You may want to think twice about poisoning your pigeon pests. Culling can effectively reduce pigeon numbers, but this is merely a temporary solution. After the culling process is complete, pigeon populations are known to rapidly return and can sometimes exceed pre-cull levels [Animal Aid]. Like many species, pigeons control their own population according to the food sources available. “Approximately 90% of pigeons die in their first year and the main cause of death is starvation. The mortality rate of adult pigeons is very low, typically around 11%. Therefore when culling is carried out on a pigeon population, the vacancies left by the dead birds are quickly filled by young birds” [Animal Aid]. Consequently, culling kills off adult pigeons allowing younger, sprucer, and more virile pigeons to survive, which would explain the post-cull population hike.
Instead of opting for short term solutions, such as culling, you may want to consider other humane, long-term bird repellent solutions. Popular bird repellent solutions are: