lphachloralose - this poison is usually given to pigeons in the form of treated grains. You should first feed them with grains that are not poisoned for a few days, so as to attract more pigeons to the feeding spot. Alphachloralose makes them feel stupor-like and they later die. With this mechanism however, they are highly likely to die in unwanted places, like where scavenging wildlife or domestic animals will feed on the carcass and get poisoned too.
Avitrol – it contains 4-aminopyridine, which is a central nervous system toxicant. It causes convulsive reaction for hours and in pigeons, it is characterized by falling and flapping before finally giving up the ghost. Though effective in killing pigeons, it can as well kill other animals, so watch out for neighborhood pets.
Thallium - this composition can be administered to pigeons through inhalation or oral consumption. It is a tasteless poison that can be mixed with their feeds or even dissolved in water. Thallium induces nausea, vomiting and pain before killing them.
Antifreeze - another deadly remedy commonly used in killing pigeons.
Aside from Antifreeze, I'm not sure how available the other chemicals are here in the DR.