Chronic exposure to tebuconazole impairs offspring growth and survival in farmland birds: an experiment in captive house sparrows.

European farmland bird populations have declined by over 60% in 40 years, with the use of pesticides suspected to be one of the main causes of this decline. However, it remains difficult to test the impact of these pesticides in field studies due to confounding environmental variables that can also affect avian wildlife (e.g., food resources, habitat fragmentation and alteration). Triazoles are a family of fungicides that are ubiquitous in agro-ecosystems due to their use on a wide range of crops. Triazoles are suspected to affect non-target avian species by disrupting key physiological mechanisms and by detrimentally affecting their reproduction. In this captive study, we experimentally investigated the effect of the most commonly used triazole fungicides (i.e., tebuconazole) on the reproduction of an avian species representative of farmlands, the house sparrow (Passer domesticus). We examined the impacts of tebuconazole at realistic concentrations (550 μg.L in drinking water to achieve ∼ 60 pg.g in plasma of sparrows) under controlled conditions on multiple indicators of breeding performance (clutch size, hatching success, chick growth and survival). We found that chronic exposure to tebuconazole (9 months, including the breeding period) significantly altered the reproduction of sparrows. Although clutch size and hatching success were not affected by tebuconazole, chicks from the exposed group showed reduced growth and a higher mortality rate. Interestingly, these effects were exacerbated in female chicks, highlighting a sex-dependent effect of tebuconazole on sparrow offspring. This study demonstrates that tebuconazole can be detrimental to the reproduction of farmland birds. Further studies are now required to distinguish the direct effects of tebuconazole (toxic and sublethal effects on the developing chick/embryo) from the indirect ones (alteration of egg quality and parental care).