feed on the fruit. Our research examines these tradeoffs to better understand the connection between production and conservation. Specifically, our questions are: 1) which bird species contribute to insect pest control and fruit damage? and 2) what orchard or landscape features contribute to the rate and magnitude of these services and disservices?
To answer these questions, we are investigating foraging habits and fruit damage in three organic apple orchards near Paonia, Colorado. First, to determine the relative importance of fruit- and insect-consuming birds, we are observing the number of fruits damaged and time spent foraging, as well as collecting fecal samples from birds captured in mist-nets. Using DNA extraction, PCR and sequencing, we will determine the occurrence of codling moths in these samples. Second, we are using transect surveys to estimate occupancy and density of the birds determined to be important based on the first methods. Third, we are excluding birds from apples with nets and comparing levels of damage by birds and codling moths within and outside these exclosures. Finally, we are using these data to compare the rate and magnitude of pest control and damage as a function of location within the orchard, and surrounding land cover.
Preliminary results suggest that two bird species are contributing most to the damage, and that frugivory rates increase as fruits ripen. Pilot season results did not demonstrate significant differences in codling moth damage between apples inside and outside bird exclosures. Additional results are pending a second field season and continued analysis. Our study is designed to help farmers make better informed management decisions. For example, by identifying positive effects of birds, producers may have an incentive to protect or enhance habitat for species that are providing pest control services. In addition, by pinpointing times of high crop damage, farmers could focus bird control efforts temporally on targeted species. We plan to share our results with producers in a framework that helps them enhance both the economic and conservation value of apple orchards.