Yesterday when we checked the box after our walk around 10, we found bluebird remains on the ground outside the box. There were two pieces of wing and a tuft of feathers on the post. Inside, we found an empty box, fresh poop, 2 small spots of blood, and 2 feathers. For two full days, we've tested all sorts of hypotheses about what could have happened to the little ones. Here's a smattering of what theories we've floated.
1. A snake got in the box. Refutation: the snake would have plugged up the whole and not allowed them to escape and would have still been in the box when we checked it.
2. A House Sparrow attacked. Refutation: he would have attacked all the birds, leaving all of them injured or dead inside the box.
3. A raccoon attacked the box. Refutation: the box would probably have been on the ground and/or the latch opened.
4. A cat attacked the box by sticking its paw inside the hole. Refutation: there would have been a lot more blood and feathers inside and probably more than one dead fledgling.
5. There was a problem during their fledging. Refutation: its not impossible, but they were still 2 days away from a normal fledgling date. This explains the remains outside, but why the spots of blood inside?
At this point, all we know is that one bluebird fledgling has died. We believe that because we haven't seen any activity around the box by Mama, Papa or the first set of fledglings, there are 3 fledglings in a tree somewhere. When the first group fledged, we didn't see them for over one week and didn't see much of the parents during that time either. This is why we think that the parents (and the first fledglings?) are protecting and feeding the new fledglings. It is still a mystery as to how the one died. Did it fall from the nest during fledging, hit itself on the barbed wire under the box and get carried off (or at least most of it) by a predator? That is the explanation that we're going with for now. We have to believe that all is alright with the other 3 and that the cause of the death was due to immaturity rather than predation.
I cleaned out the box yesterday and reinstalled it today after witnessing Mama and Papa near its old location. Bluebirds begin their annual molt around now, so it is unlikely that we'll have another brood. Males grow infertile and females are unable to conceive during their molting cycle because doing both would cause death from too much physical stress. Molting wears them down and even if they could successfully mate, the stress of feeding and caring for a brood might be too much. But I feel better letting their instincts tell them what they want to do instead of taking down the box and forcing them to make a decision that they otherwise would not make.
We are leaving town tomorrow morning. I am agonizing over the fact that we won't be here for a whole week. I suppose that I wouldn't see the fledglings during that time even if I were here, but because there's a chance that they could appear, I want to be here. The only thing I can do now is hope that when we return, we'll see the little ones hanging out with their family.
Paul and I have been very saddened by the death of the one fledgling and the possible loss of the others as well. We realize that these birds are not domesticated animals and have a high mortality rate just by virtue of being seen as food by so many other creatures. But a loss is a loss. The best we can do is figure that if the 3 do survive, the survival rate of the box this year is still over 50%. Small comfort, but comfort nonetheless.
Posted by Elizabeth at July 19, 2004 10:15 AM