Yes — cucumber is mostly water: safe, hydrating, and low calorie.
Keeper's noteWet droppings afterward are normal — it's the water content. Wash the skin well or peel if waxed.
Why cucumber is good for parrots
Cucumber is about 96% water with mild amounts of vitamin K and potassium. It won't anchor a diet, but it's a refreshing, completely safe vegetable that suits overweight birds and hot days perfectly. Peel, seeds, and flesh are all fine.