All martin housing should be protected from both climbing and aerial predators. A martin house full of martins and their young is a tempting target for a variety of predators. It is easier to install poles guards to prevent rat snakes, raccoons and opossums from climbing up the poles than to modify housing or attached special guards to reduce predation by owls, hawks and crows. However, both poles and housing need to be protected from predators. Refer to the Problem Management section for instructions on how to protect martin housing from aerial and ground climbing predators.
Starlings are the deadliest nest competitors for martins.
Starlings will kill both young and adult martins inside the nesting compartments. Starling competition may become a big problem when martin landlords use large size nest compartments, as Starling prefer the bigger rooms for their bulky nests. However, there is now a way to eliminate the threat from Starlings with a specially designed entrance hole. You should consider using this hole design if Starlings are present at your colony site and have shown an interest in your martin housing. This hole will allow martins to enter but will exclude the vast majority of Starlings.