One of the most sought-after birds that homeowners wish to attract to their yards is a colony of purple martins. The largest of the swallow family, martins have adapted well to living in close proximity to humans. Through our fascination with these birds, they have, over a period of time, developed a partnership of coexistence with humans. But this partnership did not develop overnight, or even in recent decades. It took over a thousand years for purple martins to gradually develop a sense of trust in their new landlords.
At one time the nesting habits of purple martins was dramatically different than today. These birds nested in abandoned woodpecker chambers, rotted-out cavities in stands of dead trees or naturally occurring holes in cliffs and steep banks. In modern times, however, martins have adapted to nesting in housing provided by humans from multi-room boxes know as “martin houses” to hanging natural or artificial gourds.
How did the ancestral nesting habits of purple martins change? It may have been by sheer accident. Perhaps the earliest Native Americans found martins nesting in a hollowed-out gourd that was used as a utensil and soon discovered martins could be attracted to nest in gourds that were hung with holes in them throughout their campsites. We can only speculate how this transition began, but over hundreds if not thousands of years, we know that purple martins gradually gave up their ancestral ways in a process referred to as a “behavioral tradition shift.”
When martins began nesting near humans, they encountered fewer predators. The gourds provided martins a larger chamber than the natural cavities that were available so they were able to lay more eggs and successfully rear more young. It would have been adaptive for those young martins that fledged these nesting structures to seek out gourds the following year as breeding adult birds. At the same time Indians may have discovered the benefits of purple martins nesting in close proximity to their encampments. Documents from the 18th and 19th century indicate nesting martins attracted to these early American villages became excited and warned of approaching strangers, drove crows and blackbirds away from patches of corn and drove vultures away from meats and hides hung out to cure. This mutual benefit that developed over time between purple martins and humans exists to this day.
Purple martins may also have acted as a seasonal calendar for Native Americans with their cyclic arrival, nest building, egg laying, fledging of young and departure. They may have assisted in arousing the camp in the early morning with their singing. And much like today, the martin’s pleasant song and aerial behavior is a source of wonder and entertainment. There is also some evidence these earliest Americans may have used dead purple martins as a natural repellent to protect their furs from insects during summer storage.
It may have been for some or all of these reasons that other native tribes began the cultural tradition of hanging gourds to attract purple martins, and eventually over time martins began to select gourds as nesting sites over natural cavities. As the Europeans entered the New World, they adopted the custom from Native Americans of hanging gourds to attract purple martins. These colonists soon introduced ceramic gourds and eventually wooden houses. From there it wasn’t long before the eastern population of purple martins began nesting exclusively in housing provided by humans, and the behavioral shift was complete.
Today there are no purple martins east of the Rocky Mountains observed nesting in natural cavities. They have become the only bird entirely dependent on humans to provide nesting structures. Martins have been managed by humans longer than any other North American bird species. There is some concern that if humans were to stop supplying nesting structures for these birds, they may likely disappear as a breeding bird in eastern North America.
With the introduction of two cavity-nesting species, the English (house) sparrow and European starling in the mid-1800s, purple martins faced a new threat. These non-native birds aggressively competed for nesting structures provided by humans, often driving off colonies of martins, even killing some. To this day house sparrows and starlings are the number one threat to nesting martins in poorly managed purple martin houses. Loss of habitat and these two invasive bird species have reduced the purple martin population to 10 percent of that in the 1800s. But the odds are favorable that if you erect a martin house, following some simple guidelines and management practices, you’ll attract a nesting colony.
Adult male purple martins are a shiny dark purple with blackish wings and tail. Females and subadults have a gray chest with whitish belly. The back is a dull purple with black wings and tail. They are typically 8 inches long and have a wingspan of 12 inches. Except for a few areas of the Rocky Mountains, they are found throughout most of North America. Purple martins winter in Brazil, returning to the United States in early spring using three different flyways. The Baja Peninsula is used by martins that breed west of the Rockies. The Louisianna flyway is used by martins that traverse the open waters of the Gulf of Mexico and nest throughout the central part of the U.S. The third flyway is through the Florida Keys for martins that populate the east coast into Canada.
The average arrival date in the U.S for martins migrating from South America is mid-February in southern states and March through May in northern states and Canada. Purple martins will gather in large premigratory groups numbering in the thousands beginning in August before heading back to the Tropics in September to spend the winter months.
Purple martins arrive in the Central Great Plains by late March but may retreat back south for a short time if the weather goes bad. They do not begin nesting right away but may spend several days feeding to replenish their energy from the long flight. The first to arrive are adult males, often referred to as scouts. Most of these birds already have established colonies and are returning to housing used in previous years. The female martins and subadults, birds hatched the year before, follow a week or two later. The females will return to the colonies where they had prior nesting experience. The subadults remain restless for a period. But these are the martins credited for locating newly erected or abandoned martin houses well into April and early May, where they will form new colonies after they have settled down.
Purple martins form a monogamous pair bond with both sexes sharing the nest construction using leaves, pine needles, grass and twigs held together by a mixture of mud. The female lays two to seven pure white eggs at a rate of one egg per day. She will incubate the clutch for approximately 15 days. Once the eggs hatch, both parents will feed the nestlings continuously for a period of 26–32 days until the young birds are able to fledge from the house. The parents will continue to feed and care for their offspring for a few more weeks. During this time it is not uncommon for these fledglings to return to the safety of the house for the night.
The purple martin feeds exclusively on flying insects such as beetles and dragon flies. They are beneficial to humans because their
diet includes many destructive insects. While it is widely believed they consume large quantities of mosquitos, extensive research has failed to justify that claim. Mosquitos remain close to the ground and are most prolific at night when martins are roosting. It is also more efficient for birds to collect a few large insects as opposed to the time and energy it would take to collect several thousand mosquitos. When feeding, they can reach speeds of 45 miles per hour and have been clocked at 60 miles per hour with the wind behind them. It is a joy to watch their aerial manuvers as they feed or at times when they soar for the apparent fun of it.
So what does it take to become a purple martin landlord? After all, this is a relationship that developed between martins and humans over a very long and historical period. When a homeowner installs a purple martin house, they assume a certain responsibility to manage that piece of real estate in the sky. But the benefits of attracting purple martins are no different today than what the earliest Americans enjoyed.
A prospective purple martin landlord must first consider if they have the habitat to attract martins: Open space. The martin house must be located a minimum of 40 feet from any tall trees or structures, the more room the better, and have no overhanging branches above the house. Orientating the doors of a purple martin house so they face toward wide-open corridors may be sufficient, but you still need to maintain open space above the house and prevent trees from encroaching on the sides. Many properties in urbanized areas provide good martin habitat as do rural areas, but heavily wooded neighborhoods do not. Anyone who currently has a purple martin house that does not meet these minimal requirements should remove it immediately as they will not attract martins and the house will become a breeding ground for house sparrows and starlings, birds that have had an enormous negative impact on many of North America’s cavity-nesting birds including bluebirds and woodpeckers.
Along with adequate space a martin house should be located within 150 feet of an occupied dwelling. Martins have made an association, as they did with Native Americans, that nesting in close proximity to human activity reduces the risk of predators in the area. It is also recommended not to landscape around the base of the pole with shrubs as this provides a place where predators may lurk.
A good purple martin landlord is one that will manage the house, lowering the nest box weekly to evict unwanted bird species and make certain all is going well. This human interaction will not deter nesting martins but actually enhance the martin’s ability to have a successful nesting season and fledge their young without problems. If you are unwilling to be a good property manager, you may want to reconsider becoming a purple martin landlord.
When investing in a martin house, make certain it is durable enough to withstand years of use. Many purple martin landlords have had boxes occupied for 20 years or more. Select a system that can be raised and lowered with little effort. Aluminum houses seem to be best suited for the purple martin. They are lightweight, making them easier to maintain, do not harbor parasites, are easy to clean, and are cooler if properly ventilated. A roof made of reflective material is preferable because of the heat factor. The ideal height is 10 to 14 feet, but it can be much higher if desired. And make certain before purchasing a martin house that it can be located in an area at least 40 feet from tall objects such as trees or buildings.
If you determine you have the proper habitat to attract purple martins and are willing to commit to being a faithful manager of the colony, you will certainly be rewarded by the martins that take up residency. They will return year after year. Many successful landlords speak about their purple martins as if they are extended family members and anxiously await their return each spring. But martins are very sensitive about the housing that is offered to them. There are a number of reasons why one may fail to attract nesting martins, or lose them once they have established a colony.
Here are a few common reasons why one with good intentions may fail to attract a colony of purple martins:
- The house is located to close to trees or in a yard that is too enclosed with mature trees and tall structures. This cannot be overemphasized.
- Other bird species were allowed to claim the martin house first, and once they have completed constructing a nest, will ward off any martins that show an interest.
- The martin house is erected too far away from human dwellings.
- The house is not painted white. White helps martins detect the dark openings of cavities better, reflect heat, making the house cooler, and may even enhance the male’s courtship display as he attempts to attract willing females.
- Failing to open the doors of a martin house in time or closing the doors too early means you may miss your opportunity to have a colony. Remember that it is the subadults that start new colonies, often during the last three weeks in April to early May.
- Vines and shrubs are allowed to grow under the housing where predators could lurk.
- Prospective landlords buy or build housing that cannot be easily managed. This leads to a host of problems.
But even once a colony of purple martins have taken up residency in the house you made available to them, and even if everything appears to be satisfactory, there are a number of reasons why a martin colony may unexpectedly abandon the house:
- Predation at the nest can cause abandonment. The most common predators are squirrels, raccoons and owls. Occasionally snakes may pose a problem. Even the presence of predators constantly lurking near the martin house may cause abandonment by the colony.
- The encroachment of trees.
- Weather extremes. A martin’s diet consists solely of insects. Extended periods of cold damp weather or extremely hot conditions deplete the availability of insects. Heat and humidity in poorly ventilated housing can also lead to fatalities in the colony.
- The house becomes overrun with nest site competitors, primarily house sparrows and starlings.
- Parasite infestation. The remedies for this problem are simple if there is early detection of the problem from regular inspections of the martin house.
- Not enough housing for a growing colony. Purple martins will only use approximately 60 percent of the available rooms in a martin house. With no room for expansion, the colony could be lost through attrition as the returning adults grow older and die off.
- The widespread use of pesticides. It is rare that martins come in direct contact with pesticides, but it can reduce a martin’s food supply. Adults may feed on contaminated insects and pass this contaminated food source to their young.
- Failing to open the doors on time for a returning colony of martins.
- Failure to maintain the original orientation of the doors after inspecting the house. This may cause an adult to inadvertently enter another martin’s nest.
- An existing martin house was replaced with a martin house of a new design between seasons. The returning colony may not identify the new design and move on.
Purple martins have fascinated human beings from the time of the Paleo-Indians in A.D. 900, who may have started the behavioral transition of martins, to modern day purple martin landlords. This may have been an extreme adaptation of a bird species that moved from its natural habitat to gourds and finally to precision-tooled housing in an attempt to adapt to human activity. While I encourage those with the proper habitat to consider becoming a purple martin landlord, I also ask those with a martin house in habitat avoided by martins that has become a breeding spot for invasive species to relocate the house or remove it completely. Either of these steps would significantly help in the conservation of purple martins, a unique bird species that has accepted man as a close friend and neighbor.