How many insects can a great tit population prey on in apple organic orchards? A modelling bioenergetics study

Orchards represent relevant study systems for investigating the functional role of insectivorous birds as regulators of pest insect populations. In this context, we used a bioenergetics model (Wiens and Innis, 1974) to estimate the seasonal variation in daily insect consumption by natural populations of the great tit (Parus major) in organic apple orchards. This model allowed us to estimate the changes in both adult densities and energy requirements in a P. major population, using field-measured parameters such as the brood size, and the length of incubation. The calculation of insect consumption rate by birds was based on both the existing literature on great tit diets and the simulated energy requirement of a great tit population. The effect of a temperature increase on energy requirement has been quantified. This study opens the way to consider the functional role of birds in agricultural landscapes and how this role may translate to ecosystem services.