To cure and / or protect clients from mental and physical illness caused by spirits and individual forces, Yoruba diviners (babalawos) enlist the help of Osanyin, the god of divination or Erinle, the god of herbal medicines. According to Babatunde Lawal, Osanyin is seen as "the one who sees everything like Olodumare, allowing him a vantage point from which he can protect all of humanity below".1 It is believed that an iron staff, opa osanyin (also called opa erinle), holds the power of Osanyin & Erinle. This staff is placed on Osanyin altars and is used during the divination process to cure afflictions (usually placed in the ground next to the afflicted person).
The Yoruba believe that a large bird surrounded by smaller birds symbolises the power of good over evil and the ability to control spirits and supernatural forces. As such opa osanyin physically represents this power: one large bird is typically surrounded by 16 smaller birds at the summit of the staff. The smaller birds represent witches; these witches can transform themselves into birds to support the healing process for Erinle. "The number of encircling birds, sixteen, is fundamental to Yoruba numerology; it is basic to the divination system, and is the original number of Yoruba kings."2
It is unclear what the central large bird represents. Several sources point to the large central bird representing Osanyin while others cite the central bird as representing Orunmila ('the grand priest and custodian of the Ifa Oracle', i.e. the Orisha of wisdom, knowledge and divination).3 It is believed that Orunmila is the source of all knowledge and is believed to have a good understanding of the human form and to cure illness and deformities.4 A final source points to the bird representing Ogun, the god of iron.5