Rat Snake Predation
Steve Kroenke, DNASRK28@aol.com, Tallahassee, Florida
Rat snakes are significant predators of purple martins and there are a number of different species. These snakes are widely distributed throughout the United States with the largest concentrations in the Deep South. The gray rat snake is the dominant species in North Florida where I live and is often called the "white oak snake". My yard is infested with them. They often stretch out on exposed mimosa limbs near my bird feeders and wait for an unsuspecting bird to land on them. When this happens, the snake quickly coils around its prey and suffocates it. Some days I remove several large rat snakes from this area and release them away from my feeders. We also have the beautiful corn snake, known as the red rat snake, and the yellow rat snake. The black rat snake lives further North.
All these snakes are powerful constrictors, can be quite long, and are somewhat like miniature pythons/boas. These snakes are designed to suffocate their prey with strong, unyielding constrictions. They coil around their victim and each time the prey exhales, the coil is tightened. Eventually the prey is suffocated and then swallowed, usually head first. Though their name implies "rat" hunter, these snakes are formidable hunters of both cavity and non-cavity nesting birds. It makes no difference if the prey has fur or feathers--it is warm blooded and that is what counts.
Rat snakes raid numerous purple martin colonies each year and many of their depredations go unnoticed until it is too late. These snakes often hunt at night and this significantly reduces the chances that a martin landlord would see one crawling near his/her colony. Unfortunately the vast majority of purple martin house/gourd poles offer no protection from these predators. Many landlords do not believe that these snakes are living in well-maintained yards or in suburbia, or that they can climb metal poles. I once "talked myself blue in the face" with a lady who finally said, "Why young man, no snake can climb these metal poles!" She actually scolded me! These landlords are mistaken, as rat snakes are very common, particularly in the Deep South, and they CAN easily climb metal poles. All purple martin landlords need to beware of the "belly crawlers" and how these formidable predators find and raid martin colonies.
HOW DO RAT SNAKES FIND AND RAID PURPLE MARTIN COLONIES
They donít need sight nor do they need sound. They donít need great speed. They donít need a "hunterís moon" in the dead of night and they can find their way in total darkness. The rat snake has a "secret" biological weapon that would rival the most sophisticated radar tracking system known to mankind. All they need is a few molecules of warm-blooded "scent" and that will be enough. Their prey can be as little as five feet off the ground in a bluebird house to 30 or more feet high up a tree in a open birdís nest. And nothing is more inviting and tempting than a purple martin house or gourd cluster filled with adult and baby purple martins. Such a large concentration of available prey fills the air with its "scent" that disburses widely into nearby thickets, overgrown lawns, trees - places where a rat snake may be crawling or hiding and "sniffing" the air. Rat snakes are basically scaly "blood hounds". They have highly developed, very sensitive sensors that allow these snakes to "sniff" the air with their tongues for prey. Once these snakes detect the "scent" of a possible meal, the hunt begins and their sensors guide them to their victim(s). They are relentless in their silent pursuit and follow the "scent" like a wolf on the trail of a deer.
A martin colony filled with adult and young birds is a feeding bonanza to any hungry rat snake. The martins, sleeping in their houses/gourds, are totally unaware of the slithering horror that is crawling toward them. Once the snake reaches the base of the martin house pole, the snake begins its ascent. By now the air is thick with martin "scent" and the snakeís tongue flickers in and out, "tasting" its forthcoming meal. Slowly, inexorably, the snake propels itself upward in a corkscrew maneuver, using its powerful coils to constrict itself forward up the pole. The martins are totally oblivious to the approaching danger as the snake makes no sound nor produces vibrations that could frighten the unsuspecting martins as they sleep. A suffocating death is now just minutes away. When the snake reaches an entrance hole to a gourd/house compartment, its head enters first followed by its body, which slides into the nest, filling the gourd/house compartment, and blocking the entrance hole. Adult and young martins alike are caught in the snakeís coils, suffocated, and devoured; small, unfeathered young may just be swallowed alive. The chances of any adult martin escaping out the hole are slim unless the snake is small and does not completely block the entrance. Also, the snakeís body is highly sensitive to the touch of potential prey and any martin that brushes against the snake is quickly snared in the snakeís coils. After the snake has consumed the martins in that nest, the snake may coil up and remain there for several days to digest its meal. Other times, the snake, if still hungry, may then continue to follow the martin "scent" and raid other nests in a house or gourd cluster. Some snakes, after eating their fill, leave the house/gourd cluster and climb down the pole.
BEHAVIOR OF MARTINS WHEN RAT SNAKE IS VISIBLE ON/IN HOUSE/GOURD CLUSTER
Purple martins will "let you know" when a snake is on the house or gourd cluster crossbar or if the martins see the snake inside a house compartment/gourd. The martins appear agitated and are reluctant to land on the house/gourds. They may hover around the house/gourds. Sometimes they will land on the martin house roof or gourd crossbars. If your martins are behaving in such a manner, then there may be a snake either on the outside or inside the house/gourds.
HOW DO RAT SNAKES CLIMB; UNDERSTANDING SNAKE PHYSIOLOGY
Rat snakes donít need hands, claws, arms, a ladder or spiked boots. They are superbly designed to employ their unique belly scales and powerful body movements to climb a variety of surfaces. Their bellies seem to "stick" to rough surfaces like "biological hooks", momentarily holding the snakes in place, and then allowing them to slowly climb forward without falling backwards or downwards. I have seen these snakes climb straight up cedar siding and brick walls of houses. Large diameter trees, living or dead, and utility poles are easily climbed, much in the same manner as flat, rough surfaces like wood or brick walls. I have also seen these snakes climb small diameter objects like wooden and metal poles. When climbing small diameter poles, the rat snake tends to coil around it, then slowly constricts itself upward while maintaining enough pressure on the pole to keep from sliding back down. The snake slowly meanders up the pole. The rat snakeís combination of "adhesive like" belly scales and powerful coiling abilities allow the snake to climb almost anything it seems.
HOW TO REDUCE THE CHANCES OF SUCCESSFUL RAT SNAKE PREDATION
There are a few grounds keeping tips that landlords can employ to at least make their sites "less inviting" to snakes. Snakes like cover where they can hide and look for prey. Always keep the grass around the martin pole set ups cut short and maintain an open area. Keep your houses/gourd clusters away from thickets and brush piles. Donít plant flowerbeds at the base of the martin house poles or allow vines to climb the poles.
Rat snakes may be less inclined to crawl a long distance across an open lawn since such a move exposes them to their night enemies such as barred and great horned owls, and day enemies like red shouldered and red tailed hawks. In North Florida, where I live, red shouldered hawks are a main predator of rat snakes, and I have seen many rat snakes in the beaks and talons of these hawks. So various grounds keeping techniques may help reduce rat snake predation by making the immediate area around your colony less attractive to snakes.
Additionally, you may want to check the base of your martin house/gourd cluster poles during the early morning, evening, and at night to see if any rat snake is trying to climb the poles. I have seen on a number of occasions gray and red rat snakes either at the base of my martin pole set ups or crawling toward them during the evening and night hours. This season I watched (using a flash light) a 3 feet long corn snake (red rat snake) late one night unsuccessfully try to climb one of my gourd cluster poles that was protected with a snake guard.
Rat snake predation has been a significant problem for ALL hole nesting birds that have nested in my bird houses. Before I actively intervened and installed various pole guards, I lost numerous bluebirds, Carolina wrens, chickadees, crested flycatchers, titmice, red-bellied woodpeckers, and purple martins to both gray and red rat snakes. Also, I am amazed at the number of non-cavity nesting birds, such as cardinals, towhees, brown thrashers, mocking birds, ground doves, etc., that loose their eggs/young to rat snakes in my yard.
POSSIBLE RAT SNAKE GUARDS
So what types of guards can a landlord use to eliminate or minimize the chances of rat snake predation on his/her purple martin colony? There are a variety of systems and we martin landlords need to keep thinking of possibilities and experimenting and sharing our ideas with each other. Remember: no system is totally fool proof and some huge rat snakes may defeat you no matter what you do. Here are some ideas.
Greased Pole Method (Not Recommended)
This is a very, very nasty method of deterring rat snakes and can work with metal poles if you apply GENEROUS amounts of grease to the bottom of a bird house pole and KEEP it moist. Many years ago I used this method. I applied enough white lithium grease to provide about 1 inch thickness around the pole and about 4 feet up the pole from the ground. I went through can after can of this nasty grease. Numerous gray rat snakes would try to climb my martin house/gourd poles, but they never got more than a foot up. I found more than one totally greased rat snake at the base of my martin house poles. Some of the snakes were so determined to climb the pole that they had taken off most of the grease at the bottom of the pole! These snakes were covered from head to tail in grease. However, I do not recommend this method for 2 major reasons: (1) it is just plain nasty and will get all over you and anything else touches it; plus it may be harmful to the rat snake or any predator that may eat the "greased" snake; and (2) you MUST apply LARGE amounts of grease and KEEP it greased through out the season. If you allow the grease to "dry out" or you do not apply enough to completely coat the metal pole, then a determined rat snake can sometimes climb through it. I had several cases of this and I could see the horrifying corkscrew grease trail all the way up my gourd poles.
Inverted Bucket/Cone/Other Pole Baffles
These guards prevent the rat snake from ascending the pole and stop the snake a few feet up the pole. A five or ten gallon inverted bucket attached to the pole about four feet from the ground provides a good rat snake barrier. Most rat snakes would crawl up into the bucket and would be stopped. However, huge rat snakes may be long enough to lift themselves up in front of the bottom of the inverted bucket and then wrap around or go over it. Kent Justus recently reported on the Forum of huge snakes that appear to have defeated this guard at his new martin colony. You must make sure there are no openings between the hole in the bucketís bottom and the house pole that is inserted through this hole. Even a small space may allow a rat snake to squeeze through the opening and continue its journey upward. Also, you could coat the outer surface of the bucket with Vaseline to create a slick surface for possible added protection.
You can build your own cone shaped baffle out of aluminum/metal sheeting that looks like a "bell bottom" and functions similarly to the inverted bucket. This cone could slope down 2 feet or more with a diameter of 2 or more feet. Like the inverted bucket approach, the rat snake would crawl up into the cone and be stopped there. Again, a coating of Vaseline on the cone may provide some additional protection should a huge rat snake manage to lift itself up to reach the outer surface of the cone.
This is a cylinder method. You can slip a piece of plastic PVC pipe that is at least 6 inches in diameter and about 4 to 5 feet in length on the bottom portion of the martin house/gourd cluster pole. The pipe should be pushed a few inches into the ground so no rat snake could crawl under the pipe and then reach the pole. You can also create a stove pipe out of aluminum sheeting, which is similar in principle to the PVC pipe approach. This barrier prevents the rat snake from coming in contact with the martin house/gourd cluster pole. To enhance the slickness of either the PVC pipe or stove pipe, you can coat both with Vaseline. This may prevent the rat snake from successfully coiling around the PVC pipe or stove pipe, holding tight, and then proceeding to constrict upwards. A metal or aluminum stove pipe may eventually become weathered thereby producing a roughened surface that could allow a rat snake to climb it.
Use an adjustable cylinder pole guard that combines both a slick aluminum surface and wobbly motion to thwart both rat snakes and raccoons . To enhance the aluminumís slickness, you could coat a layer of Vaseline on the cylinder to provide some possible added protection. Aluminum, over a period of time, may become weathered with a somewhat roughened surface. This may allow a big rat snake to climb or more easily coil around the cylinder and constrict upwards.
Flat disk (With Or Without Downward Pointing Border Fence)
Rather than a cone or bucket, you may consider a flat disk (not necessarily round and could be square) approach. Such a disk would need to be around 3 feet in diameter to really stop a huge rat snake, though a disk 2 feet in diameter would probably deter many snakes. This disk could be metal or wood. You could also add a border fence around the perimeter of the disk that points downward. This downward pointing fence would add some additional protection and may keep any super long rat snake from reaching around the disk. This fence could be metal/aluminum sheeting, wood or some other material and could protrude down anywhere from 6 inches to a foot or more.
Plastic Skirt Method (A Possibility That Works For Me)
I call this guard the plastic skirt. This method is rather simple and is based on "giving the rat snake nothing concrete to climb or coil around". If the snake is confronted with multiple layers of loose, slick, wobbly plastic, then the snake has a difficult time employing its superb climbing skills. I have used this method for about 10 years so far and not a single bird house has been raided by rat snakes and they have tried on numerous occasions. This method has worked for me, but is definitely not a sure thing - in fact, nothing is a sure thing when dealing with rat snakes. One observer reported that a martin landlord used this approach and rat snakes still managed to climb the pole.
I use relatively thick black agricultural plastic sheeting that can be purchased at any home improvement store. You'll also need a pair of scissors, some wire, a yard stick, and if you want to attach the plastic to wooden poles with nails, nails and a hammer. Cut a piece of plastic sheeting about 5 feet by 5 feet square; this can be larger if so desired. At about 5 feet from the ground, began wrapping about 6 inches to a foot of the plastic top tightly around the pole, leaving the remaining 4 feet or so of plastic loose. The bottom of the plastic should be about 6 inches from the ground. Take some the wire and wrap it tightly around the top of the plastic sheeting to hold the plastic firmly to the pole. At this point the plastic guard should somewhat resemble a skirt or "bell bottom". The plastic guard is narrow toward the top and gradually flares out toward the bottom. Make sure the bottom portion is loose and flares out.
The plastic guard works in many cases because the rat snake has a difficult time climbing or coiling around a slick, loose, wobbly plastic skirt--there is nothing solid for the snake to cling to. Also, the rat snake will often try to ascend the pole that is protected by wrapped plastic. The snake will be squeezed tighter and tighter while trying to climb the pole inside the plastic skirt and being compressed against the pole by the multiple layers of gradually tightening plastic.
Plastic often deteriorates after prolonged exposure to the sun and the elements. This weathering may reduce the plasticís slickness and flexibility, thereby giving a rat snake a chance to climb on or around the plastic. Though some of my plastic skirt guards have lasted several years, I usually replace mine each year. I, now, coat the outside of the plastic skirt with Vaseline to really enhance the slickness and flexibility of the plastic sheeting. I have also provided a Vaseline coating to the bottom portion of my gourd cluster poles up into the plastic skirt to not only make it slick for rat snakes (another barrier for them) but also deter ants. I keep recoating the Vaseline several times during the season to reduce the chances of it drying out.
I have observed several rat snakes try to climb my martin gourd poles that were protected with plastic skirt guards. In each case, the snake was unable to navigate around the plastic or the snake climbed up the pole inside the plastic skirt and then was forced down due to the gradual compression of the plastic against the snakeís body. This season I watched a 3 foot long corn snake try and try to climb around and through a plastic skirt guard that also had a good coating of Vaseline. The bottom portion of the pole was coated with Vaseline, too. The snake gave up after unsuccessfully trying to climb the Vaseline coated pole inside the plastic skirt. The snake also tried to "lift itself up" from the ground, and tried to climb or coil around the wobbly, flared plastic. The snake was unable to accomplish this maneuver, too.
FOR MAXIMUM PROTECTION, USE A COMBINATION OF GUARDS
If one system fails, then it makes sense to have a back up. An inverted bucket and a plastic skirt combination would be a formidable barrier to any rat snake. First, the snake would have to navigate around the wobbly, slick plastic. Somehow, the snake would have to cling, coil, and climb up and through layers of slick, loose, wobbly plastic. If the snake succeeded, then it would crawl up into the inverted bucket. Such multiple barriers may be the best approach in defeating determined rat snakes.
DONíT LET YOUR MARTINS BECOME VICTIMS OF RAT SNAKES
No responsible purple martin landlord should erect a martin house/gourd cluster without attaching a pole guard to eliminate or minimize rat snake predation. Remember: these snakes are everywhere and very common in the Deep South. They CAN easily climb both wooden and metal poles. They donít need sight or sound to find your martin colony. All they need is the martinís "scent" and their superb biological sensors will guide them right to your martin colony. If you did not have a snake guard on your house/gourd cluster pole this year, be sure to start planning to add one for the next martin season. It will only be a "matter of time" before a "belly crawler" finds your colony - think about that. Think about that rat snake entering a martin nest during the dead of night and what happens to the martins. Protect your colony.