How Great Horned And Barred Owls Find Purple Martin Colonies

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Steve Kroenke
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How Great Horned And Barred Owls Find Purple Martin Colonies

Postby Steve Kroenke » Wed Aug 21, 2019 12:12 pm

How Great Horned And Barred Owls Find Purple Martin Colonies

Have you ever wondered how those ferocious night hunters, the great horned and barred owls find your purple martin colony? It’s not hard for them and the martins make it easy! Owls have two powerful weapons for finding “your” martins.

It is a matter of sound and sight and the owls excel in both categories during the darkness. 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 or the calls and night noises of martins residing inside their nests or martins vocalizing while perched outside on gourd racks or houses during the darkness. The owl tracks the sounds like a wolf on the trail of a deer. The great horned 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. So sound is one key weapon that owls use to find martin colonies.

The other attribute is the sight weapon which complements the owl’s incredible hearing ability. 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. Martins roosting outside on gourd racks and house porches are easily seen by owls and dawn singing males clearly reveal their presence not only by their vocalizations but their physical profile.

Purple Martins Advertise Their Location In The Darkness And The Owls Are Listening And Watching

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 darkness and this can mean death 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. Both male and female martins may vocalize inside their nests. I have heard these calls 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 previous Florida super colony. I was amazed at the amount of singing/chatter by the martins. One male would gurgle and then another would answer. And these were relatively 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 ASY males make these calls to attract SY females. The males start their vocalizations at around 4:00 am and may 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 may leave to continue the singing in the sky above the colony. Other males remain at the colony and dawn sing on gourd racks and houses or from the entrance of their nests.

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 in aluminum houses and the knocking noises are audible. Large young may emit 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.

At roosting time, particularly at large martin colonies, many times a number of migrants or other non-resident martins arrive to sleep. This creates chaos for the colony as the residents fight and try to keep these new arrivals OUT of their nests! When these other martins force their way into permanent residents’ nests, fights break out accompanied by loud vocalizations which can continue into the night. These “sleepers” will “plant” themselves on a porch in front of an active nest sometimes and try to roost there. The nest owners will often vocalize loudly at them. Others just try to roost out in the open on house porches. All this fighting and loud vocalizations can be easily heard by owls and they may eventually visit.

These various martin vocalizations and other sounds are easily detected by hunting owls. The larger the martin colony the greater the volume of these vocalizations and the sound waves spread in the darkness to the ears of listening owls. It is just a matter of time before an owl may fly over to the martin colony to check out the potential food source.

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 those martins. Some purple martins do NOT stay still inside their nests during the darkness, particularly early in the mornings. 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 stick their heads out of the entrances and vocalize while others may 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.

And when martins unwisely roost out in the open on gourd racks and house porches, owls don’t even need to hear the vocalizations initially and may just use their night vision to see the martins. At large martin colonies migrating martins may “stopover” to roost and if they can’t find an empty cavity, the martins may end up roosting on house porches or even inside some gourd rack support rods. Big mistake when owls are hunting nearby.

These larger martin colonies tend to have a major problem when many martin fledglings in particular return back in the evenings to roost. The houses and gourd racks may be “covered” with the fledglings. These situations are most attractive to owls which readily attack and eat the martin fledglings.

Purple martins by their behavior and vocalizations just prior to roosting and continuing during the night and early morning darkness are the primary reasons why great horned and barred owls find martin colonies in the first place. Martins advertise the location and expose themselves to owl predation. If martins kept quiet during the night and early morning darkness, stayed inside their nests until the first morning light, and did not roost outside on the gourd racks/houses, then owl predation would probably never be a problem in most situations. The owls would never hear or see the martins at their colony! At times martins can be their “worst enemy” by placing themselves in jeopardy by their own actions! It seems martins have a “death wish”! But we landlords enjoy the many behaviors and vocalizations and, unfortunately, so do the owls!
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G Saner
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Martin Colony History: Fort Worth, TX (1967-1976), The Colony, TX (1981-1985), Carrollton, TX (1986-2013), Kerrville, TX (2015-present).

Two SuperGourd poles (12 gourds on each) at River Point Assisted Living Center.

Re: How Great Horned And Barred Owls Find Purple Martin Colonies

Postby G Saner » Wed Aug 21, 2019 4:43 pm

Hello Steve,

I know you use netting to protect your colony against snakes but do you use anything to protect your super colony against owls? Gary
G Saner

Steve Kroenke
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Re: How Great Horned And Barred Owls Find Purple Martin Colonies

Postby Steve Kroenke » Wed Aug 21, 2019 5:57 pm

I have studied owl predation on my various martin colonies in Florida and now in Louisiana for many years. In Florida, I dealt only with barred owls and in Louisiana great horned owls. Based on what I observed, barred owls have been more destructive than great horned owls. Barred owls are slightly smaller and mainly nest in cavities. So these owls are skilled at clinging to tree sides and appear to be more acrobatic around a gourd rack or house than the larger great horned owl.

What I have done in Louisiana with my current colony is to make sure NO martins roost out in the open. I always “put my martins to bed” so I patrol around the colony and look for any martin that may be trying to roost on a house/gourd porch or inside a gourd rack. If I see one, I chase that martin off. When huge numbers of martin fledglings are coming back to roost in the evenings, I do the same. I don’t like to chase them off, but either I can do it gently or the great horned owls will be more than happy to do it for me and slaughter the fledglings in the process. (For 2019 we had no owl predation that I observed so our martins could roost in peace and I didn’t have to chase the martins off.)

I also get up early in the mornings at around 4:00 am and go on “owl patrol”. This is particularly important during the dawn singing time when the male martins are basically “calling the owls in”! As long as I am out in my martin colony and walking around the area, the great horned owls will not swoop in.

Great horned owls in our area “hunt like hawks” and catch VISIBLE martins sitting on porches/perches and roosting outside. So far, I have not seen these owls hanging on gourds/houses like the barred owls. Barred owls, from what I saw in Florida, are better at actually attacking gourds/houses and clinging to them to pull out or flush out martins. Barred owls will also attack visible martins, too.

I don’t plan to enclose any of my gourd racks/houses in cages. This approach would probably not stop our great horned owls from trying to capture visible martins sitting on porches or gourd racks inside the cage. The owls would just fly up to the cage and possibly perch on top or cling to it and terrorize the martins into trying to get out. Martins could be injured trying to fly through the wire and the owls could still grab them. We have so many martin fledglings trying to roost in our colonies that many would most likely try to roost all over the cages, too. These would still be vulnerable to owl predation.

In the past at my last Florida martin colony, I had success my last year with using a sound deterrence method to mask the nocturnal vocalizations of the martins. I started this BEFORE any actual barred owl predation occurred and it appeared to work. I played loud hard rock music using an outdoor speaker from dusk to dawn throughout the season. The barred owls never predated my colony that I could determine. However, this was used only for one season and may not continue to work.

Another possibility for deterring barred owls would be to use great horned owl decoys on tall poles around your colony. Great horned owls are enemies of barred owls and could kill and eat one. You could place realistic great horned owls decoys on poles AFTER your martins go to roost and see if the decoys created any fright deterrence for barred owls that were attacking your colony. You would need to move the decoy poles around the area. I tried this approach with my current colony one year after great horned owls were attacking martin fledglings roosting out in the open. It actually worked for a while but the owls eventually “got used to them”! But might be more effective with barred owls.
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Chris B
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Re: How Great Horned And Barred Owls Find Purple Martin Colonies

Postby Chris B » Thu Aug 22, 2019 8:09 pm

Darn raptors (or whatever the claws of death from above are called) are no fun either.

Do lights in the general area help? I know they lights where they roost at. Mine had burned out and I will probably put them back up for next season. Security lights around buildings in the area.
2014 8 gourds, 3 pairs nested. Ended w/ 24 total
2015 24 gourds, 22 nests. Lotsa birds!
2016 24 gourds and good activity.
2017 32 SREH gourds. Great activity.
2018 40 SREH gourds. Good finish despite big storm damage. No more dangling gourds.
2019 56+ SREH gourds, all on 3/8 rods.

Steve Kroenke
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Re: How Great Horned And Barred Owls Find Purple Martin Colonies

Postby Steve Kroenke » Fri Aug 23, 2019 6:00 am

In the past I tried using various bright lights to discourage barred owls from raiding my Florida martin colonies and the lights did nothing to prevent attacks. Currently, I have a security light that illuminates much of my martin colony and the light does not stop any great horned owl from swooping in to grab martins.

The lights may reveal any owl perched on a gourd rack or house top and show an owl flying through your martin colony or actually attacking a martin.

I believe I read where some landlords have used motion sensors to "sense" an owl approaching their martin colony and then a bright light comes on suddenly that may startle an owl. According to the landlords, this action can discourage an owl from attacking. But I've never tried anything like that.
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Donnie Hurdt MN
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Re: How Great Horned And Barred Owls Find Purple Martin Colonies

Postby Donnie Hurdt MN » Sun Aug 25, 2019 6:10 pm

Hi Steve, Great article on Owl predication. For the past two years or so we have a pair of Barred Owls nesting in our yard. They have become quite interesting to watch and they have become quite interested in watching me doing things around the yard. It is amazing how tame they have become, as I have never made any aggressive motions to scare them away. They will pick up small critters that I have shot in the yard and when I mow the lawn they will fly down and pick up frogs that I scare up even landing right beside the riding mower to catch prey. I can get quite close to them and they will mostly ignore me but when my wife or someone else is with me they are more skittish.
I still don't have any martins nesting here and most likely wont as long as the owls are here these owls are neat. :)
PMCA member and Martin fanatic....
2011 A pair of subbies fledged three young but none returned in 2012 :-(
2015 One Pair of subbies came and stayed a few nits but got chased away by Bluebirds and Tree swallows. :-(
2017 0ne pair of subbies nested and fledged 4 young
2018 Tree Swallows AGAIN chased away any martins that wanted to nest :evil:

Steve Kroenke
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Re: How Great Horned And Barred Owls Find Purple Martin Colonies

Postby Steve Kroenke » Sun Aug 25, 2019 7:50 pm

Hey Donnie,

Barred owls and purple martins don't "mix very well", but the owls are interesting raptors!

When I lived in Tallahassee, Florida, my last supervisor had a goldfish pond in her backyard. Well a barred owl started "fishing" and almost wiped out her fish! She had to put fencing over the top of the pond to keep the owl from catching her fish! I have talked with other people who have observed barred owls "fishing".

There is a city park near the office building where I worked in Tallahassee. A pair of barred owls nested for several years in a large cavity in a magnolia tree. Sometimes I would see their nestlings peeking out of the cavity when I walked through the park.

But barred owls decimated several of my martin colonies in Florida.

Thank you for sharing your observations of "your" barred owls!
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daveh
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Re: How Great Horned And Barred Owls Find Purple Martin Colonies

Postby daveh » Mon Aug 26, 2019 9:11 am

Steve, I have motion detector lights on my poles. They did nothing to the barred owls but gave them more light to hunt.

Dave
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Steve Kroenke
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Re: How Great Horned And Barred Owls Find Purple Martin Colonies

Postby Steve Kroenke » Mon Aug 26, 2019 10:55 am

Dave,

I agree that lights, probably of any kind, will have little impact on deterring barred or great horned owls. I had bright lights shinning on several of my martin colonies in Florida and the owls would even perch on the gourd racks with lights shinning on them.

I read on Facebook where a landlord uses a motion sensor that would come on when a great horned owl approached his martin and then activates a bright light in the owl's eyes. The landlord said this method did keep the owl from attacking his martin colony. So such a method may work for some owls.

Owl predation can vary in intensity. Some owls seem to continue attacking no matter what we do while other owls may not be as aggressive or persistent and can be discouraged easily. All the barred owls that attacked my Florida martin colonies were not easily discouraged! The great horned owls around our Louisiana colonies are persistent and aggressive, too.

With barred owls, perhaps try using some realistic great horned owl decoys on tall poles around the perimeter of your martin colony next year. Usually such approaches don't work for long but it might help. Great horned owls are deadly enemies of barred owls and can kill and eat them. Several seasons ago I placed three decoy great horned owls with "rotating heads" on poles around my martin colony. I was hoping that these "fake" great horned owls may offer some territorial deterrence to the owls which were attacking martin fledglings coming back to roost. Well the approach worked for about a week and then failed. Maybe with barred owls the approach could possibly be more effective as barred owls KNOW great horned owls are killers! Just something to consider.

I had success with sound deterrence using loud rock music played from dusk to dawn BEFORE any owl predation occurred at my last Florida martin colony. The music apparently masked the nocturnal vocalizations/sounds of the martins and the barred owls never "found" my colony. However, I only used this approach a few times in Florida so I don't know if it would have lasting success.

I have tried other approaches like scarecrows and these may work for a short time and then they all failed.

The only way I can keep the great horned owls OUT of my current martin colony and from catching visible martins is to chase off martins roosting/perching on the houses/gourd racks. And then patrolling around my martin colony early in the mornings when martins are coming out and perching on houses/gourd racks in the darkness. My presence keeps the owls from attacking.

Large owls are apex avian predators of the night. What we need is something that frightens the owls and keeps them AWAY from our martin colonies in the first place or something that "hides" our colonies from the eyes and ears of the owls. I wonder if a "fake" bald or golden eagle on a pole near our martin colonies would work! What about a human robot that walked around our colonies all night long!
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