Purple Martins are known for their nest fidelity. Once a Purple Martin settles on a nesting spot, it will likely travel back to that same nesting box for years to come. However, just because you've finally landed a colony of Purple Martins doesn't mean you're guaranteed to have them for a lifetime. Purple Martins often abandon their nesting sites due to a number of factors. Here are some things to be on the look out for.
Purple Martin Colony
Rival birds and other predators
Threats to Purple Martins come from two sources: rival birds and ground predators. Rival birds, such as the House Sparrow and the English Starling, will kill Purple Martins and their young and then take over their nests. The most crucial step in preventing this is to stop any rival birds from roosting in Purple Martin houses during the winter by plugging up the entrance holes. There are also a number of passive and aggressive methods that can be used to remove these birds, both of which are invasive species.
Predators such as raccoons, snakes, owls and other animals are also serious threats to a Purple Martin colony. In fact, one visit by one of these animals into a nesting box may dissuade Purple Martins from ever returning. Make sure to monitor you nesting box consistently for signs of intruders.
Trees and Shrubbery
Purple Martins spend most of their time in the air and require large expanses of space for swooping. If trees or bushes encroach upon a Purple Martin nesting space, they'll be less inclined to frequent it. Make sure to trim back encroaching trees and bushes on a regular basis.
Purple Martins are extremely sensitive to the weather. The primary reason for this is that their main food source is insects, who will completely disappear from the skies when extreme weather occurs. If inclement conditions continue for four or more days, Purple Martins will be in danger of starving. Extremely hot weather can also be dangerous to Purple Martin nestlings, which is why it's important to always ventilate nest boxes properly.
Purple Martins are susceptible to a number of parasites such as: black flies, blowflies, nest mites, flees and others. On occasion, infestations of nest mites can be so bad that Purple Martin parents refuse to enter the nest, resulting in the death of the nestlings. Once again, vigilant monitoring is the key to avoid such a problem. If you find a nest that's overrun with parasites, you can throw it out and replace it with dried grass or pine straw once the young have been alive for 13 days.
Not opening nesting boxes on time
Though Purple Martins are loyal to their breeding locations, they won't wait around forever for an owner to reopen nest boxes. If you see a group of Purple Martins congregating or hear their distinctive chatter, make sure their nest boxes are open and ready to be inhabited.
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