The Big Three...Other Factors That May Prevent Purple Martins From Colonizing New Sites

From: Steve Kroenke, Tallahassee, Florida
Date: 2/11/01
Time: 7:45:55 PM


The Big Three - Other Factors That May Prevent Purple Martins From Colonizing New Sites

You have done everything the experts have told you to do. I mean everything. Your colony site is wide open and could accommodate a 747 jet; you have erected the best designed houses/gourds; you "flame" every starling/sparrow that flies over; you build artificial nests and smear mud on the entrance holes; you play the dawn song; you attach decoys; and you even pray. But all to no avail. No matter what you do, you still canít permanently attract martins to your seemingly ideal site. Subadult (SY) males may show up and even establish temporary territory. But any females they attract just shun them and move on. You shake your head in frustration. You sit back and again take one more look at all your fancy houses/gourds in a great, open site and you only see martin paradiseÖbut there may be complications in paradise. There may be something else at work here and you probably have no control over it. What could be so wrong when you have done everything so right?

It Happens To The Best Of Us

Some folks across the country, but particularly in the northern tier of states, often experience trouble in attracting martins. These folks try and try and try each season and not a single martin nests. This may continue for years. These are cases where the potential landlord has done everything he/she can to attract martins and seems to have a good colony site. It is usually not sparrows, starlings, predators, trees, inappropriate housing/gourd designs, or poor colony management practices that are preventing colony establishment. It may be something elseÖ

So what may be going on in those cases where a person appears to have the ideal setup but the martins just will not stay? Again, what could be so wrong when you have done everything so right?

The Big Three May Be At Work

Okay, we know about the obvious causes for preventing martin colonization at your new site: predation, interspecific competition with sparrows and starling, unsuitable habitat (too many trees), inaccurate house design, and improper colony management practices. But these donít appear to be issues. No one knows for sure why martins accept or reject one site over another when both sites appear perfectly suitable. However, I do believe we can identify some "other" factors that may be at work here and then offer suggestions to possibly explain this paradoxical phenomenon. It appears to me that three main factors could be involved in those cases where potential landlords have done everything apparently correct, but still canít attract martins. Though I believe these factors are all interrelated, some may exert a stronger influence. So what are these three mysterious factors that could be preventing martin colonization of your apparently perfect site? Here they areÖ


There is a basic universal law that seems to strongly influence many biological, social, and economic systems. It is simply numbers; nothing really complicated here. You do the math and the numbers just donít add up. If you are marketing a great product, but you have a small customer base, then you probably will not sell much. If purple martin numbers are declining or low in a particular area, then the chances of attracting martins naturally decrease. Simple numbers game. You and many other potential landlords can erect the best houses/gourds in the best locations and follow the best colony management practices, but still canít attract martins because there are so few martins seeking territory in your area. It is martin population dynamics.

Higher Martin Numbers In The South And Lower Numbers In North

The Breeding Bird Survey and Purple Martin Conservation Association (PMCA) have documented over the years that purple martin populations generally may be declining in many northern states and either remaining stable or increasing in portions of the south. Why? No one knows for sure of the reasons behind these population trends, but there are some likely candidates. Adverse weather conditions have negatively impacted martin populations in the northern tier of states on occasions, sometimes decimating huge numbers of adults and their young. These climatic disasters seriously deplete the local purple martin population in the short run thereby making it more difficult to build up the numbers. Interspecific competition with house sparrows and starlings has seriously harmed purple martin populations throughout the United States and in Canada. Poor colony management practices and inappropriate housing designs have exerted an insidious effect for a long time and continue to do so. And just a lack of interest by the public in erecting martin houses/gourds has possibly contributed over the long-term to the decline of purple martins in certain regions of the country. The south has managed to sustain its higher purple martin numbers probably because of the large established population that has existed for many years and favorable weather conditions.

Maybe History Has Something To Do With It

We know the southís more suitable weather factors enhance martin living conditions. But there may be more to it than just temperatures. The south has the martin numbers on its side and maybe history has something to do with it. People may have been erecting houses/gourds in the south for a longer time than in many areas of the north. It is believed that southern Native American tribes started the tradition of hanging hollow gourds for martins and they had been doing this for possibly hundreds of years before arrival of the European settlers. This may have given the edge to southern martin populations to grow at a faster rate and build a larger established base for a longer period of time. If the martin population is large to begin with in a particular area, then naturally more young are raised. The population cycle continues and sustains the growing numbers over many generations of martins. And could these generations of martins have something "deep inside them" that keeps them in the south or north?

Could It Be In The Genes?

There could be an intrinsic factor that is deeply embedded in the purple martin genetic code (DNA) that influences martin nesting migratory patterns and possibly impacts population levels across the country. Could there be "local gene pools" inherent in martin populations that have developed for thousands of years and tend to remain genetically "attached" to specific regions? For example, do martin populations that have bred in Louisiana and surrounding states for thousands of years continue to breed in that general area based on some hidden signal stored in their DNA? Perhaps martins that have nested for thousands of years in the south or north have been genetically programmed to continue this tradition and return, in part, to an area based on such intrinsic factors. Would a martin that was born in Minnesota decide the stay in Mississippi when migrating from Brazil during the spring rather than continue flying north? Or would a martin born in Florida skip Florida and move further north to Pennsylvania for the next breeding season? No one knows if and how genetics may influence purple martin population levels based on geographical location, but research into DNA differences among martins across various states could possibly shed some light on this intriguing subject. And for all we know, it may have nothing to do with genetics and could be just "geographical imprinting". That is, young martins imprint on the location where they were born and then return to the same general area the following year. There is still so much to learn about martin biology and behavior.

Population Pockets Of Abundance May Exist

However, even in high martin population states like Louisiana and Arkansas, you may see pockets of low martin abundance. And conversely, you may have pockets of high martin abundance in generally low population states like Michigan and Nebraska. These population pockets may be influenced by topographical factors such as forests, water availability and mountain ranges. Also, a pocket of high abundance in a state that is generally low in population may reflect historical precedence of people erecting houses/gourds for many generations in that area and properly maintaining the colonies.

So One Of The Big Three Is Operational

Okay, the first factor of the big three seems to be in play. You may live in an area of low purple martin population or an area where martins are declining. So not as many martins are seeking territory in your particular location. It is simply numbers at this point.

Now, what about the second factor? Well, there is an intrinsic factor that could be hampering your chances of attracting martins. This is something "inside" a martinís genes and is expressed by behavior and there is nothing you can do about it. This factor is very powerful, particularly in areas where martins are uncommon.


Purple martins are swallows and, like most swallows, they typically prefer to be together. So martins tend to seek out colony sites that already have martins in residence or sites that may be unestablished, but are located very close to active colonies. Martins usually follow other martins. Established colonies may indicate to a martin that there are available nest sites, mates, and that the chances of reproductive success are good. That is, the site may have a "proven track record". Why take a chance at breeding at an unestablished site when the odds of being successful may be better at a colony with permanent martin residents?

The Males Are The Risk Takers; The Females Are More Choosy

Male martins setup territory at either an established or unestablished site, defend it against other males, and then compete for available females. The males are the risk takers and seem to be more willing to choose a variety of territories even those that may or may not be that suitable to any females they attract. When nest sites are uncommon and both inter (between different species) and intraspecific (between same species) competition is intense, male martins canít afford to be that choosy.

But females can be highly selective and they certainly are. The female martins do not establish territory so they are not under the substantial pressure that males must face. Females can be highly selective and take their time as they respond to the mate attraction displays of various males. For the females, it is in their best biological interests to return to the general colony area where they nested previously and review several males before making a selection. She is naturally seeking the "best male and best territory" for her nest. All the pressure is on the males, not the females, in territory establishment.

SY Males Are Usually The Pioneers Of New Territory

Male martins, particular SY males, may seek new territory away from established colonies based on intraspecific competition with more dominant ASY males. Even though there may be sufficient nesting sites at an established colony to accommodate these SY males, these males may be unable to secure territory because many ASY males dominate multiple house compartments/gourds. It is these SY males that are often the "pioneers" of the martin species and established new colony sites. However, ASY males, that may have lost their previous colony site or were unsuccessful in nesting the previous season, will also "pioneer" new territory just like the SY males.

Male And Female Martin Social Behavior Impacts Colonization Of New Sites

As mentioned before, the male martin has to be a risk taker in both finding, establishing and defending his territory. He canít be that selective when he is competing not only with other territory hungry male martins but also with ferocious competitors like house sparrows and starlings. Both SY and ASY males will seek out new colony sites if necessary and then try to attract females.

Though the male martin establishes the territory, this territory does him little good if he cannot successfully attract a mate. The female martin seems to ultimately do the choosing and the male does not force the female to accept him and his territory. He must attract her through his vocalizations and behavioral displays, his "fitness", and the suitability of his territory. She may "review" the territories and "fitness" of multiple males before deciding. She can afford to be highly selective and take her time; she does not appear to be a "risk taker". At unestablished sites where one or just a few males, particularly SY males, are defending territory for the first time, then females may decide against these males in favor of ASY males at more populated established colonies. Females may be seeking out the "best", more "experienced" males as their mates. This can be very frustrating to not only the mate hunting SY male martins but to the anxious martin landlord who is trying to attract martins for the first time. Martins seem to prefer nesting at established colonies that already have a population of martins in residence; this seems particularly true for females. From a biological perspective, it "makes sense" for female martins to gravitate toward established colonies as this may be an indication to the females that the chances for successful nesting would be greater. Also, the females would have a greater selection of males to "review" and therefore a better opportunity to select an "experienced" ASY male as a mate. Her genetic legacy is her young and she would "want" the "best" and most "experienced" male to father her babies.

The Bottom LineÖThe Females Are Selective And Seem To Prefer Males At Established Colony Sites

So the bottom line is that male and female martins seem to prefer nesting at established sites. Females are even more prone to seek out established sites where they have a better opportunity to select an experienced ASY male or even an inexperienced SY male, as both would have "proven" territory. Female martins may view established colonies as "proven" in their reproductive successes, so she would naturally select males at such sites. She would want the best male and best territory for her nest. Why take a chance on an immature SY male at an unestablished site with no "proven track record"? Martins only live on average four or five years, so time is critical in the breeding game.

You May Have Two Of The Big Three

So you now have two possible factors operating that may be reducing your chances of martin colonization at your site: low martin population in your area and the preference of martins to nest with each other. These factors are out of your control and there is not much you can do. However, there is another factor that can significantly hamper your efforts to attract martins and it is human made. This factor is just an extension of the previous two, but primarily works against you because of a martinís propensity to nest with other martins. This factor may ONLY be an issue in areas of low martin numbers or where martins are significantly declining. It is usually not a problem at all in high martin population regions.


We all know that the earth and other planets revolve around the sun. The sun is the cosmic magnet that keeps the planets on course and sustains life on earth. Well, there is a human made "sun" that exerts a similar effect on purple martins and functions as a biological magnet and sponge, attracting and soaking up most of the martins in the immediate area. It is ground zero for any martins that are in the immediate area and pulls them in from all directions.

And guess what may be soaking up all the martins a few miles down the road from your unestablished colony siteÖ

As discussed earlier, martins are attracted to sites with other martins in residence and nothing is more attractive to martins than a super purple martin colony (SPMC) or other large established colony. SPMCs work hand in hand with the martinís affinity for nesting with each other. This is typically a colony of 70 or more martin pairs (but could be less) nesting in a group of houses or gourd clusters. There are huge numbers of martins calling and socializing, multiple cavities, and for females, good chances to select an experienced ASY male as a mate. Multiple cavities are highly attractive to martins and give both male and female martins a choice in both territory and potential nest sites. A SPMC may indicate to other martins, particularly females, that this site has a "proven track record of reproductive success". Additionally, females would have a greater opportunity to mate with an experienced ASY male. Her genetic legacy is her young and she is looking to mate with the best male with the best territory. As mentioned before, why would she take a "chance" on a SY male at an unproven, unestablished site? And many SY males, which typically colonize new sites, will try and try at these huge colonies to establish territory because of the abundance of nest cavities and a greater availability of females looking for mates. A SPMC seems to be an irresistible force that draws in both ASY and SY martins as they seek nesting sites and mates. This seems to be particularly true in areas of low martin abundance or where martins are declining. What few martins are in the area are naturally attracted to the main source of martin activity with the most available nest sites and possible mates and that is often the local SPMC.

SPMCs May Prevent Colonization Of New Sites In Areas Where Martins Are Uncommon

So SPMCs or other large established colonies in an area of low martin population may attract nearly all the available ASY and SY martins that may be seeking nesting sites. Martin social behavior exerts an extraordinarily strong force and pulls martins toward established colonies. Again a martinís affinity for nesting with other martins, and particularly the female martinís attraction to established colonies greatly enhances the "biological sponge" effect of SPMCs. SPMCs may be unintentionally preventing the martin colonization of new sites in areas where martins are uncommon.

Okay, You May Have One Or All Three Factors Working Against You - But There Are Still Possibilities

It seems like a mission impossible at times, particularly when you have tried for many years to attract martins. You have the big three working against you. However, this is not necessarily a permanent situation and things do change. Older martin colonies, including SPMCs, rise and fall and with these declines the surviving or remaining martins seek out new sites. Martins are highly mobile and nomadic. They can fly many, many miles in search of nesting sites and the SY birds often nest AWAY from their natal colonies. It is biologically adaptive for them to do this to reduce inbreeding and "cast their genes out into the system". There is always the possibility that SY males, and most important females, will eventually colonize your site in spite of the "big three". And there is something else you can do that may give you more insight into your chances of attracting martins in your particular area.

Visit The Local SPMC Or Other Established Colonies In Your Area

You know you canít alter purple martin population dynamics in your area. You canít change martin social behavior and force a female martin to accept SY males that may set up territory at your site. But you can stop by the local SPMC or other established colony and talk with the landlord. Most purple martin landlords are more than happy to discuss their colonies with other folks. Find out how many compartments/gourds the landlord has erected. Try to determine the number of nesting pairs and the approximate ratio of ASY to SY birds. How long did it take the landlord to attract martins? Martins increasing or decreasing? Sparrow/starling problems? Predator problems? Good colony management practices? Is he/she planning to continue adding more houses/gourds? Does he/she take care of the colony? And possibly the most sensitive question of all: would he/she be willing to either not add any new houses/gourds or maybe even reduce the numbers already available? Answers to these questions can give you valuable insights into your current situation and may indicate your chances for eventual colonization at your unestablished site.

If the landlord does not practice good colony management, then his/her colony may be declining and the martins may seek other nest sites. Intense competition with sparrows and starlings may force the martins to leave or frequent predator attacks may drive the martins away. If the site is tree encroached, then the martins may abandon the site in time. This would be a chance for you to perhaps attract these martins if you keep your colony site in good condition.

Is he/she planning to add more houses/gourds for the upcoming season? If yes, then this could be a negative for you. If martins are uncommon in the first place and may be declining, then the SPMC with added nest sites will just continue to soak up most of the birds in your immediate area. Remember: martins, particularly the females, prefer to nest with other martins and a SPMC with its concentration of martins and multiple nest sites is a biological magnet for all martins in the area.

The Big Three Are Powerful - But Donít Give Up

So purple martin numbers, behavior, and SPMCs may work together or alone to prevent colonization of new sites in areas where martins are uncommon or are undergoing significant declines. The big three sound ominous and may seem insurmountable at times. But things change. Martin population levels are dynamic and you never know from year to year what could happen. It is critical that potential martin landlords continue to try to attract martins, particularly in areas where martins are scarce or undergoing population declines. Donít give up.

Steve Kroenke, Tallahassee, Florida

Back to Archives