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Enlarged Compartments

Enlarging the nesting compartments is a choice of the landlord... here are some thoughts on the subject

In recent years the thought that larger nesting compartments for purple martins allowed them additional protection and better egg/fledgling production has become somewhat popular. Because their nest would be farther from the entrance, a predator reaching inside the nest compartment would not be able to reach birds in the back of the enlarged area as easily as in a standard 6"x6" compartment.

By enlarging compartments on Trio or DuraCraft aluminum martin houses, a dark cavity is created instead of the shiny interior of a 6"x6" compartment. This invites starlings, so a starling-resistant door must be used instead of a standard door. While this will prevent starlings from entering the compartment, sparrows can and will enter, and herein lies yet another problem. You must monitor houses that have been modified to 6"x12" compartments very closely (daily). It was soon discovered on our testing grounds that a sparrow will build a nest in front of an active purple martin nest trapping the martins in the compartment until they are discovered or die from starvation.

Supporters of large nest compartments claim a higher percentage success rate in fledging nearly all eggs that hatch. This can also encourage martins to lay more than the average of 4-5 eggs, to as many as 7 or 8 eggs. While we want to help the purple martin species flourish, two or three extra mouths to feed can overwork parents that sometimes struggle to keep a nest of four or five babies well fed, especially during inclement weather.

There are pros and cons to using enlarged compartments. Nature Society does not necessarily endorse the use of larger compartments, but offers instructions below to modify Nature House martin houses for those that prefer enlarged compartments. It should be noted that purple martins will rarely use starling-resistant doors on a standard house. Crescent doors will not be needed unless you have modified your martin house.

Conversion Instructions in PDF format: