Purple martins are beautiful swallows that live across North America. They are the largest species of swallow in North America. Purple martins migrate long distances and nest in colonies, making them a delight to observe in the summer months. However, purple martins face threats from predators. As human development encroaches on their habitat, it becomes more important to take steps to protect purple martins from predators. This article will provide an overview of purple martin biology and behavior, threats from predators, and techniques to protect purple martins.
Purple Martin Biology
Purple martins are members of the swallow family Hirundinidae. They have dark blue-purple feathers on their back and wings that shimmer in the sunlight. Their underside is a lighter gray color. Males have darker plumage that shines more brightly than females. Purple martins have a forked tail and long, pointed wings. Their beaks are small and suited for catching insects in flight.
Purple martins are neo-tropical migrants that breed in North America and winter in South America. They migrate thousands of miles each spring and fall between their breeding and wintering grounds. Purple martins arrive back to their breeding grounds starting in January in the southernmost parts of their range. They continue to arrive farther north into March, April and May.
Purple martins are colonial cavity nesters. They nest in abandoned woodpecker cavities, natural cavities, or man-made nest boxes placed in clusters called “martin houses.” Colonies can contain just a pair of birds up to hundreds of breeding pairs. Purple martins may reuse the same cavity year after year. The female lays 3-6 eggs and incubates them for 15-18 days while the male provides food. Both parents feed the nestlings until they fledge 26-32 days after hatching.
Diet
Purple martins are aerial insectivores, meaning they catch all their prey mid-flight. They do not land to catch insects on the ground. Purple martins feed on a wide variety of flying insects including dragonflies, damselflies, flies, moths, butterflies, bees, wasps, flying ants, and ballooning spiders. The diet shifts based on time of day, weather, season, and location.
Threats from Predators
Purple martins face predators at their roosting and nesting sites. Predation is one of the primary threats to purple martin survival and productivity. The main predators of adult purple martins, eggs, nestlings and fledglings include:
Hawks
Sharp-shinned hawks, Cooper’s hawks, and merlins will prey on adult purple martins at the colony site. These agile flyers hunt purple martins in flight. They also lurk around the nests to snatch adults as they come and go to feed young.
Owls
Eastern screech owls and barn owls may pick off an adult purple martin on occasion. But they cause more damage by raiding nests at night and consuming eggs and nestlings.
Crows
American crows sometimes raid martin housing to eat eggs and nestlings. They can perch on the housing and reach into compartments to remove nestlings.
Snakes
Rat snakes and racers frequently climb martin housing to take eggs and nestlings. They will enter nest compartments, swallow eggs whole, and consume nestlings.
Fire ants
Red imported fire ants pose a huge problem, particularly in the southern United States. They invade martin housing and bite nestlings, eventually killing them. They spray formic acid that burns the skin of nestlings.
House sparrows
The non-native house sparrow competes aggressively with purple martins for nesting cavities. House sparrows evict purple martins, destroy their eggs, kill nestlings and prevent martins from successfully nesting.
European starlings
Another non-native cavity nester, European starlings compete with purple martins for housing. They may harass or injure adult martins. Starlings frequently take over martin nests, killing eggs or nestlings.
Raccoons and squirrels
Raccoons and squirrels raid martin housing at night and consume eggs and nestlings. They have very flexible paws and can reach into nest compartments.
Protecting Purple Martins from Predators
The key to protecting purple martins from predators is using properly designed housing placed in ideal locations. There are several techniques martin landlords can use:
Cavity Size
The entrance hole to purple martin nesting cavities should be 2 1/8 inches in diameter. This excludes larger predators, including starlings, owls and hawks, from entering the cavities.
Pole Mounting
Installing martin housing on tall, slick metal poles makes it difficult for predators to access the housing. Poles should be 20-30 feet high to keep the housing out of reach.
Guards
Predator guards can be installed on poles below the martin housing to prevent climbing by snakes, fire ants, raccoons and rats.
House Sparrow Control
To prevent competition and predation from house sparrows, landlords must actively manage nests. This includes checking for house sparrow nests, eggs and chicks regularly and removing them. Plugging cavities and trapping house sparrows also helps.
Colony Site
Locating the martin colony away from trees and wires prevents easy perching for predatory birds. Situating housing over water is ideal, as it deters mammalian predators and fire ants.
Regular Monitoring
Landlords should check houses for competitors and predators at least weekly during nesting season. This allows quick removal of threats.
Deterrents
Using predator guards, removing perches near houses, trimming nearby trees, installing owl boxes and using reflective tape can help deter predation.
Here is a table summarizing some key purple martin predators and techniques to control them:
Predator | Control Techniques |
---|---|
Hawks | Proper cavity size, eliminate perches, deterrents |
Owls | Eliminate perches, owl boxes, deterrents |
Crows | Predator guards, eliminate perches, deterrents |
Snakes | Predator guards, pole mounting, house placement |
Fire ants | Pole mounting, house placement over water |
House sparrows | Entrance hole size, active management, trapping |
Starlings | Entrance hole size, active management |
Raccoons | Predator guards, pole mounting |
Squirrels | Predator guards, pole mounting |
Conclusion
Purple martins face threats of predation from a variety of predators as they nest across North America. Careful placement and management of properly designed martin housing can help reduce losses to predators. Maintaining active colonies will also increase productivity, as martins collectively help defend the colony. With thoughtful housing and diligent monitoring, purple martin landlords can successfully protect their tenants and enjoy their fascinating aerial migrations for many seasons. The rewards of hosting a vibrant purple martin colony are well worth the effort to keep these aerial acrobats safe.