|Black-capped Chickadee nestlings|
Birds in our area that cannot excavate their own nests
cavities include: Eastern Bluebird, Great-crested Flycatcher, Wood Duck, Hooded
Merganser, Common Merganser, House Wren, Tree Swallow, Chimney Swift, Eastern Screech
Owl and Saw Whet Owl. For the most part, all of these species are relying on the
kindness of strangers –meaning woodpeckers and people, to provide them with
housing. Some birds like the Nuthatches, Titmice and Chickadees, most often use
former woodpecker holes, but they can also make their own nest cavities.
recently watched a pair of Black-capped Chickadees doing just this –and it was
a slow process. For their tree they selected a broken off trunk of an Eastern
Hop Hornbeam. This was an interesting choice, since the wood of the hornbeam
is very dense, and I imagined that excavating it would be much more laborious
than if they had chosen virtually any other kind of tree. I think that what
clinched it for them was that a woodpecker had already chiseled out a starter
hole for them (woodpecker contractors probably don’t charge too much for this service.)
Also, I suspect that the tree’s heartwood was somewhat rotted, and so the wood
was likely soft enough for a chickadees’ small beak to deal with.
|Flickers commonly create cavity nests that other birds and squirrels will reuse|
As far as tree cavities go, it’s not one-size-fits-all. Some birds are very particular about the size of the entrance hole and the dimensions of the cavity itself, while other birds aren’t so picky and will accept cavities and entrance holes of various shapes and sizes. A few years ago, we had a White-breasted Nuthatch nesting in a spacious Screech Owl nest box. I guess that this nuthatch family enjoyed the high ceilings.
|A White-breasted Nuthatch enjoys the view from his "mansion"|
|A Chickadee with a beakfull of wood chips|
|The Chickadee's soft nest made largely from animal hair and moss|
The Chickadee pair worked on their excavation for at least
several days. They took turns pounding away at the wood and biting off small
beak-fulls of sawdust, which they would then release into the wind while flying
to a nearby perch. When the interior of the hole was large enough, the female
began to bring in soft nesting material –consisting mostly of moss and animal
hair. Inside the cavity, the chickadee nest consists of a thick mattress of
moss that covers the entire floor of the cavity. On top of the moss
layer, a “comforter” made primarily of animal hair is laid down. The eggs are
laid in a small cup-shaped depression in the middle of the comforter.
|Red-bellied Woodpecker reuses a nest made by another woodpecker|
Another Chickadee pair is nesting in one of our Bluebird boxes. 7 white eggs with reddish brown spots were laid into the nest and incubated by the female. It is thought that cavity nesting may be a relatively recent adaptation for Chickadees and Nuthatches, since their eggs retain colored spots consistent with the need for camouflage. Typically, birds that nest in dark cavities have no need to produce eggs that blend into their surroundings, and so most of them lay eggs that are white and/or have no spots.
The young chickadee nestlings hatched just this week, and now both parents are engaged in feeding duties.