Woodpecker Nest Cavities

 

     In the avian world, nesting is often considered a risky endeavor. Parasitism, predators and inclement weather can all play a factor in nest failure. But through time, woodpeckers have evolved a way to minimize those challenges by simply nesting indoors, in tree cavities.

     Woodpecker activity plays a vital role in the woodland environment, excavating holes for themselves as well as for other species of birds. Black-capped Chickadees, Tufted Titmice, White-breasted Nuthatches and Eastern Screech-Owls all depend on the woodpecker’s handiwork to nest.

     Woodpeckers typically select a dying tree wherein to nest. Its advanced state of decay aids in the cavity excavation process. However, some species like the Hairy Woodpecker prefer to nest in living trees, although it may use a dead limb if needed. A woodpeckers choice of tree species vary in Connecticut, but most favor oaks, maples, hickories, poplars and birch.      

     The construction of a new nest cavity takes place each year, approximately three weeks before eggs are laid. Woodpeckers chisel out a horizontal entrance tunnels until it reaches the trees heartwood. From there, it forms a sunken chamber in which to lay the eggs. The accompanying drawing clearly shows the finished product.

From A Guide To The Nests, Eggs, and Nestlings of North American Birds
Baicich &Harrison

     Since woodpeckers do not add any lining to the nest, eggs are laid directly on the chamber floor, or onto wood chips left over from the cavity excavation.

     I have provided some additional facts regarding woodpecker nest excavations from the web pages of The Birds Of North America, online version. 

Yellow-bellied Sapsucker

In Ontario, during 3,514 min of observation, males excavated 1,317 min, females 476 min; male excavation periods averaged 17.8 min.

Bill used to chisel out cavity, striking wood at rate of 100–300 strikes/min, periodically stopping to remove chips.

Male does nearly all excavation of nest; female spends much of time preening and resting and removes very little wood from cavity, but will become more involved in excavation if first cavity not successful.

Northern Flicker

Usually excavates nest cavities in dead or diseased tree trunks and large branches, in Wisconsin, 92% of nest cavities were in dead trees.

Nest cavity is excavated by “chiseling” away small chips of wood with bill; bird starts by clinging to trunk, using its tail as a prop, then perching on lower lip of nest opening as it works its way into interior. Periods of chiseling are interspersed with shorter periods of tossing chips from cavity opening; chips are also carried away in bill.