Sunday, March 31, 2013

Bluebird Boxes Offer insight Into Bird Behavior

The male Bluebird checks out one of our Bluebird Boxes

I started to clean out the nature preserve’s Bluebird Boxes last week. The calendar told me it was time to do it, even if the weather didn't quite agree. In fact, there was an impressive snow squall taking place when I did the boxes in our largest field. Despite that, a pair of bluebirds stayed nearby – the male was singing and both birds were checking out one of the boxes only minutes after I had cleaned it.
The female bluebird  warns off a swallow that shows interest in her box
Cleaning boxes probably sounds like a mundane task, but I actually look forward to it. I get to examine the nest designs of well over one hundred bird architects. Primarily, the builders belong to just a handful of species, but individual birds belonging to the same species can have their own unique style.
The male Bluebird preens as the female checks the suitability of a nestbox 
An extremely feathery Tree Swallow nest freshly removed from one of the boxes
Tree Swallow nests are the type most commonly found in our boxes, and these nests are most often decorated with feathers from other birds. Some swallows only make use of a few feathers, while some go all out and use dozens of them. All feathers are not equal to the Tree Swallow – some types are ascribed much greater value. Although they must be difficult to come by, white feathers seem to be especially prized, and it seems as though Tree Swallows must put some considerable effort into obtaining them. The majority of the white feathers that I found in the nest boxes this time belonged to Ruffed Grouse – a bird that incidentally, is not known for its white plumage. The whitish feathers come from the grouse’s underside. 
Feathers of Cedar Waxwing, Blue Jay and grouse decorated the nest in this box 
The tip of the Cedar Waxwing feather shows a red waxy projection
So an interesting thing about Tree Swallow nest is how they can help you determine some of the other bird species that are residing in a given area. This time, the feathers of over one dozen bird species were found in the nests, included those of Wood Duck, Cedar Waxwing, Blue Jay, Red-tailed Hawk and Cardinal. Other birds incorporate feathers into their nest designs, but they don’t usually do it with the same panache that characterizes the Tree Swallow’s efforts. House Sparrow and House Wren commonly use nest boxes, and both species will sometimes use feathers. The latter species uses feathers much in the same way it uses twigs – just as building materials and not as decoration or insulation. One of the wren nests I looked at the other day had about a dozen bluebird and cardinal feathers enmeshed in its twiggy support structure. I recall once a Screech Owl that had a similar gaudy collection of feathers on the floor of its nest box, but in that case it was Blue jay and Cardinal feathers. At the time I surmised that feathers came from birds that the owl had eaten.
Beneath the Tree Swallow nest was a Bluebird nest with an egg still in it
A House Wren jammed this box completely full of twigs
Often more than one nest will be found in a single box – representing the use and reuse of a box by multiple pairs of birds in a single season. Typically, there would be a Tree Swallow nest or a Bluebird nest on the bottom level, with a Wren nest or a House Sparrow nest build on top of it. In some cases, possible foul play is indicated. In one instance, I suspected that the lower nest was still being used when the new owners came to claim the house. For beneath the Tree Swallow nest, I found a bluebird nest with an egg still in it. Now did the Bluebird abandon the nest before the swallows decided to move in, or were they driven out?
Long after young  fledged from this swallow nest, a mouse used it  for a place to cache seeds
This mouse nest was built on top of a Chickadee nest - note the green moss from the Chickadee layer
This mouse nest is made mostly from cattail down and grass
Mouse nests (most often  belonging to the White-footed Mouse), are often found in our Bluebird boxes. The mice move into the boxes in the fall and there they remain to raise at least one brood during the winter. Last winter a large proportion of our boxes held mouse nests, but not this year. This time only 20 or so boxes hosted nests and most of those were  already abandoned by the mice by the time I came by. Whenever I find an active mouse nest, I of course, leave it alone and allow the mice to finish their breeding cycle before removing it. 
This mouse nest is made almost entirely from bitten off pieces of milkweed silk

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