Sunday, May 6, 2012

Bluebird Trail, Week 6 - 20 Nestlings!

This week sped by, and we did not visit any of the nestboxes after Monday. As a result, the photo I posted last Tuesday of the Box 9 nestlings on day 8 will be our last photo of them, unless we are lucky enough to get any photos after they fledge. Today (Sunday) they are at day 14 since hatching, and standard bluebird monitoring advice is not to open the box from about day 13 on unless there is a compelling need, because it is too close to their fledging date (most often 17-18 days, though it can take several days longer).

By day 13 or so they are fully feathered, and the fear is that they may be startled into fledging prematurely, which could endanger them. This risk is thought to be less with the top-opening Gilbertson boxes we are using than with front-opening or side-opening boxes, but we don't want to take any chances. But we will try to stop by later this week, and in the weeks ahead as we continue to monitor these boxes, to see if we can see any sign of them out and about with their parents. The male, in particular, will continue to tend to them for several weeks to come; mama, in the meantime, may start building her next nest almost immediately.

Box 5 nestlings at Day 4 

Our fourth clutch of eggs, at Box 5, hatched probably Tuesday or Wednesday last week, and so were about at day four when we stopped by on Saturday (above). You can see some feathers lining this bluebird nest.

Tree swallow nest - note prominent, curling feathers. No eggs yet.

We were able to get a photo of the tree swallow nest in Box 15 (above) on Saturday. Bluebirds and tree swallows both make their nests of dried grass, but tree swallows make much more liberal use of feathers in the nest, and the feathers tend to curl up to surround the eggs (though there are no eggs yet in either the box above or the one below), rather than merely lining the nest. We have seen small feathers in several of our bluebird nests, such as the one with the nestlings above, but in comparison tree swallow nests are very feathery indeed.

Tree swallow nest on Trail 2 - no eggs yet

Above is another tree swallow nest. It is from the other set of boxes we are temporarily (?) looking after. We'll call those boxes Trail 2. Currently there are four nestboxes on Trail 2 -- two are paired, and the one above is one of those. There are two new bluebird eggs in the other box of this pair, and we have five new bluebird nestlings in one of the other boxes as of Sunday. We're waiting to see what develops in the fourth box, which contains a grass nest that looks as if it could be either a bluebird or a tree swallow nest at this point.

I am somewhat concerned about tree swallows using these Gilbertson nestboxes we are monitoring, ever since reading the opinion of the author of that these boxes, which have just a four-inch diameter, are dangerously small for tree swallow use, since tree swallows have larger clutches than bluebirds. People who put up nestboxes specifically for tree swallows are urged on that website never to use a box with a floor area smaller than 5 x 5 inches. I suppose cavity-nesters take what they can find to some extent, both in the course of their long natural history as well as in this age of humans providing nestboxes. One would think that a bird would "know" if a nesting cavity is too cramped for success, and would avoid it, but the treeswallowprojects site says that is, sadly, not the case. I will be interested to find out from Minnesota bluebirders who like the Gilbertson boxes what their experience has been with raising healthy tree swallows in them.

Below is one of the Trail 2 tree swallows, who sat very quietly nearby while we checked the box nearby and returned to this post when we walked past again after checking the other boxes. Tree swallows (and bluebirds too -- see below) are quite capable of diving at you from the air if they think you're too close to their nest, so we were quite surprised that this one did not display any aggressive protective behavior, though it was certainly watchful.

Tree swallow on fence wire

I took this next photo last weekend. I like the near-dusk softness of the landscape surrounding this handsome male bluebird.

Male bluebird at dusk

Box totals from our regular trail: 20 nestlings! There are five nestlings each in Box 9 (about 14 days old), Box 16 (about 12 days old), Box 14 (about 10 days old), and Box 5 (about 5 days old). As far as we know, they are all healthy. We did not look inside Box 16 this weekend, because the parents did dive at us when we approached the box, so we probably will not see those nestlings again for the same reason discussed at the start of this post -- they will very soon be too close to fledging.

There are still three pink eggs in Box 18, which is the same number as there were a week ago. They felt cool to the touch yesterday. The parents are always nearby and very vigilant, but we're not sure the incubation is proceeding as it should, so that is worrying. Stay tuned...

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