Purple martins are the largest member of the swallow family found in North America. These aerial acrobats have enchanted people for centuries with their skilled flight and cheerful chattering. Purple martins are dependent on humans for nesting sites east of the Rocky Mountains, taking advantage of artificial multifamily housing that became available in the 20th century. But in recent decades, purple martin populations have declined across much of eastern North America. What has caused this decrease?
Where have the martins gone?
Once common in both rural and urban areas of the eastern United States and Canada, purple martins have vanished from many parts of their breeding range. Breeding Bird Survey data show an average decline of 2% per year from 1966 to 2015. The steepest declines have occurred in northeastern states, where martins have largely disappeared from some areas. Martins in the Southeast and central part of their range have fared somewhat better. Nonetheless, the loss of martins has been felt by many people who value these birds.
Why the decline?
The disappearance of purple martins can be traced to several threats that have reduced reproductive success and survivorship:
Loss of nesting sites
Development has eliminated old barns, bridges, and dead trees where martins traditionally nested. In the absence of natural cavities, martins rely on specially designed nest boxes and multi-compartment aluminum housing provided by people. But these human-supplied sites are vulnerable to natural decay, vandalism, or removal when property changes hands. Many martin landlords have not consistently maintained and replaced nesting structures from one generation to the next. The result is that martins in some areas have lost nesting habitat.
Increased competition for nest sites
Two invasive species—European starlings and house sparrows—compete aggressively with martins for nesting cavities. These non-native birds reproduce earlier in spring and may take over martin housing. Landlords who do not actively manage their martin housing to exclude starlings and house sparrows make it harder for martins to nest successfully.
Reduced nesting success
Introduced bird species aren’t the only challenge martins face in raising their young. Bad weather, like cold temperatures or drenching rain, can decimate martin nestlings. Aerial insectivores like martins are vulnerable to periods of inclement weather during the breeding season because fewer flying insects are available to feed nestlings. Adult martins may abandon nests when they cannot adequately provision young.
Decreased survival
Migratory journeys and overwintering in South America expose purple martins to sources of mortality beyond the breeding grounds. Loss and degradation of stopover habitat along migration routes may limit food resources martins depend on to refuel. Deforestation of the Amazon rainforest has reduced overwintering habitat suitability. And martins must navigate thousands of miles despite increasing collisions with vehicles, buildings, communications towers, and wind turbines. Cumulatively, these migration obstacles appear to be taking a toll on martin survivorship.
Why martins matter
More than a sentimental backyard favorite, purple martins fill important ecological roles:
Insect control
Purple martins devour flying insects, including mosquitoes, midges, flies, moths, butterflies, dragonflies, and bees. A typical martin may eat thousands of insects per day while rearing a brood. Colonies of martins provide natural pest control for yards, fields, and wetlands. Fewer martins mean more noxious flying insects.
Seed dispersal
Martins feed heavily on fruits like elderberries, blackberries, and wild cherries during migration. The seeds they ingest and later void or regurgitate help disperse these plants. Declining martins limit this seed dispersal service.
Scavenging
Martins will eat dead insects and small vertebrates encountered during aerial foraging. Although not a major food source, carrion provides martins with nutrients like calcium. Less scavenging by martins may slow nutrient cycling.
Prey base
As aerial insectivores, martins feed other wildlife including raptors, snakes, and mammals that prey on them. Fewer martins limit this food source for predators.
Cavity creation
Martins excavate natural cavities in dead trees where woodpeckers have previously created entrance holes. Over time, martins enlarge these cavities for nesting. Abandoned martin cavities provide future nest sites for other secondary cavity nesters like bluebirds, tree swallows, and owls. With fewer martins, fewer new cavities are created.
Helping martins rebound
Conservationists, researchers, and purple martin enthusiasts are working to reverse the decline of these beloved birds by:
Monitoring populations
Survey programs like the Purple Martin Conservation Association’s Scout-Arrival Study track migration timing and reproductive success to identify population trends. Banding studies help determine where mortality is occurring. Monitoring provides clues to guide recovery efforts.
Managing colonies
Responsible landlords can maximize martin reproductive success by properly siting and installing housing, promptly repairing and cleaning compartments, excluding non-native competitors, and protecting martins from predators, parasites, and bad weather.
Erecting nesting structures
Increasing appropriately sited and managed martin housing expands potential colony sites. Especially helpful are colony houses with ≥12 compartments. Starling-resistant entrances and placement on tall poles with predator guards bolster success.
Supplementing foraging
Some landlords use mealworm feeders to provide a supplemental food source when cold, wet weather limits natural insect prey. This temporary feeding can help martins survive brief storms.
Enhancing stopover habitat
Planting native berries and maintaining wetlands along migration routes gives martins the food and shelter needed to rest and refuel during travel. Protecting stopover areas enables more martins to successfully complete journeys.
Educating others
Outreach programs explain martins’ needs, showcase model colonies, train new landlords, and inspire young naturalists. Getting more people engaged in martin conservation increases participation in monitoring, housing, and habitat improvement projects.
Studying threats
Ongoing research examines hazards to martins, from pesticide exposure to building collisions. Understanding threats better informs efforts to reduce mortality and safeguard martin populations.
Reasons for hope
Despite ongoing challenges, there are promising signs suggesting purple martins can recover:
Breeding in cities
Some metropolitan areas with committed martin landlords maintain thriving colonies. Urban martins prove these aerialists can still flourish when provided suitable nesting sites and foraging habitat.
Expanded wintering range
A small but growing number of martins that forego migration are staying year-round in south Florida and the Gulf Coast. These nascent non-migratory populations indicate martins have some flexibility to adjust ranges.
New technology benefiting management
From online migration maps to trail cameras monitoring nests, new tools aid martin conservation. Emerging technology holds potential to improve housing, reduce threats, and unlock insights to help martins.
Increased passion among devotees
Thanks to the mentorship of experienced martin landlords, more people are actively managing colonies. This expanding pool of knowledgeable and dedicated martin stewards boosts hope for the future.
Ongoing protection of South American habitats
Conservationists are working to safeguard wintering grounds in Brazil, like the Cerrado grasslands, that are vital to martins. Maintaining these ecosystems augments overwinter survival.
Creative problem solving
Innovative strategies like supplemental feeding, artificial roosts, and martin nest cams demonstrate out-of-the-box thinking to give martins an edge. Continued creativity and openness to new approaches will be key.
The future of martins
Purple martins still face grave threats, but their resilience shows recovery is possible with expanded human commitment. More widespread monitoring and management, improved policies and legislation, advanced research, and enhanced education programs offer promise if implemented diligently. By working together, people passionate about martins can bring back these birds to brighten our skies once again. The fate of the purple martin remains uncertain, but one thing is clear: people power gives martins the best chance to thrive again.
Conclusion
In summary, purple martin populations have declined due to loss of natural nesting sites, competition from invasive bird species, reduced nesting success, and lower survivorship along migration routes and in wintering grounds. But martins provide valuable ecological services and appeal to people, so conservationists are working to help them rebound through monitoring, habitat management, supplemental feeding, education programs, and research. Martins face ongoing threats, but successful urban colonies, new technology, expanding ranges, and increasing stewardship efforts give hope martins can recover with vigorous human assistance. The outlook remains challenging, but people power makes a positive difference for martins. By joining forces to implement creative solutions, martin devotees can bring back these popular aerialists to again fill our skies with their grace, charm, and enthusiasm for living.