For my second purple martin season in northwest Louisiana, I am using three natural gourd types that maximize vertical/horizontal depth. I tried these gourds at my previous colony site in Tallahassee, Florida during 2004 and achieved an almost 100% occupancy in them. At my new colony site in northwest Louisiana, I tried them again in 2005 and 31 out of 36 were occupied by martins, reflecting an 86% occupancy level. These gourd designs were the most popular ones in my colony. All my gourds have round holes and are starling free. No starlings investigated or attempted to nest in any of my gourds at my previous colony in Tallahassee and none has done so in northwest Louisiana.
Here is a description of each of these gourd types and there are photos showing martins using them:
Vertically Deep Elongated Shaped ?Woodpecker? Gourd That Is Tilted Forward With Hole Cut Just Under The Neck
Woodpeckers do it vertically deeper for good reason and woodpeckers have been doing this for thousands of years. That should tell you something! Such nest cavities are more protected from predators than a shallow cavity with the entrance hole cut only an inch or less above the nest chamber. When woodpeckers excavate their nest chamber, they dig in for a few inches, depending on the diameter of the tree, and then go sharply downward in a gradually enlarging chamber until reaching the bottom. These cavities can resemble a boot in shape. Such cavities may drop vertically downward a foot. The nest site may be oval or elliptical in shape and not as large as the woodpeckers that create them. I have measured the inside dimensions of red-bellied and red-headed woodpecker and flicker cavities and these are often about four to five inches in width and five to sometimes seven inches in length. Woodpeckers sacrifice nesting chamber girth for deeper vertical depth. Purple martins nested successfully in such cavities in the past in the east and are still raising families in them out west. The martin?s short legs and sharp nails are perfect physical adaptations for climbing in and out of rustic sided cavities. Other cavity nesting birds like bluebirds, great crested flycatchers, tree swallows, titmice, woodpeckers, and others successfully nest in such environments.
You can create a somewhat similar replica of a woodpecker cavity by using more elongated shaped gourds with shorter necks. Finding suitable candidates for ?woodpecker? gourds can be difficult with most martin gourds, since many are round in shape.
This year I am using five woodpecker gourds that maximize vertical depth from the entrance hole and provide a very secure nest site for purple martins and four are occupied by martins as of March 23, 2006. However, my gourds are much larger in horizontal diameter at the gourd bottoms than a woodpecker cavity. In these gourds, the entrance is cut just below the neck on the curved contour, creating vertical depth of around eight or more inches. The foyer area around the entrance is narrow like that of a woodpecker cavity. Then the gourd is tilted forward at about a 45-degree angle so that the hole is pointing downward, producing a gradual sloping vertical descent to the bottom of the nesting chamber. This type of gourd has both vertical and horizontal depth and somewhat replicates a natural woodpecker cavity, which greatly protects any nesting birds from the reach of predators and rain inflow. When I add one of my pre-built nests of pine straw and oaks which are typically two or three inches thick, the vertical depth is reduced to about six or seven inches from the entrance hole. Martins will usually add some more oak leaves to the cavity but very little other nesting material like pine straw.
Martins have NO difficulty reaching the entrance hole because the gourd inside substrate is coarse and martins are perfectly adapted to climb such material with their short legs and strong nails. This is much better than having the nest level with the entrance hole, which will often occur in vertically shallow cavities with entrances cut only an inch or less above the bottoms.
Also, purple martins do NOT build their nest all the way to the entrance hole in ?true? vertically deep cavities. I have never seen a martin do it in my woodpecker gourds. No martin will build an eight inch thick nest to reach the top of a nine inch deep cavity so that their young are exposed to predators in the entrance hole. This would be biological/evolutionary suicide. Martins don?t do it in woodpecker cavities in saguaro cactus in Arizona and neither do other cavity nesting birds. Humans have offered vertically shallow cavities to martins and this has resulted in martins building their nests up to the entrance holes and then possibly using mud dams to reduce visibility inside and protect the eggs/young. When a martin only has an inch or less from the bottom to the entrance, then the martins have no choice but to build their nests up to the hole. If you cut a hole four inches above a gourd bottom, then the martins will usually build their nest two or three inches thick. This is not a true vertically deep cavity.
Horizontally Deep Elongated Gourd With Hole Cut In Neck And Producing 90 Degree Offset Angle Entry
This type of gourd design creates a very protective environment for purple martins because the nesting chamber and inhabitants are COMPLETELY out of view from the outside and located deep inside the gourd. Just plain horizontal depth where predators can see directly inside the hole all the way back to the gourd may create a false sense of protection. Owls can easily see these martins and scare them out of the holes right into the talons of death.
Like the woodpecker gourds, it is difficult to find gourd shapes that are suitable for horizontal suspension. Such gourds are usually more elongated than round and tend to have smaller girths. In these gourds, you cut your entrance hole in the neck so that a martin will enter and then turn at around a 90-degree angle to ?waddle? down to the vertically sloping nesting chamber. The curvature of the gourd and the way you hang it produces the amount of vertical decline realized.
I am using six horizontally deep gourds with offset holes on the necks and the depth varies from 12 to over 15 inches. Five are occupied as of March 23, 2006. Martins enter the hole and then hang a sharp turn to reach the gourd end. Plus there is a gradual vertical decline to the nesting chamber at the end of the gourd, which gives more protection to the martins. Vertical depth is modest and varies from about four to six inches. The girth at the nesting chamber portion of these gourds is from about nine to ten inches. The diameter of horizontal gourds is not as important as the horizontal depth. I have several that are about six inches in diameter but over 12 inches in length and the martins flourish in them.
Horizontally Deep ?Cliff Swallow? Gourd With Hole Cut On Neck To Produce A Funnel
Cliff swallows are perhaps the most architecturally creative hirundinids in North America and build nests that provide a secure environment for their young. These mud ?jugs? have a tunnel/funnel like entrance, which points downward and opens into the nesting chamber. If you were to give an IQ test to North American swallows, the cliff would probably score the highest!
You can create cliff swallow like nesting cavities from natural gourds without adding any kind of artificial extender. What you do is select natural gourds with long thick necks, which can be straight or curved, and a round or elongated bowl where the nesting chamber is located. Cut the neck to create about a two to two and half inch round hole to serve as the entrance. Gourd necks tend to be funnel shape whereby the inside gradually widens until reaching the bowl. Then it may drop down vertically for a few inches. These natural funnels may either protrude straight out or curve downward. Martins can easily enter the entrances and ?waddle? down the rustic interiors without slipping or sliding. There is no need to add any kind of artificial extender or perches to such entrances as Mother Nature has naturally provided the perfect portal for the martins.
I am using 34 funnel gourds and these have both straight and downward pointing funnel entrances and 22 are occupied as of March 23, 2006. These funnels vary between three to around six inches in length and the gourd bowls are between seven and 11 inches in diameter. This is producing excellent horizontal depth from around 12 to over 15 inches and good vertical descent as much as six inches to the nesting chamber.
Funnel gourds create a nesting chamber that is significantly protected from the watching eyes of owls and rain soakings. The downward sloping funnels provide the best security for the martins.
However, on a number of my funnel gourds, the neck area was too short after cutting the end. I had a round hole and a way too short funnel portal. So on these types, I attached PVC joint pipe connectors, both straight and angled, to extend the neck area out and create a tunnel which transitions into a more funnel like opening. I attached the connectors with adhesive and aluminum strips used like ?band aids?. These PVC connectors are used to join two inch diameter pipes and the hole produced is around two and half inches. The connectors are about three or four inches in length. The angled connectors create about a 45 degree turn. Since PVC is plastic and slick, martins may have a hard time entering and clinging to such a substrate. So I roughed up the inside of each connector and then smeared adhesive all over the area where martins would climb on to create a rippled surface. The adhesive was the same I used to attach the connectors to the gourds. Then I mixed a little dirt in the adhesive and this surface provided the traction for martins to easily climb on. To make sure martins could easily enter these PVC extenders, I also attached ?oval? shaped wire perches to the bottom of each of the PVC extenders using No. 10 plastic coated copper wire. I drilled two small holes about an inch inside at the bottom of the PVC connector and inserted the wires through them and bent the wire ends. This created a perch which protrudes about three inches out from the bottom of the PVC extender. Martins can easily sit on these wire perches and enter the holes.
I am also using 34 Troyer plastic horizontal gourds which are similar to my funnels. I am looking forward to seeing if there will be a difference in occupancy levels between the two designs.
I would encourage other folks to try these gourds and see how martins respond to them. I have had a tremendous response to them! However, I use only round holes for such gourds and round holes may be more suited for such cavities. Srehs may be more appropriate for vertically shallow cavities as martins may have a difficult time exiting these restrictive entrances from such nesting chambers. But folks may still be able to use srehs with some creative hole positioning and inside porches.
Steve Kroenke
