To date, the contribution of pesticides to the decline of farmland bird species is still controversial. Most studies interested in the effect of agrochemicals are limited to the assessment of the lethal dose 50 (LD50) and tested on a restricted number of model species. They often ignore the delayed effects on the physiology, the behaviour and the life history traits of the individuals, and their evolutionary consequences at the population level. Understanding and quantifying such effects is fundamental for our knowledge of the avian population decline. With PestiStress, I aim at investigating the effects of realistic pesticide cocktail through two complementary approaches, an experimental design in controlled conditions and the monitoring of a natural population, on two farmland flagship species, the Grey partridge (Perdix perdix) and the Montagu’s harrier (Circus pygargus). Especially, the emphasis will be put on neonicotinoid insecticides and on glyphosate-based herbicides, both being supposed to be banned by September 2018 and 2021 in France respectively. PestiStress will provide a first assessment of the effects of these pesticides on avian wildlife fauna by an integrative methodology that involves physiology, behaviour and life history traits. I will also for the first time investigate the transgenerational impact of the pesticides under natural exposure. Finally, the data collected during PestiStress will be used to model population dynamics to decipher the importance of long-term effects for conservational purpose in Montagu’s harrier. In the current societal context in regard to the use of pesticides and their effects on biodiversity and human health, PestiStress will provide new insights that will contribute to one of the major societal challenge in Agroecology for this century.