Authors: Müller, Jörg; Mitesser, Oliver;Hochrein, Sophia;Weisser, Wolfgang;

Rachel Carson's warning of a silent spring by an absence of songbirds due to pesticides led finally to a US-wide ban on DDT in the 1970s. Nevertheless, multiple anthropogenic stressors have continued to increase in global ecosystems, which makes the identification of mechanisms for population declines in observational studies increasingly difficult. We tested the effect of aerial tebufenozid-applications to control a defoliating moth in hyper-diverse oak forests on birds, using autonomous sound recorders in a large replicated full factorial field experiment. Over the period of our three-year study, we found significantly reduced acoustic complexity in early summer during the first two years because of pesticide-application. However, a deeper evaluation showed that this reduction in acoustic complexity was not related to birds, but to a reduction in the caterpillars' chewing sounds. The several year approach showed that the legacy of the pesticide treatment lasted for a second year, but occurred consistently in the same phenological time window. Our study show that continuous measurements of sound diversity are able to identify even cryptic changes in the environment just by acoustic changes. However, the pesticide application did not affect the sound activity of birds as originally expected.