How big should the entrance hole be for martins?
According to most specification sheets available on this subject, the entrance hole for purple martins can be anywhere from 1 3/4″ to 2 1/4″ in diameter. Most commercial houses are sold with the 2 1/8″ holes in them. If you’re building your own, then the decision for the entrance hole is yours. However, Please Note: Because of the recent increase and infestation of European Starlings, it is now highly recommended that these round holes be changed to crescent shaped Starling Resistant Entrance Holes (SREH). A lot of testing went into a couple of different shapes to create an entrance hole that would keep starlings out of martin housing, one being the oblong, the other, crescent. It was found that in many cases, starlings could negotiate the oblong and that shape was quickly eliminated as a martin entrance hole. However, the crescent shaped hole (shown below) has proven to be very effective as a deterrent for starlings and is quickly becoming the new standard for entrance holes for purpl
