Understanding How Owls Raid Purple Martin Gourds And Houses
From: Steve Kroenke, Tallahassee, Florida
Date: 2/2/02
Time: 10:31:37 AM
Comments
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 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 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 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 Hell! 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.
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 plentiful and seem to be increasing in population and expanding their nesting range. Both species have become urbanized and even nest in city parks. 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. 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. Owls have some of the most sensitive hearing abilities in the animal kingdom and can detect a variety of sounds from a squeaking mouse in deep grass to the night noises of purple martins sleeping "safely" in their nests. Owls have what I call is an "auditory global positioning system". The eyes of the owls are super sensitive, too, and may be as much as 100 times more efficient than humans under dark conditions. At night, owls can see small animals scurrying along the forest floor, the shapes of roosting birds, and the movement of martins in those small nest cubicles 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. One year in mid-March I stayed up all night chasing barred owls away from my colony. I was amazed at the amount of singing by several of 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. Yes, within minutes a huge barred owl flew in to investigate. 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.
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 live, 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 down in my 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. 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. 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.
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 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 and 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 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 6"x 6" compartments with nest holes only one inch above the floor. The martins in such houses are highly vulnerable. 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.
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 an occasional scratch mark around entrance hole. You may see material hanging out of the nests. Again, violent owl attacks may twist the gourd on it 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. 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 and not any Accipiter hawk. 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. 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 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.
Minimizing Owl Predation On Gourds And Houses: What Didn’t Work For Me
There were a few owl deterrent techniques that did NOT work for me. I am not saying they wouldn’t work for you. I tried bright lights, scarecrows, playing hard rock music (Led Zeppelin), huge natural gourds (some 12 inches in diameter), and larger house compartments. I even tried placing scarecrows on tall poles (over 12 feet) next to the gourd clusters, and I could still see the barred owls sitting on the gourd clusters not more than a few feet from the scarecrow! I tried using cardboard silhouettes of both barred and great horned owls placed on poles near my colony in an attempt to create a possible territorial deterrent; different owl species don’t get along. But my replicas failed. Some of these techniques like lights, scarecrows, and loud music may work initially and I saw that happen. But they didn’t last in my cases.
What May Work Or Least Minimize Owl Predation
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. However, 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 have been using such guards for some time now, barred owls continue 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 seem to 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.
For houses, double nest-chambered compartments provide good protection for the babies and incubating/brooding female martins as the actual nest site is AWAY from the front panel entrance hole. Such females tend to remain tight on their eggs and babies even if owls are creating an outside disturbance. Just having a large compartment without a SEPARATE nest chamber and with an entrance hole only inch above the floor is NO guarantee for protection, particularly the baby martins. 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. 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 provides 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.
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 doors stop 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.
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. In the past, martins nested for thousands of years as single pairs or in isolated groups in abandoned, deep woodpecker holes. Such a nesting arrangement is far less vulnerable to owl predation.
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 into 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 time before a huge barred or great horned owl "hears" your martins at night and comes to pay a deadly visit.
Steve Kroenke, Tallahassee, Florida
