Understanding How Owls Raid Purple Martin Gourds And Houses

[Steve Kroenke]

Understanding How Owls Raid Purple Martin Gourds And Houses

The wild hoots of the barred owls often filled the nights at my old home site in Wacissa, Florida and they are still with me. Oh, how I enjoyed the barred owls talking to each other. Their loud and somewhat scary calls reminded me of nature in the raw and horror movies. And how true that proved to be! Their calls now have a different meaning to me and I no longer wish to hear them anymore. For me, the barred owl?s wild hoots mean death and destruction to any purple martin colonies located in the owls? hunting territory. The bright lights shining on my martin colony at night revealed the large sinister shapes sitting on the gourd crossbars. The terrors from the darkness weren?t there to rest; the barred owls had come to feed.

EVERY martin colony I have managed in Florida were I previously lived has been hit by barred owl predation, resulting in the deaths of numerous, possibly hundreds of adults and young. Though I have learned a lot about owls over the years and have installed various owl guards on my gourd clusters and houses, the destructive capabilities of these ferocious predators can?t be underestimated. They can inflict enormous damage to a martin colony either through killing the martins or causing them to abandon the site. It seems like all my Florida colonies have been cursed with the barred owl hex!

Two Main Killers

The two main owl predators of purple martins are barred and great horned owls. The barred owl has a large round puffy head, huge moist brown eyes and is barred across the chest and streaked lengthwise on the belly. There are white spots on the back. This owl is between 17 and 24 inches in length and has long legs. The male owl is smaller than the female. When these owls hoot, it can sound like some demon straight from the Underworld! If you have never heard one up close in the dead of night, be prepared to say the Lord?s Prayer because you will think your time on this earth is about to end! Barred owls are found primarily from east of the Rockies north to Canada and as far south as Central America. In the United States, barred owls are very common in the Deep South. These owls prefer to live in woodlands, swamps, river bottoms and like to be near water. Since they usually nest in large natural tree cavities, stands of old timber probably provide the best habitat for barred owls. They will sometimes nest in abandoned hawk or crow nests.

The great horned owl is truly the great white of the owl family, a ferocious predator. This owl has ear tufts or horns and is heavily barred beneath with a conspicuous white throat bib. The great horned owl is between 18 and 25 inches in length, has long legs, and the male is smaller than the female. For such a powerful owl, its hoot is not such a powerful thing when compared to the barred owl. The great horned owl emits a rather low-key series of weak hoots. This owl has a huge geographical range throughout the United States and Canada up to the tree limit and way down into South America. These owls inhabit forests, woodlands, thickets, swamps and open country. Great horned owls seem to be more versatile in habitat preferences than barred. Great horned owls usually nest in abandoned hawk, crow or heron nests, but will also use tree hollows, and occasionally nest on the ground.

Size Of Owl Territory

Both barred and great horned owls have breeding territories that may average about one square mile. They know their territories well and will eventually find any martin colony located inside. The territory size may be more or less depending on the vegetation type, availability of water and nesting sites, prey abundance, and number of owls. The great horned owl is more dominant and a large female could kill and eat a small male barred owl. Also, young barred owls would be candidates for great horned owl predation. The territories of different species can overlap some though both barred and great horned owls tend to stay out of each other?s way.

Is Your Colony In Owl Habitat?

These owls can be a serious problem for martin colonies located near timber, woodlots, swamps, rivers, lakes, open pastures with scattered trees, and even tree canopied suburbs and residential areas. They are common and seem to be increasing in population in some areas and expanding their nesting range. Both species have become urbanized and even nest in city parks. However, each needs appropriate sites for nesting. These two owls, particularly the great horned, nest in EVERY state where purple martins colonize. Few areas would be immune to owl attacks, though some probably would have a lower risk. For example, martin colonies located in beach coastal areas with very few trees and large expanses of open sand and, of course, salt water, would probably have limited chances of owl attacks. Colonies located in large open pastures with few trees nearby may have a lower risk of owl predation. Such an environment may not offer sufficient large natural nesting cavities or tree growth to support a family of owls. The barred owl is probably more limited in habitat requirements than the great horned, so most martin colonies would be more susceptible to great horned owl predation.

How Owls Find Martin Colonies

It is a matter of sound and sight and the owls excel in both categories at night. These owls have extraordinarily sensitive hearing abilities that would rival the most sophisticated electronic tracking devices known to mankind. The ears of all these owl species are perfectly designed to detect sound and lead the owl to a potential prey source. The feathers around the ears form a concave surface, somewhat like a satellite dish that captures and funnels sound. These sounds are then transmitted to the brain where the owl deciphers the location and possibly the type of the potential prey. All these owls can pinpoint a possible prey item with precision like accuracy and they do NOT need their keen nighttime vision each time. It is almost like they have an auditory Global Positioning System in place! All they need are the sound waves of a squeaking mouse, a hopping rabbit or?the calls and night noises of martins safely sleeping in their nests. The owl tracks the sounds like a wolf on the trail of a deer. The great horned and screech owls have ear tufts and these horns help the owls look bigger to ward off possible predators. Makes them look like avian devils! The tufts do not enhance these owls? hearing abilities. The barred owl does not have ear tufts and its head is round.

The eyes of the owls are super sensitive, too, and may be as much as 100 times more efficient than humans under dark conditions. Owls have binocular vision, large retinas, and their eyes contain a superabundance of rods that are light gathering cells. Rods are used in dim light conditions. The other retinal cells are called cones and these operate in bright light and are related more to color differentiation. Owls have fewer cones. Owls don?t need to delineate colors during the night nor hunt in bright daylight. They look for still or moving shapes. At night, owls can see small animals scurrying along the forest floor, the shapes of roosting birds, and the movement of martins or their still silhouettes in those horizontally shallow nest cavities with holes only one inch above the floor. But owls can?t see in total darkness and rely more on their keen hearing abilities to locate prey later in the night.

Purple Martins Advertise Their Location At Night And The Owls Are Listening

Purple martins are noisy birds, particularly during the day, and this is a common trait among most colonial nesting species. But martins continue to make various sounds during the night and early morning hours and this is often their downfall when owls are hunting in the area. Male martins emit the familiar gurgling call to their mates to perhaps reinforce the pair bond and advertise their territorial dominance. I have heard these calls all during the night and into the early morning hours. I have stayed up all night on a number of occasions chasing barred owls away from my colony. I was amazed at the amount of singing by the male martins. One male would gurgle and then another would answer. And these were LOUD vocalizations that spread rapidly in the excellent acoustics of the night. Male martin nocturnal vocalizations greatly intensify after pair formation, during nesting building, and continue during the egg incubation period. Perhaps the most dramatic and intense male nocturnal vocalizations occur during dawn singing, which is a period of time that both ASY and SY mated males make these calls to attract SY females. The males start their vocalizations at around 4:00 am and continue for a good while still in their nests. Males will do this while sitting upright in the nest holes or even on porches. Then they leave to continue the singing in the sky above the colony.

Martins frequently rustle in their nests as they scratch at parasites or snap their beaks at annoying mosquitoes, creating a popping noise when their mandibles come together. Martins also hit against the aluminum room dividers and the knocking noises are very noticeable. Large young can be heard emitting the food begging vocalization, chooo, chooo, chooo way into the night, sometimes as late as 10:00 pm. These begging calls may resume early in the morning while it is still dark. All these various martin vocalizations and other sounds are easily detected by hunting owls.

And purple martins do NOT stay still during the darkness, particularly early in the mornings. After the owl has located the martin colony because of the martin nocturnal vocalizations/sounds, then the owl also uses its equally impressive night vision to find prey. The male martins begin the dawn singing chorus at around 4:00 am and will often sit near the entrances to their nests. Other males will sit upright in the holes and just pour their hearts out. Martins may come out in the early mornings on porches if they are attached to gourds or part of houses. This is exactly what any hunting owl is looking for, particularly if the owl has been predating the colony for a while. The owl knows there is food there and he learns to sit on gourd crossbars, house roofs or perches, or nearby trees and watch for the martins to make their early morning appearances. Then the owl starts attacking any martins that are near their entrance holes or on exposed porches.

Male Owls Hunt For Their Mates And Small Young

If your martin colony is located in the hunting territory of a great horned or barred owl, then it is only a matter of time before one comes to investigate all those night sounds emanating from your gourds and martin houses. In my colonies, the earliest I have experienced barred owl predation that I was aware of, was the first week of March. During this time in north Florida where I lived, many adult male martins are paired and mated males are more vocal at night than bachelors.

This time also coincides with the nesting of the barred owls in the north Florida area. The male owl, like male hawks, is the primary food provider for his mate and his small young. The female owl incubates the eggs and broods the young while her mate hunts for food. So he has a lot of mouths to feed including his own. A martin colony becomes an easy and ready food source for the male owl and he is probably responsible for most attacks early in the season. Since he is smaller than the female, he is better at raiding martin gourds and houses.

When the young owls are larger, then the female starts hunting, too, so you may have both parent owls raiding your colony later in the season. They may even bring their fledged young to the feast. I have seen as many as three barred owls sitting together on my gourd crossbars at night. When several owls are attacking, the carnage they can inflict is unimaginable. I would sometimes find martin feathers scattered from one end of my yard to the other.

How Owls Raid Gourds

When an owl has picked up the sounds coming from a martin colony, he may first fly to a nearby perch, as owls like to survey the area. This can be a tree, post or similar perch. The owl will listen and try pinpoint the potential prey using his superb auditory skills.

Eventually, he will fly to the gourd crossbars or any perch above the crossbars. Then the trouble begins. Crossbars are ideal perches for owls to launch attacks on gourds. I often shine bright lights on my colonies so I can see and chase owls away. The lights DON?T discourage the owls at all. These lights have revealed some of the terrifying secrets of the owls? hunting techniques and I have observed their hunting behavior on several occasions. I have seen three different modes of attack by barred owls on gourds and I?m sure there are others. These same behaviors may apply to great horned owls, too, but I haven?t experienced their predation directly on adult martins, just fledglings roosting on exposed gourd crossbars. Here is what I have observed over the years?

Hummingbird Maneuver

As the owl sits on the crossbar or perch, he listens for sounds inside the gourds. You may see him turn his head almost completely around as he tries to pinpoint the location of possible prey. If he is sitting on a crossbar, he may walk like a parrot as he surveys the gourd cluster. His first visit to a gourd cluster is surely a learning experience as he tries to figure out those white things that are hanging down from the crossbar. But he knows there is food in them; the martins give themselves away. He may bend over as he listens. I have seen a barred owl bend almost parallel to the crossbar as he stretched as close to the gourd as possible without losing his grip. He may hop off and begin to flutter or hover like a hummingbird right in front of the gourd entrance hole. He may be trying to see inside. If the gourd is shallow, he may see any martin moving inside in response to the owl?s hovering motion. Such martins may become terrorized and bolt from their gourd and right into the owl?s talons. Since barred owls are cavity nesters, they look for holes and know exactly how to cling to them. So he tries to grab the entrance hole or rain canopy. If he succeeds, adult martins, particularly males and also females without eggs/young, panic and immediately try to escape out the hole. Remember: martins are birds of the open skies and they fly from danger and do not hide in thickets, trees or gourds. The owl is now hanging by one foot on the swinging gourd, and he is beating his wings to stabilize himself. This action produces total horror for the martins. The martin tries to escape out the entrance hole that is partially blocked by the owl?s talons and possibly his breast that could be pressed against the front of the gourd. The owl may feel the martin struggling at the entrance hole. So he either hooks the martin with his other free foot that may be scratching at the entrance hole or he releases his foot at the entrance for just a second, hovers and then grabs the exiting martin.

Reach Down And Grab Method

If gourds are suspended close to the crossbars and these gourds tend to have short necks, then the entrance hole may be within reach of an owl?s long legs. This is particularly true with smaller gourds. In this situation, the owl is perched on the crossbar above the gourd. The owl then climbs down to the gourd entrance hole by holding onto the crossbar with one foot. He then hangs downward and uses his free foot to scratch at or even enter the gourd entrance hole. I saw this behavior only once when a huge barred owl tried to raid a small plastic gourd at one of my colonies. The distance between the crossbar and the gourd entrance hole was about eight inches. This owl would bend over, hold onto the crossbar with one foot, slide his body down, and then try to grab the entrance hole. I did not let the owl complete the attack and chased him out of the yard. The reach down and grab method may be used more than I suspect, as owls have long legs and are very good at hanging on perches or porches.

Swoop In Method

This is a straight forward attack technique and the owl simply swoops in lower than the gourd cluster, pulls up to the front of a gourd and grabs the entrance hole or rain canopy or martin quickly or uses the hummingbird method first. I have observed an owl try this several times and on one occasion the owl hit the gourd rather hard but was unable to hold on. I could hear the owl?s talons scratching on the painted gourd surface when he tried to grip it. Usually the owl is sitting on a nearby perch such as another gourd crossbar, martin house roof, or tree. He sees martins moving in a shallow gourd or the entrance hole or hears their night sounds and then launches his swoop in attack.

How Owls Raid Houses

Owls use somewhat similar methods to raid martin houses, particularly the hovering, hanging and swooping techniques. I have seen these attacks several times on both aluminum and wooden houses. During his first visits, the owl usually lands on the house roof or roof perch. Just like with gourds, the owl listens for sounds coming from the house below. Eventually he hops off and begins to hover around the house, as he sizes up the situation. He may be looking inside the holes, particularly those houses with small 6x 6 compartments with nest holes only one inch above the floor. The martins in such houses are highly vulnerable, particularly compartments constructed of bright shiny aluminum or those painted white inside. These environments enhance the visibility factor inside the nests. The house porches and any railings provide a perfect platform for him to cling to or even sit upright on. He then grabs the porches and railing and hangs there. This action typically shakes the house and he even may be beating his wings to keep somewhat stabilized. Martins begin to panic and start pouring out of the house. During these exits the martins may strike the owl?s breast or hit his wings and he tries to grab them. He also scratches at the entrance holes as he attempts to snag the adult martins as they flee. If he is after young martins, he may insert his long legs into the nests and drag the babies out. These attacks create total terror for the adult martins and if the house is well populated, then the owl will usually get a bird each visit. After a few attacks, the owl may forego perching on the house roof and just swoop in and hit the house, hang or hover there, and start grabbing for the martins. Any martins that are perching or roosting on the outside porches are readily taken during the night or early morning hours, as the owl will use his excellent vision in these cases. I once saw a female martin just after dusk sitting on a guardrail that was next to a porch divider. The martin never made it through the night. One moment she was there and the next she was gone, grabbed by a barred owl. The owl hit the house so hard that the aluminum porch divider was bent almost down to the porch.

Physical Signs Of Owl Predation

Natural gourds that have been raided may be broken at the entrance hole, leaving a noticeable gap when the martin is forcibly pulled out. This is particularly true of thin shelled or older gourds. Gourds may have scratches on their fronts around the entrance hole. One of my gourds had talon punctures that penetrated all the way through the gourd shell around the sides and bottom of the entrance hole. This gourd was also cracked on one side of the nest hole. Sometimes during extremely violent attacks where the owl has grabbed a martin at the entrance and the martin is difficult to pull through the small nest hole, the gourd may be twisted on its hanging wire. This happens as the owl is wildly flapping, twisting and pulling at the gourd. I have had gourds turned sideways during such attacks.

Plastic gourds will have little physical damage, but may on occasion show a scratch mark around the entrance hole. You may see material hanging out of the nests. Again, violent owl attacks may twist the gourd on its hanging wire.

Thin aluminum rain canopies above the gourd entrance holes may be bent downward. This is particularly true on canopies that extend out several inches. I had one canopy that protruded out nearly 4 inches, and it had a noticeable indentation after the gourd was raided by a huge barred owl.

If the owl has raided a Trio aluminum house with those flip up door panels, then you may see doors pulled ajar or even wide open. I have had the doors completely pulled off and carried away by barred owls. The thin railings of the Trio Grandpa house may be crushed down from the weight and power of the owl.

For houses without flip up door panels, you may see nesting material pulled out the entrance holes. If your house has thin railings or perches, these may be bent or even broken.

There may be other physical signs of owl predation on both gourds and houses. This could include blood smears around the entrance holes with martin feathers stuck there. Sometimes a martin will be lodged in an entrance and have visible talon wounds on its head or breast. I have seen that situation several times in both gourds and houses, particularly with srehs. On rare occasions, an owl will grab a martin for just a second at a gourd entrance hole, the owl will lose his hold, and then the martin falls back in and dies right there. When an owl is violently twisting about to dislodge a martin from either a gourd or house compartment, the owl may lose a feather. You may find owl feathers on the ground underneath your gourd clusters or houses. If the owl carries the martin to the ground or to a nearby perch, you may find plucked martin feathers and even regurgitated food pellets. Many times the barred owls would carry off the martins from my colonies, particularly early in the season, as these were males that were hunting for their mates and young. For later season attacks, the owls often ate the martins at the colony site, leaving plucked feathers scattered under the gourds and houses.

Behavioral Signs Of Owl Predation

There are several key martin behavioral signs that will TELL you something is bothering the martins at night. First, are your martins highly nervous about returning to roost in the houses and gourds? This is particularly true early in the nesting season before martins have eggs or young. This is NOT the typical hawk fright response where martins circle high above the colony until late and then come screaming down all at once to their nests. This pre-roosting owl fright behavior is different. You may see your martins land on the houses and gourds then fly away. They stay there a few minutes, and then bolt. They make repeated back and forth flights and seem hesitant to stay. The martins don?t socialize in the late afternoons around the colony. They are definitely nervous. Finally, they may enter their nests, but some start leaving right before dark and these DON?T come back. This leaving before dark behavior is one of the best signs that it is an owl bothering the martins at night. I have seen this behavior over and over again at my colonies that had repeated owl attacks, particularly early in the season. The martins would return and enter their gourds and houses at roosting time. Then just before dark, many martins would start leaving and flying as fast as their wings would take them away from the horrors of the night.

Most disturbing to me has been the death screams of martins being killed at night by owls. It is one of the most horrible sounds you will ever hear and I sometimes find myself shaking afterwards. I still can?t accept it. That is how martins let you know at night that an owl is attacking. I used to leave my window open in my bedroom so I could rush outside when I heard that death rattle. These screams were so loud that I was awakened from sleep. As a martin emits its final death scream, other martins may bolt from the gourd cluster or house. I have seen that happen. Sometimes an owl would carry off a screaming martin and I could still here the cries as both disappeared into the night. The night and early morning acoustics are excellent for the transmission of sounds and the death screams of martins being butchered alive by owls has greatly disturbed and emotionally affected me.

Repeated Owl Attacks Can Result In Total Colony Abandonment Before The Young Hatch

If you have a small colony and everything is fine one night, then the martins do not return the next or they return and then leave, then you most likely have an owl problem. Small colonies are particularly prone to total abandonment after several nightly visits from owls. After repeated owl attacks martins like all birds have survival instincts. If a colony site is under nightly siege from owls and martins are fleeing for their lives in total darkness during the early nesting season before eggs or young, then the martins will often abandon the area. Why would any martin subject itself to constant nightly torment or endanger their lives? This instinctively tells the martins that the site is UNSAFE. If martins have eggs, then the females in particular will stick it out, at least for a while. The males may quit roosting. But even the females may eventually desert their eggs when under constant owl pressure at night.

Owl Attacks After The Young Have Hatched

Martins will NOT abandon their babies because of owl attacks, but the adults, particularly the males may quit roosting at the colony. Female martins will NOT abandon their young babies at night so this places the brooding females in grave danger from the owls. I have lost in the past numerous female martins that were forcibly dragged off their babies or were killed and left lodged in gourd or house entrance holes. Owls may concentrate on pulling out the young later in the martin nesting cycle when not as many adults may be roosting at night, and houses are more vulnerable in these situations. The owls can more easily hang on a house with porches, reach into the nests in those compartments with nest holes only once inch above the floor, and then feel around for baby martins. Owls have a much more difficult time doing this with vertically deep gourds without porches.

Owl Attacks On Fledged Young That Roost On Exposed Gourd Crossbars Or House Porches/Perches

Nothing is more attractive to an owl than a large collection of young martins roosting close together on exposed gourd crossbars or house porches/perches. This is a food bonanza and owls will hit these colonies over and over again until all the martins may quit roosting in the open.

This situation usually exists at large colonies where most of the adults bring their young back to roost at night. Many of the young will be led directly inside their gourds and house compartment by their parents. However, other babies will roost together in the open on the crossbars or house porches/perches. I have had several hundred young martins roosting on gourd crossbars, particularly the lower tier in multiple stacked gourd clusters. The young would huddle together toward the gourd pole so that they would not be as exposed on the outer perimeter. The huge barred owls would swoop in and grab baby after baby off the crossbars, sometimes dislodging several other babies during the process. The more independent young would often flee for their lives into the darkness while the recently fledged babies would not. Not a single adult martin roosted with these young on the exposed gourd crossbars, and in fact, most of the adults would not remain at the colony after they had brought their young back. After several nightly hits by owls, many of the young would flee into the darkness. The adults continued to bring the young back to roost inside the gourds and houses, but after a while, many of the older babies quit roosting together on the outside. The owls attacked on and off all night long.

At my current home in northwest Louisiana in 2005, great horned owls attacked and killed many martin fledglings that roosted on gourd crossbars and house perches at my neighbor?s colony and mine. I would find numerous piles of plucked martin and occasional great horned owl feathers littering the closely mowed lawns under our martin housing.

What May Work Or At Least Minimize Owl Predation: Physical Guards And Gourd/House Compartment Designs

The key to minimizing owl predation on gourds is to block the immediate air space in FRONT of the gourds so that the owl has a difficult time reaching the entrance holes. There are various methods you can use and they are described in detail in the Forum Archives. These methods typically involve installing curved metal rods or some kind of fencing/baffle out from the crossbars above the gourds. These guards then bend downward in front of the gourds, blocking the immediate area around the entrance holes. Wires can be strung across the gourd crossbar tops to create a spider web pattern and this makes it difficult for owls to hover inside the gourd cluster. The martins are small enough to fly up underneath these guards to reach their nests.

However, these guards will not necessarily stop a determined barred or possibly a great horned owl from still trying to get to the martins inside the gourds. Though I used such guards for some time, barred owls continued to pester my martins every year. The attacks nearly always begin in mid March and will continue on and off throughout the season. Once an owl hears the martins in the gourds, he may try and try to get to them and such efforts may still cause the martins to flee into the darkness. These owls may go into a feeding frenzy trying to raid the gourds that are protected by guards. The owl may hang on the metal rods or fencing that protrude out in front of the gourds. One year I saw a huge barred owl hanging upside down as he gripped with both feet a double metal rod guard that protruded about a foot out in front of a supergourd! I frightened him away, so I am not sure if he would have succeeded in reaching the entrance hole. The martins nesting in that gourd abandoned their nest shortly afterwards, leaving behind several eggs.

For total gourd cluster protection, a complete cage or prison can be installed around your setup, but such a barrier is heavy and probably difficult to build and attached. This will add more weight and subject the gourd cluster to greater danger of being toppled during windstorms.

Using gourd designs that emphasize significant vertical/horizontal depth, particular gourds with offset holes or curved PVC tunnels or a hole in the natural neck funnels, may do a good job of protecting young martins and females that are incubating eggs or brooding babies. However, if the owl can reach the entrance hole and grip a part of the gourd, then such physical action will still often panic male martins and non-incubating/non-brooding females. The martins may try to escape out the entrance and right into the owl?s talons. The greater the distance from the entrance hole with a corresponding reduction in visibility from the outside produces the best protection for martins residing in the nesting chamber of a gourd.

For houses, using offset holes as entrances to double nest-chambered compartments provide good protection for the babies and incubating/brooding female martins. This creates considerable seclusion for the nesting chamber and the martin inhabitants and insulates them from the outside entrance hole. Such females tend to remain tight on their eggs and babies even if owls are creating an outside disturbance. Males may still panic and try to escape. Just having a large horizontally deep, but vertically shallow compartment where the hole is cut on a front panel still permits owls to see to the back wall. An owl can hang on the porch, reach in, grab nesting material, and create total terror for the adult martins. The reach of a huge barred or great horned can probably extend to nearly a foot and both adult and baby martins are at risk. Male martins and non-incubating/non-brooding females may still panic and try to escape when a huge owl is hanging on the house, shaking it, and scratching at the entrance holes. There are articles in the Forum Archives that described how to create double nest compartment configurations in your houses.

You can attach fence guard panels to the fronts of houses to at least keep the owl at some distance from the entrance holes. This is the 2 x 4 fencing that you install to the front panels of your houses, preferably vertically long. Again, the Forum Archives provide descriptions of these owl guards. If you can, it is better to have these panels extend out several inches from the porches so that the owl will have an even greater difficulty in reaching the entrance holes. Barred and great horned owls can STILL grip these fence guards, hang there, and create a lot of disturbance to the roosting adult martins. These owls can easily reach through the fencing and partially into the nest hole. Remember: they have very long legs. At my previous home in Tallahassee, Florida, a large super martin colony down the road from me was exterminated by barred owls and the landlord used such fencing on his T-14 houses. Barred owls would hang on the fencing and grab the martins as they struggled to exit the oblong srehs.

A step beyond the fence panels is the complete cage or prison approach around your house. This provides complete coverage and would surely keep owls away from the entrance holes. Such a barrier may be more difficult to build and add more weight to the house.

Another promising method that has worked for me involves installing complete outside entrance hole blocks to the front house panels. This is more easily done with hexagonal houses or houses with separate porches. This involves attaching an aluminum or thin wooden strip from the bottom porch to the top of the house on each side. This strip can be from three to five inches in width and completely blocks the nest hole from view and effectively keeps any owl from reaching inside the entrance holes. There is still plenty of room for the martins to enter their nests by simply landing to the side of the block on the porch and then crawling behind the block on the wide porches to reach the entrance hole. Most porches are around three inches wide, so the distance between the outside block and the entrance holes is plenty open to allow martins to freely enter and exit. I used this method on several old Heath houses a long time ago and the martins readily nested in them and the owls were unable to reach in the nest holes and rarely tried. The owls were unable to see the entrance holes it seems and that may have discouraged their attacks. What I had was a six side hexagonal house with six bottom to top front panel blocks attached to the outside porches. The nest holes were blocked from direct view, but could be easily entered by the martins by going around the guards and walking along the porch.

The main problem with this approach at established colony sites is that such blocks may interfere with your monitoring of the nest compartments. But I?m sure you can attach continuous blocks with removable clips or something similar. Another potential issue concerns unestablished sites. Since the nest holes are directly blocked from easy view unless you look to the side of the guards, then investigating martins may not recognize such a house as a possible nest site. But martins have been so conditioned to martin houses on poles, that this may not be a problem. Martins will land on houses that have doorstops that completely block out the nest holes. And finally, owls may still hang on such protected houses and create disturbances, resulting in martins panicking and flying out the entrance holes.

Using Sound To Deter Owl Predation: Remember, Owls Find Martin Colonies Initially By Sound

The most promising solution to owl predation, in my opinion, may be a sound deterrent system that attacks the owl at the auditory level, as owls primarily hear the nocturnal vocalizations of martins to initially find them. This should be done as a preventative measure PRIOR to any owl predation and not AFTERWARDS.

At my previous colony in Tallahassee, Florida, I used a sound deterrent system in 2002, 2003, and 2004 by installing an outdoor speaker within ten feet of my colony site and playing music from dusk to dawn throughout the nesting season. I did this BEFORE any owl predation had occurred and I can promise you it would have happened. I played progressive/hard rock music at volume 4 to 6 on a scale of 1 to 10 and that did an excellent job of masking the male nocturnal vocalizations and perhaps creating auditory dissonance for the barred owls that frequently hooted nearby. The owls NEVER recognized the site as a potential food source and to the best of my knowledge NEVER visited the colony. For those three seasons, I did not have a single instance of owl predation. This is a miracle. On a number of nights and early mornings, I stayed outside to listen and observe. Though I could still discern the male vocalizations if I was directly inside the colony site and under the houses/gourds, the music did a great job of diffusing these martin calls. I could detect nothing at a good distance from the colony. On a number of occasions, huge barred owls flew high OVER the colony site during the early morning hours, but they NEVER swooped in. The loud music seemed to create its own auditory force field that may have kept the owls at bay. The owls would sometimes hoot from the tops of trees within several hundred feet of the colony site. I would go to where the owl was hooting and I could still hear the music playing and hopefully masking any purple martin vocalizations and other sounds.

The loud music did NOT adversely impact the martins at all. Later in the season, the parent martins would bring their young back to roost in the houses/gourds and sometimes the recently fledged babies would sleep on the crossbars. In the past, this was suicide as the owls slaughtered the babies all night long. However, sound may not override the visual stimulus of fledgling martins roosting in large numbers on exposed gourd crossbars. In these cases, probably nothing would work as the owls could see their prey and not use any sound to locate the martins.

I believe that the ultimate and most effective owl deterrent system will use sound as its primary mechanism. We need to create an auditory barrier within our purple martin colonies that attempts to achieve one or more of the following objectives: (1) Mask all purple martin nocturnal vocalizations/sounds so the any owl NEVER even recognizes the colony site as a potential food source. (2) Create auditory dissonance that overloads or confuses the owl?s incredible, sensitive hearing ability so that he is unable to distinguish purple martin sounds and launch predatory attacks. (3) Create an auditory environment that may both frighten and produce unpleasant auditory sensations for the owl. The owl must be attacked at the auditory level because that is his primary technique for finding and then raiding purple martin colonies. This can be loud music or perhaps white noise such as running water, buzzing, and humming or similar sounds. The area of sound deterrence needs to be more fully researched relative to the variables of sound type, volume, distance from colony site, and duration.

Many years ago I tried a similar but ineffective method of using sound to stop owl predation that was ALREADY in full progress. The barred owls were inflicting significant carnage on my large colony and had already about destroyed it. I tried playing loud hard rock music (using my favorite band?s music, Led Zeppelin) out my bedroom window. But the music was not close enough to the colony site to truly impact the owl?s hearing ability. The distance between the window and the closest gourd pole was around 50 feet; this was much too far. Plus, the owls KNEW there was food at the colony site. However, if I had placed an outdoor speaker directly in the colony and turned up the volume, then that may have frightened the owls away.

By placing one or more outdoors speakers on poles DIRECTLY adjacent gourd racks and houses, this action should do an even better job of creating an auditory force field around the colony site and masking purple martin nocturnal vocalizations and sounds. Remember: owls primarily find martin colonies by sound. If the owls can?t hear the martins at night or in the early morning hours, then they may not visit the colony site. And even if the owls see the martins flying about in the evening prior to roosting, the owls still mainly rely on their acute hearing to find the martins initially. If the owls can?t hear anything or discern martin calls that are interwoven within loud music or white noise, then they will have a difficult time pinpointing gourds/house compartments for raiding.

Owls And Purple Martin Colonies: A Recipe For Disaster

Purple martins nest in dense colonies within the restricted environments of gourd clusters and multi-room houses. This is the perfect set-up for a massacre by owls. All the prey is close together, making noise and triggering the hunting instinct in watching and listening owls. We have created such nesting situations for martins with gourds and houses, particularly using horizontally shallow cavities, which allows owls to see and reach inside. Martins nested in the prehistoric past in the east as single pairs or in isolated groups in abandoned, vertically deep woodpecker holes. Such a nesting arrangement is far less vulnerable to owl predation as owls can?t see or reach the martins deep down inside. Also, deep woodpecker cavities in dead trees with thick outer walls may be more sound proof than material such as aluminum, plastic, natural gourds, and commercial wood products. This may reduce the amplification of the male martin nocturnal vocalizations. A shallow aluminum compartment in a martin house may create an almost megaphone for the transmission of martin calls/sounds during the night and early morning.

With Accipiter hawks and falcons, martins have a good chance of escaping. It is one flying machine against another and the martins usually win as long as they know the predator is after them. Martins can usually see their enemies and they know what to do to escape: they were born to fly and not hide.

But owls are MUCH different for purple martins. The owl hunts during the night when martins can?t see their enemy. The martin is helpless and trapped in its gourd or house. All the martin can do is flee in terror in the darkness and try to avoid those terrible talons. Owls and martins in the black night: a recipe for disaster and carnage. And owls are nesting EVERYWHERE purple martins breed. All martin landlords should become knowledgeable of owls and how they raid martin colonies. Be sure to take measures to protect your martins or at least reduce the chances of owl predation through installing guards to your gourd clusters and houses. It will be only a matter of time before a huge barred or great horned owl hears your martins at night and comes to pay a deadly visit.

Steve Kroenke

[Jim Koenig]

Steve, first let me say thank you for the time and effort you spent on posting your thorough and informative article on Owl predation.

As a teenager in Minnesota (more than 30 years ago) I had several successful colonies of martins. I lived in a small town with several large colonies nearby and had no difficulty starting my own. To my knowledge, we experienced no owl or hawk predation while I was there.

Now I live in the country and the nearest martin colony is several miles away. I put up a T-14 last year along with 4 super gourds suspended under it. On Memorial Day, a pair of first year martins arrived and they hatched 4 young in one of the gourds. Eventually 3 fledged--I don't know what happened to the other baby--it was in the nest for two weeks and then disappeared without a clue.

This year I am hoping for more residents in my martin house. Your words about owl predation however has me worried though. My home and the martin house is in the middle of a two acre clearing that is substantial surrounded by woods. These woods have both barred and horned owls. Every night I hear them hooting. Last year, I felt that I didn't want to put up any owl guards to minimize possible deterence that they might have on attracting young martins looking for a home. This year, I intend to put owl gaurds on the gourds.

Before I read your article, I felt the T-14 itself was fairly safe against owl attacks. It is made of 7/8 cedar and is very solid (and heavy.) I felt the cavities were deep enough to keep talons away from the back half of the cavity and the structure was so solid that the most vigorous wing flapping would excite only the most skiddish of martins.

Nevertheless, after reading your article, I can see that placing a 3 inch wide barrier directly on the edge of the porches in front of the holes would make a great deal of sense for these reasons: 1) it prevents the owls from seeing deeply inside the cavities, and 2) they can't easily get their legs into the cavities or opening, and 3) any fleeing martin would double their chance of a successful escape since the owl can't cover both exit paths at once.

Could you or any other informed person please comment on when is the right time to place that type of owl guard on a T-14? I understand Steve that your present location makes finding new residents easy. However, in my area, new residents are difficult to obtain. Should the guard be placed there after the eggs are laid or hatched? I worry that the otherwise highly visible holes on my white house will not be seen from the sky and therefore new martins looking for a home may pass me by.
Thanks!

[Steve Kroenke]

Hey Jim,

The T-14 design with its deep cavities no doubt gives greater protection to the martins from barred and great horned owls. If you use srehs, then these restrictive entrances will most likely keep the owls from reaching inside as their feet are probably too large. However, these houses are not immune to owl predation. When I lived in Tallahassee, Florida, there was a wonderful super martin colony (almost 100 pairs of martins) located about 4 miles down the road from me. I often rode my mountain bike down to visit the landlord and share information with him. He used a combination of plastic gourds and T-14 houses. His T-14s had the srehs. However, his colony was completely destroyed by barred owls, Cooper?s hawks and rat snakes in spite of deep cavities, srehs, snake baffles and external owl guards. I helped him install the 2? x 4? wire panels all around his T-14s to keep the owls from reaching the entrance holes. These ?open? baffles did not work as the owls can still see the martins in the entrances and the owls can fly to the wire, hang on it, and grab the martins as they try to escape. I am sure other folks have had good success with the wire panel approach as owls do vary in their determination and effectiveness in predating martin colonies.

I do believe the external solid baffles that are attached to the outside porches and block visibility inside the entrances are better. These keep the owls from seeing the martins in their nests or near the entrances, block the owls from grabbing the entrances, and give more seclusion to the martins. One drawback is that these baffles could also block the entrances from martins which could be looking for housing. However, martins are so conditioned to look for ?houses on poles? that they would probably still visit.

What you could do is try the external solid block guards this season and see how any martins respond to it. Martins could still see the entracnes from a side view. Some folks have even installed various owl guards such as the wire panel approach after martins are already nesting. At my friend?s colony, we attached the wire panels to the T-14s even though some of the female martins were already incubating eggs. It took about 30 minutes for the martins to adjust to the houses. No martins abandoned their nests. The martins were at first hesistant to fly "through" the wire baffles. But soon they were all going through them to reach their nests.

Good luck with martins this year.

Steve

[steve r]

Steve once again this year Im using power horns in my gourd racks. I run speaker wire down the poles to a radio set on a timer. I set the timer to come on just before dusk and go off just after dawn. It work very well last year no owl attacks.

[roblrich]

Anyone know of the 'Oakwood Game Farm NiteGuard' that suppose to be able to protect PM colonies from Owls? Any thoughts about it? Seems much cheaper and easier than installing owl guards.

[Emil Pampell-Tx]

Robert, I ain't buying nothing until several people tell me that they have worked for several years...Most of that stuff is junk, it works for about 2 weeks...Please don't use my reply for not trying it, I would like to see someone else try all of those kind of things, I don't want to waste my money, so I will wait a while, and good luck if you do try it

[roblrich]

Yea, you are probably right Emil. But anything that would work would be better than subjecting your colony to 'Led Zeppelin' all night. How many dead PM's did Steve find each morning that hung themselves? I am thinking about setting up a system and playing music as a deterrent. But geez, let's think of some better music to culture our good friends the Purple Martins.

Maybe they would prefer Frederick Chopin, Richard Strauss, Piotr Tchaikovsky, heck Mozart would put anyone or anything to sleep. And you could wake them up with some simple Beethoven.

Or let's get down with some blues. Play some Skip James, Joe Bussard, or even simply BB King. Want something more contemporary? Then maybe some "Ratpack"? OK, no Sammy Davis Jr, but good ole Frank Sinatra or Dean Martin would do the trick.

Listening to these guys sounds more interesting than owl guards. But my PM's and I will draw the line at Led Zeppelin!

[Steve Kroenke]

Steve R,

Please continue testing your sound deterrence system this season. I have talked with other folks who have had success with sound deterrence though it can fail just like any other.

Steve

Rob,

The ?Nightguard? system has failed I believe in several cases. I believe that Andy Troyer tried to use it to thwart great horned owl predation on his T-14s, but it did not stop the owls. I have heard that other folks tried the ?Nightguard? and it did not work consistently.

I have tried using bright lights that almost turned my colony site into daytime! The lights did not work though it made the owls very visible as they sat on the gourd crossbars or in nearby trees. So I believe that a flashing/pulsating light, which is the premise behind the ?Nightguard? system, would probably have limited owl deterrence value over time.

Now don?t knock Led Zeppelin! They rock and roll! I still like them though they are ?dinosaurs? relative to the new music stuff.

But seriously, the concept of sound deterrence has merit I believe to attack the owls at the auditory level. My preference would be some kind of ?white noise? like buzzing, running water, or something similar. Music can work as the principle is the same.

However, the sound deterrence can fail since owls also use their excellent eyesight. This is particularly true when the martin fledgling roost on exposed gourd crossbars or house perches/porches. Would loud music have some auditory fright value and still keep the owls from making that initial contact based on visible stimuli? Possibly, but numerous martins sitting side by side may just be too tempting to a hunting owls.

I just believe we need to experiment with sound deterrence over a wide geographical area and see how it works.

Steve

Emil,

I agree with you about various systems that have not been thoroughly tested. The ?Nightguard? folks are, of course, trying to sell their products! I have seen their advertisements on the Internet. Perhaps this system has worked to protect poultry/game. I don?t know. But I do know the bright lights will not stop owls.

Steve

[Jim Ray]

Just today I spotted a great horned owl brooding on an old hawk nest about 1.5 miles from my colony site.

[SonjaC]

Thanks for all of the great info on owls.

Currently, our swimming pool is fairly close to our martin colony. We make sure to run the pump/filter all night long. I know that our neighbors think we're crazy for starting this in April, but it's not because we're worried about water quality - believe me! We are pretty confident that the "white noise" effect of the pump masks the majority of our colony sounds.

We, too, have a colony in a clearing, and there are lots of owls around. In fact, we have actually lost kittens to owl predation, but (knock on wood) no martins to date.

Unfortunately, from the martin's perspective, we have just built a new house on our property and will be moving the swimming pool. So, we will have to come up with another owl/sound deterent system.

[Guest]

I wish to take just another moment to sincerely thank all of you who lay down some really good thoughts and reports from your personal experiences. Hopefully many others will take the time to soak up the goodness that is stored in the archives too. Thank you so much for the time you all have given to others.

[roblrich]

You think a Kenny Kleinpeter CD would scare the martins off, or just keep the owls away?

[abernathys]

Hey Steve--I know that our PM's love both kinds of music, Country and Western! So far the Great Horned Owl not so much! Keeping fingers crossed that the music/deterrent system will keep working, this will be the fourth year with music. Everyone have a great PM season!

Sandy