Birds eavesdrop on plant indirect defenses to locate insect preys

Methods

Summary

Deploying dispensers and fake insects

Dispenser containing an odor blend and solvent will be attached on a small stake (0.5 cm diameter) at 1 m from the ground with white masking tape. Ten fake larvae (made with 10 g of dark green Scupley clay) will be pinned (orange head pin, mimicking the caterpillar head capsule) on similar stakes (2x0.5 m, 2x1 m, 2x1.5 m high, respectively) randomly distributed in 5 m radius around the stake holding the volatile dispenser. In the forest environment, the stakes height will be increase by 0.5 m to better reflect the vegetation structure.  In total, this set-up will be replicated 8 times per environment. The replicates will be at least 20 m apart. Control will be set similarly but the dispensers will contain solvent only. The experiment will last three weeks.

Predation of fake insects

To evaluate bird predation of fake insects, each site will be visited weekly and fake caterpillars will be visually assessed for predation marks. Predated insects will be replaced by new undamaged caterpillars. The number of predated insects as well as the number of bird peck per insects will be recorded.

Bird pictures

Two camera will be deployed per environment. The cameras will be attached on metal stakes at the same height as the dispensers. Each camera will cover one area encompassing one dispenser and ten fake insects. The time laps camera will be set to take a picture every 30 s dawn to dusk. SD cards and batteries will be change weekly. At the completion of the experiment, the pictures will be downloads and visually checked for the presence of birds. The species and number of predation events will be recorded.