Reprinted from: Purple Martin Update 4(1): 26-29
James R. Hill, III
Purple Martin Conservation Association
According to a detailed questionnaire the PMCA sent out during the 1989 breeding season, fewer than 20% of North American martin landlords conduct regular nest checks on their martins during the breeding season! This means that more than 80% of the people trying to help martins are doing so in a less than effective way. It also may explain why the martin population is declining in so many areas, and only inching up continent-wide, rather than soaring up, as it could be. Interestingly, the same questionnaire showed that the average number of martin pairs attracted to sites where regular nest checking was practiced was 22 breeding pairs, compared to only 10 pairs at sites where no regular checking occurred. (The actual difference is probably greater than this, since landlords who don't do regular nest checks, invariable overestimate their colony size and nesting success. They typically report having a 100% hatching rate, a 100% fledging rate, and a 100% occupancy rate, since they never find any unhatched eggs, dead nestlings, or empty compartments when they clean their houses out at season's end. Obviously, had these folks done regular nest checks, they certainly would have discovered eggs and nestlings that had disappeared prematurely, and several nests that were never used. This is the norm.) Although it's hard to prove that this impressive doubling of colony size is due strictly to better landlord management, it certainly is highly suggestive.
Why are so many martin landlords reluctant and/or afraid to lower their martin houses during the breeding season to conduct weekly nests checks? I think it's because, as children, we were told by our parents that touching or disturbing a bird's nest would cause the parents to abandon their young. We now know that such assertions are false and amount to nothing more than 'old wive's tales.' Birds will not abandon their nests or young when touched by humans - they have far too much "parental investment" accumulated in them by that stage to be so wasteful of their reproductive effort. In fact, anyone who has tried to discourage English House Sparrows or European Starlings from nesting in their martin houses by repeatedly tearing out their nests, knows how nearly impossible it can be to cause a bird to abandon its breeding site. It's the same with Purple Martins - humans can lower their housing, handle their nestlings, and even replace their wet nests, as often as they like. None of these activities will cause martins to abandon their nests, young, or colony sites. Martins are incredibly tolerant of human disturbance, which is good, because conducting weekly nests checks is unquestionably the most beneficial activity a landlord can do to help their martins. Leaving them undisturbed, on the other hand, can, and usually does, lead to lower reproductive success. Ironically, you are far more likely to have your martins abandon your site by not doing nest checks than by doing them. If you want to do what is best for the martins under your care, get out there and do weekly nest checks!
Unfortunately, many of the people who get into the martin hobby don't understand or realize the effort and commitment that correctly hosting martins entails. Having a successful, growing martin colony is similar to having a garden - there's a lot more to it than just poking some vegetable seeds in the ground then ignoring the site until harvest time. Conscientious gardeners would never dream of not checking their gardens for an entire summer. They know that gardens require weeding, watering, fertilizing, cultivating, pruning, fencing, staking, insect control, and record keeping. Likewise, there's more to having a successful martin colony than just sticking a house on a pole. Just as certainly as weeds and insects will invade a garden, unwanted pests will compete with your efforts to raise martins. Conscientious martin landlords would never dream of not looking inside their martin houses weekly. Without knowing exactly what is going on in each nest, a landlord would have no clue if owls, raccoons, opossums, squirrels, or pole-climbing snakes, were secretly eating their adults, babies, and eggs, or if the nests had become loaded with blowflies, fleas, or nest mites, or if the nests had become dangerously rain soaked, or if a nestling or parent had died in the compartment requiring removal, or if paper wasps had moved in, or if Starlings or House Sparrows had invaded. And without accurate records, a landlord would have no idea where to replace nestlings that had wandered into neighboring compartments, or prematurely fallen to the ground. A landlord would also not know in which compartments young had inexplicably disappeared before they were old enough to fledge. Not finding and reacting quickly to most of these problems can greatly reduce the breeding success of your martins, or worse, cause complete (and often permanent) colony loss.
Being a Purple Martin landlord and not conducting weekly nest checks is like driving a car with your eyes closed. Only by doing weekly nest checks, can a landlord receive the feedback necessary to react in a timely fashion to the multitude of problems that face the martins depending on their care. To be the host of a growing martin colony, requires parasite control, nest-competitor control, wet nest replacement, anti-predator devices, eggshell and nest material supplementation, premature fledgling replacement, dead bird removal, compartment numbering, daily walk-unders, weekly nest checks, record keeping, and the regular pruning of nearby bushes and trees. Without this constant attention and level of commitment, neither a garden, nor a martin colony, will have much to show for itself at season end.
Here at the PMCA, we typically get daily letters and phone calls all summer from distraught landlords wanting to know why their martins had "abandoned" their colony site or migrated early. Inevitably, we discover none of the callers had been doing weekly nest checks, and consequently, had no idea if their young had fledged successfully. Had these landlords been doing regular nest monitoring, they would have known if there really was a problem at their sites. Only by doing weekly nest checks can a landlord actually know what is going on at their site, the timing of each phase in the nesting cycle, and how many active nests (i.e., nests with eggs or young) they have, and thus, the number of breeding pairs.
So, why do so many martin landlords elect not to conduct weekly checks? First, many have housing that doesn't allow for easy, vertical lowering - they have housing on rigid poles, or poles that only tilt down. Others have compartments without doors that open easily. And finally, many have the mistaken impression that lowering their houses during the nesting season is somehow detrimental to the martins and will scare them away. As stated above, nothing could be farther from the truth! You can lower the housing daily, if you like, and touch the young and eggs all you want. There is no risk that any of these actions will cause nest failure or colony-site abandonment. Martins are remarkably tolerant of house and gourd lowerings. In fact, I'm convinced that landlords who conduct weekly nest checks raise significantly more nestlings per nest than landlords who don't.
Uninvolved martin landlords (no matter how well-intentioned they may be), aren't helping Purple Martins as much as they could be, or as much as they might think they are. Landlords need housing that can easily be lowered, and compartments that open quickly for weekly monitoring. Housing on stationary poles, or poles that only tilt down, don't meet these requirements and should gradually be replaced. A landlord with housing that doesn't winch or telescope up and down, will find it much harder, or nearly impossible, to effectively help the martins in their care.
How to Monitor Your Martin Nests
The most important thing to do before each nest check, is search the ground underneath the housing for dropped items. Actually, you should do these walk-unders daily. You may find dropped prey, dropped nest material, thrown out eggs or eggshell hemispheres, dead nestlings, starved adults, plucked martin feathers, or shed owl feathers. All these dropped items are clues to what is happening above.
After a thorough walk-under, lower your martin house, vertically, if you have a winch-operated or telescoping martin pole. Once lowered, some house models still may require the use of a short step ladder to reach the uppermost compartments. If you have poles that only tilt down, DO NOT lower the housing - the tilting will smash your martins' eggs, nests, and young. People with tilting or stationary poles can only do nests checks from the top of an extension ladder leaned against the house. However, this is extremely dangerous and is not recommended, especially with fragile metal houses on thin steel poles.
|The author checking the nests in a home-made, winch-operated, martin house. The doors open on hinges, and lock with hook and eyes.|
Once your house is lowered, quickly begin by opening the door to compartment #1. If there is a completed nest in it, but no eggs visible, gently dig for buried eggs under the leaves with your finger tips. Record the contents onto the nest record card for that compartment, then close the door securely and move on to the next compartment. Once every compartment has been carefully inspected and the data recorded, raise the housing to the height it was previously, and walk away, so the parents can return to incubate eggs, feed their young, etc. If you have telescoping poles, it is imperative that you mark each joint with alignment marks (use paint or a water-proof Magic Markers) to insure that the house gets reoriented to the exact compass direction between nest checks. Martins only recognize their own nest by its height and compass direction. Misorientation of an active martin house can cause the martins to throw out "foreign" eggs, kill "trespassing" nestlings, and even kill each other in squabbles over compartment ownership. A single house orientation mistake is disastrous for the reproductive success of a martin colony, a mistake that can cause total colony-site abandonment.
|It is imperative that martin landlords with telescoping poles, mark alignment tabs at each joint, especially if they conduct weekly nest checks. This insures proper reorientation of the housing after each lowering. A misorientation error will wreak havoc with your martins and can cause colony-site abandonment. The vertical lines are the alignment tabs. The horizontal line is 15 inches from the bottom of the inner pipe, and insures that the pole isn't dangerously overextended.|
Checking gourd nests is a bit different. You will need a flashlight to illuminate the contents and a long, thin twig to gently push the leaves off the buried eggs for an accurate count. The eggs will always be in the center of the leaf-lined nest bowl, in the lowest depression. Be very gentle or you could smash them.
|The author checking the nests in a lowered gourd rack. Typically, a penlight is used to illuminate the contents of the gourd, and a twig to gently lift any green leaves that may be hiding the martin eggs.|
What Information to Record
Here at the PMCA's research grounds, during each nest check, we record the contents of every gourd and each nesting compartment. The nest record card shown in Fig. 1 demonstrates the kind of information that is important to record. As you can see, we write down whether there is nothing in the compartment, or a trace amount of nesting material, or a partial nest, or a nest with green leaves. Later in the season, we record the number of eggs. Great care and diligence must be used when trying to count martin eggs since the birds often hide them under a layer of green leaves until the clutch is nearly complete and incubation begins. After hatching, we record the number of young, the number of unhatched eggs and the number of dead nestlings, if any. Finally, we record the number of young that survived to fledging age from each nest. Obviously, in your martin diary or on your nest record cards, you must record the date of each nest check and the compartment identification number. Through subsequent observations with binoculars or a tripod-mounted spotting scope, we record the age of the parents at each nest (i.e., whether adult male, adult female, subadult male or subadult female.) This is important because younger parents nest later in the season and subsequently fledge their young later, too. Subadult parents also lay fewer eggs, and hatch and fledge a smaller proportion of their eggs and young. Finally, using egg and date data, we determine the clutch-initiation date (i.e., the date the first egg was laid in each nest), extrapolating backwards, when necessary, as we did in Fig. 1, (remembering martins lay only one egg a day). Clutch-initiation date is important because it is needed to calculate the expected fledging date, about 50 days later (i.e., about 5 days of egg laying, about 15 days of incubation, and about 30 days of feeding until fledging). Without knowing the expected fledging date of each brood, a landlord wouldn't know if they had disappeared prematurely, indicating a problem. Check out current research using this data.
|Fig. 1. An example of how a nest record card can be used to keep track of the martins' progress and success in each active nesting compartment. Note that a minimum of 12 nest checks are conducted each season on every nest. Nest checks should be conducted at 5-day intervals during the egg-laying phase of the nesting cycle so that the clutch-initiation date can be determined. After the egg-laying phase, nest checks need only be done every 7 days. Knowing the clutch-initiation date allows an accurate projection of the expected fledging date, approximately 50 days later. Only by knowing the expected fledging date of each brood can you tell if nestlings have disappeared prematurely, a sure sign of predation or other problems, as opposed to fledging on schedule.|
When to Do Nest Checks
The best time of day to do your nest checks is during late morning, or early afternoon, when temperatures are their warmest and martins are away from their colony sites, foraging. Only conduct nests checks during warm, fair weather. During foul weather, both the parents and the nestlings are under the stress of cool temperatures and lack of food. Never stress them further by disrupting their efforts to brood the young, incubate their eggs, or feed their young - you could tip the balance and increase mortality during these times. Always keep the duration of your nest checks to a minimum, because the disturbance will disrupt the parents' normal activities - instead, they will fly around the housing giving alarm calls and a few individuals may even dive past your head. Once you have finished your nest check, walk completely away to allow the birds' routine to return to normal. Avoid doing nest checks just before sunset. If a winch cable breaks or comes off its pulley, you'll need time to make the necessary repairs. Also, if you discover some other major problem, you won't have time to make modifications before dark.
How Frequently to do Nest Checks
During the egg-laying stage, we check the nests every five days. This lets us pin-point the exact clutch-initiation date. After egg laying, we check the nests only every seven days. We cease nest checking when any young in the house are within a few days of fledging - opening their compartment can cause them to fledge prematurely, although this is rare.
What to Do When You Find Problems
While doing your weekly nest checks, you are certain to encounter many situations requiring your immediate attention. If you should have the misfortune of finding a rat snake in one of your compartments, immediately remove and release it alive. Next, start beating yourself up, verbally, for not having had a pole guard in place, because you've probably just lost your entire colony, permanently. The same goes if you should find a raccoon on top of the house, or evidence they had been up the pole (i.e., chewed-off martin wings lying under the house, and blood all over). So, whatever you do, make sure your poles are equipped with guards. If you should find piles of plucked feathers, and/or discover doors pulled open, and/or discover many nestlings disappearing prematurely, and/or find a shed owl feather under the house, you've been hit by an owl. You will need to immediately put owl guards around the outside of your house. I believe owls visit nearly every martin house in North America and once they've succeeded in grabbing a meal, will return night after night until they've wiped you out.
Commonly, while doing a nest check, you will find a nestling (or less commonly, a parent) dead in the nest. Remove their bodies so any surviving nestlings aren't jeopardized by bacteria or disease. It is also common to find eggs that have been kicked out of the nest bowl to the front of the compartment, or out onto the porch or ground. You can discard these eggs - they will not hatch. Martins deliberately remove infertile eggs, or those with dead embryos. Do not place them back in the nest bowl. During a nest check, you also may find nestlings in places they don't belong, like on the ground, or in neighboring compartments. By referring to your nest record cards, you'll be able to return them to their rightful compartments, greatly increasing their chances of survival.
After the eggs hatch, you may encounter two additional problems needing attention: rain-soaked nests and parasites. Nestlings in wet nests can die from hypothermia. If you find wet nests, remove the youngsters and throw out their nests. Replace each nest with a 2-inch pad of dried lawn clippings or fine straw, then fashion a nest bowl or depression in the rear. Put the nestlings back into them. Once you start taking a closer look at your nests on a weekly basis, you may be shocked by the sheer abundance of nest mites, fleas, and blowfly larva you'll see. Tests at PMCA headquarters show that these parasites can prevent the fledging of as many as 50% of the hatchlings. The best and safest way to control nest parasites is to throw them out with the nest. We recommend changing the nests (as described above) on the 2nd nest check post hatch, or when the nestlings are about 10-15 days old.
What You Can Learn From Doing Nest Checks
If you're not monitoring your martin nests, you'll be at a loss to understand and interpret the behaviors you are observing, and will miss out on a great deal of the pleasure that can be derived each summer from hosting these wonderful birds. On the other hand, by keeping accurate records, and knowing exactly what is going on in each compartment, you can learn a great deal about your martins, and the species in general. For instance, you'll learn that adult martins at long-established breeding sites, don't begin nest building until about 4-6 weeks after the first birds are observed back and it takes them one to two weeks to complete their nests. You'll learn that they do not use every nest that they build. Sometimes as many as half the nests never receive eggs because martins seem to get disoriented while building, and construct partial nests in neighboring compartments. You'll learn that they rarely initiate their clutches until lining their nest bowl profusely with fresh, green leaves or pine needles and lay but one egg a day, usually in the morning. You'll learn that adult pairs lay 4-6 (rarely 7) eggs, while subadult pairs typically lay 3-5 eggs, but adult birds sometimes pair with subadult birds. You'll learn that martins don't begin incubation until they lay their penultimate egg, and have an incubation period of about 15 days. You'll learn that all the eggs in a typical clutch may not hatch on the same day, but can have an asynchrony of two to three days. You'll learn that martin eggs are white, starling eggs blue, and House Sparrow eggs brown speckled. You'll learn that martin nestlings fledge 28 to 32 days after hatching. You'll learn that only about 80-90% of the eggs hatch and only about 80-90% of young fledge. However, during cold, wet summers, you'll discover that these rates can drop to as low as 0%. And finally, you'll learn that fledglings may, or may not, come back to sleep in the same (or nearby) compartments for a week or so, after fledging.
If every martin landlord in North America would start managing their colonies in a more "hands on," responsible manner, I believe the martin population would double or triple in just a few, short years. Landlords who haven't yet begun monitoring their martin boxes, out of fear of scaring their birds off, can look forward to greatly increasing the number of young they'll fledge each year, if they'll just take the nest check plunge. I strongly urge everyone to get more involved in their hobby by doing weekly nest monitoring. It's the most important, beneficial thing you can do to help the martins in your care.
Additional Nest Check Tools
James R. Hill, III, is the founder of the Purple Martin Conservation Association and editor of the Purple Martin Update. He is landlord to over 160 pairs of martins.
Copyright 1992 by Purple Martin Conservation Association. All Rights Reserved.
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