The idiom is “To have bats in the belfry” means to be crazy or eccentric. This expression may come from the idea that bats might inhabit the bell tower or belfry of a church, and their erratic flight patterns might make them appear crazy. Another explanation is that the word “bats” is derived from the word “batty” ( slightly crazy) .The phrase refers to anyone who exhibits strange or unconventional behaviour, often in a humorous or light-hearted way.
In Spanish, the equivalent expression is “Tener pájaros en la cabeza,” which translates to “To have birds in your head.” This idiom is also used to describe someone who is perceived as being crazy or eccentric. The imagery of birds nesting in someone’s head is quite vivid and memorable, making this idiom an effective way to convey the idea of unconventional behavior.