The Wood Duck Society Board of Directors, at our January, 2004 meeting adopted a
“Best Practices” method of nest box mounting. The method involves bolting a
wooden box to a pole, with the hole just six feet from the ground. A
sheet metal
cone predator guard is placed just below it, with its lip at least three
feet from the ground. The box should have a side-opening door, allowing
monitoring to be done on a walk-up basis. No ladders are ever necessary.
Cone Rationale: This technique is not new. In 1958, a drawing illustrating a
nearly identical box and cone method appeared in a U.S. Fish & Wildlife leaflet,
written by Clark Webster. No predator guard is 100% effective against mammalian
predators, but this one comes very close (In northern Minnesota, however, bears
remain unimpressed). My southern friends tell me that rat snakes, when five foot
and longer, can shift enough of their weight over the top of a three foot cone
to allow passage to the box. And avian predators, of course, are not deterred.
The cone guard has stood the test of time. Bellrose and Holm, in their book,
Ecology and Management of the Wood Duck, published in 1994, stated: “When
constructed to the proper dimensions and snugly fitted, cone shields provide the
best available protection against pole-climbing predators.” On my own 100 box
unit in Minnesota, on a wooded farm rife with raccoons, mink, and squirrels, I
shifted in desperation to this technique over twenty years ago. The mammalian
predation rate, when eggs, hen, and brood are in the box, promptly plummeted to
zero and has stayed there. Nest competition from squirrels is no longer a
problem here.
The perception seems to be that cone guards must be difficult to construct, and
might be too expensive. Neither perception is true. Jr. High students at a
summer waterfowl camp routinely learn to affix the cone in less than ten
minutes. Cost for cone, brackets, and peace of mind =$10 (see sidebar for
sources).
Usage: Wood duck hens use (some studies have found they prefer) low-mounted
boxes. Higher is not better, only more dangerous and difficult. Expect nest
success with this system, and expect successful hens to come back, along with
some of their female offspring, if they survive the rigors of migration and
wintering.
Tools: Portable drill with bits, wrench, and Vise-Grip pliers. The Vise-Grips
hold the overlapped edges of the sheet metal in a cone shape after it is wrapped
over the supporting brackets. Holes are then drilled, and small carriage bolts
used to fix edges together and to attach cone to brackets. Paint cone an earthtone color.
Poles: The strangest reason for resisting the pole-mounting method is the
tenacious, almost visceral, and sometimes dangerous need to bolt boxes onto
trees. This ladder climbing may persist for years, often including unending
battles with mammalian predators, since trees are difficult to make
predator-proof. Thirty years ago, I used to stay awake nights, dreaming up
questionable schemes to retrofit my tree-mounted boxes in an attempt to make
them less hospitable to predators.
Without ever gaining inside access, raccoons on top of a box can cause a hen to
abandon her clutch. Even worse, when the harassed hen sticks her head out, she
may lose it to the raccoon.
In contrast, poles allow easy attachment of effective predator guards. There is
then no need to retrofit boxes with add-on features designed to discourage
climbing predators. Key: Keep predator from reaching the box in the first place.
Eight-foot treated landscape timbers (flat on two sides) work well and cost $4.
Using a post hole digger, carve a hole two feet deep. Place pole, tamping dirt
firmly around its base. Bolt box to pole so the bottom of hole is six feet from
ground. If discarded stop sign poles are available, pole placement is easier and
cheaper, and can then be done in wet areas as well, joining two or more sections
together as needed. Bolt support brackets right below the box, and affix cone
guard, as described above.
Placement: Wood ducks have evolved to nest in tree cavities. Place pole-mounted
boxes near trees and near brood habitat, where they will be found easily by
cavity hunting hens. However, gray and fox squirrels can leap 8 ft. horizontally
from tree trunks, and drop 11 ft. from overhanging limbs, so plan accordingly.
Heat: Pole-mounted boxes are seldom in complete shade. Temperature studies have
shown that boxes made of metal, plastic, and even plywood, when exposed to
direct sunlight on hot days, can become too hot for egg survival (107 degrees
F.). The hen may abandon well before that point. Studies done here (Newsgram #
16, Dec. 1995), found that metal and plastic boxes reached 118 degrees F. on a
94 degree June day in Minnesota. White paint and vent holes help, but it’s
better to choose boxes built with natural, 7/8” thick boards. Such boxes resist
heat build-up on sunny, hot days.
Teaching Bonus: This “Best
Practices” mounting method allows safe, hands-on
teaching. Even small children can be brought nose-to-nose with the eggs by using
a simple step stool. If you doubt the value of this, try it, and take a look at
their faces. The wood duck box just might be the best ecological teaching tool
ever devised.