Revised February 2013
Box Mounting Method
guard' for predator protection
No Ladders -- No Trees
Story and photos by Dr. Roger Strand
Fifty years ago I was up there too -- balancing on a shaky extension ladder checking my tree-mounted wood duck nest boxes. Over the years since then I’ve made about every mistake possible while managing wood ducks and boxes. My biggest mistake was hanging the boxes on trees, and as high as I could. Not good. In time, the talented squirrels, mink, and raccoons on my farm figured out that those odd rectangular things were either great nest sites (squirrels) or food shelves (mink and raccoons.) There is a better way for both humans and hens, and it does not involve either ladders or the wrapping of trees.
Background: Wood duck hens evolved to nest in natural tree cavities. A recent study showed that only about 20% of such nests successfully hatched. Failed nests and dead hens were mostly due to raccoon predation. While it seems natural to mount nest boxes on a tree, it is difficult to protect them from climbing predators. On the other hand, it’s simple to exclude these predators if the box is mounted on a pole and protected with an effective predator guard. Hens readily accept these set-ups, giving them a great chance to be successful. Studies have shown that hens actually prefer low-mounted boxes. Higher is NOT better, only more dangerous and difficult.
The Method: The Wood Duck Society (WDS) has endorsed a Best Practices method of box mounting. It involves bolting a side-opening box to a pole, with the hole just six feet from the ground. A metal cone predator guard is placed below it. The box has a side-opening door, which allows walk up monitoring. One good plan for building such a box was designed by the late conservationist, Don Helmeke. Both the box plan and the details of the Best Practices method can be downloaded from the 'Best Practices' link at the top of this page. The photos at the bottom of this page show the method in action on jump day.
Material Sources: Cedar nest box kits are available from the Minnesota Waterfowl Association (MWA) at www.mnwaterfowl.com Cone predator guards and supporting brackets may be purchased through MWA’s Prairie Pothole chapter website at www.prairiepotholeday.com
History and Cone Rationale: No predator guard is 100% effective, but this one comes very close. In Northern Minnesota, bears remain unimpressed, and avian predators are, of course, not deterred. Cone guards are widely recognized as the best deterrent against egg-eating rat snakes and their kin. Bellrose and Holm, in their classic text, Ecology and Management of the Wood Duck, stated: “When constructed to the proper dimensions and snugly fitted, cone shields provide the best available protection against pole-climbing predators. On my 100 box unit in Minnesota, loaded with raccoons, mink, and squirrels, I shifted in desperation to this technique over 30 years ago. The mammalian predation rate plummeted to zero (really) and it has stayed there.
A Picture says a thousand words; the reason for a 'cone guard' This picture was not staged. This raccoon took up residence over the winter. Even though a nesting wood duck was not involved, it demonstrates the ease in which four legged predators can gain access to a nest box if the box installation has no cone guard. During nesting season, a raccoon is skilled enough to climb onto a nest box ( a box without a cone guard) and kill a hen and/or feast on her eggs.
Photo by Jeffrey Bahls.
Constructing a cone guard:With a minimun of instruction, teenagers at the MWA's Woodie Camp make it look easy--and it is. Dangling PVC pipe guards may deter swimming predators on the over-water poles, but have been unreliable for me on land based, walk up poles. Squirrels have usually been the first to figure out that they can scramble up a PVC pipe after it loses its initial sheen. Over-water poles eliminate the squirrel, but not the need to deal with boats, waders, changing water levels, and ice-out pole-bending.
The mischievous raccoon at it again
A tree trunk wrapped with metal is not enough protection for your hen wood duck and her clutch. A crafty raccoon can still navigate installations similar to this and compromise the nest box.
Avoiding all nest box installations on trees is still the best option to prevent four legged predation. Our 'Best Practices' method for nest box installation, on this page, is strongly suggested.
Photo compliments of Ron Bice
Poles and construction details: Eight-foot long, 4"x4" posts, treated for ground contact, work well and are readily available. Using a post hole digger, carve a hole two feet deep. Drop the post in the hole, then surround the post with dirt and tamp firmly. You now have a “tree” right where you want it. Bolt the box to the pole so the entrance hole is six feet from the ground. If discarded stop sign poles are available from the local highway department, pole placement is even easier and can be done in wet areas. For metal poles, bolt two 40 degree angled support brackets to the pole below the box, then wrap a three foot diameter sheet metal cone guard over them. The skirt edge of the cone should be at least three feet from the ground. A Vise-Grip pliers will hold the overlapped edges of the cone in position. Using a portable drill, affix carriage bolts through both edges, then bolt the cone to the brackets. For 4"x4" posts, if ordering from the Prairie Pothole Chapter, choose "MWI" type cone. No brackets are needed with this cone since the MWI type is made with four "wings" which are bent back to fit snugly around the post. Drill pilot holes through wings, then use deck screws on the fender washers to attach wings to post. No gaps remain for snakes or mice to access box. Video at www.prairiepotholeday.com Paint the cone earth-tone color.
Placement: Ideally, choose a site near a wooded area and close to a clean wetland with a strong aquatic insect population. Both the egg-laying hen and her ducklings require a diet rich in aquatic invertebrates. Face the hole toward flight lanes or an adjacent wetland. If you are lucky enough to live near good habitat, angle the box so you can see part of the hole from your breakfast window. Squirrels can leap eight feet horizontally from tree trunks, and drop eleven feet from overhanging limbs, so plan accordingly.
Heat: Pole-mounted boxes are seldom in complete shade. Boxes made of metal, insulated plastic, and even plywood, when exposed to direct sunlight on hot June days, can become way too hot for the hen and her eggs. White paint and vent holes help, but it’s better to choose boxes built with natural wood. Wooden boxes have been shown to be the best at resisting heat build-up.
Teaching Bonus: By using the Best Practices mounting method, a youngster can not only help construct a box, but can also safely participate in placing and monitoring it. Watch for the smiles when small children climb on top of a five gallon pail and find out they are nose to nose with (and can touch) a growing clutch of eggs.