Drivers of irrigated olive grove expansion in Mediterranean landscapes and associated biodiversity impacts

•Area of irrigated olive groves greatly increased in Southern Portugal in 1990–2017.•Irrigated groves mostly replaced open dry farmland (63%) and traditional groves (21%).•Availability of irrigation water on large farms boosted transitions to irrigated groves.•Transitions to irrigated groves had the worst impacts on farmland birds.•Further expansion of irrigated groves in biodiversity-rich farmland should be prevented.