If the housing they are used to is gone or significantly altered, they may choose to abandon the site. If you wish to add or replace housing, it is best to put the new housing up close by for a season before removing the older housing. This gives the martins an opportunity to get used to the new housing and increases the chances for occupancy in the following year. Landlords with several houses can replace housing between seasons without risk of colony loss. The most common reason purple martins abandon there nesting sites is predation.
Predators can include owls, snakes, raccoons, hawks, crows, or even squirrels.
A pole predator guard should always be used. Note that larger compartments can add extra protection from aerial predators such as owls and hawks.