Warning! There is a slightly gross photo at the end of this post.
In the photo on the left are nests found in one Gilbertson Bluebird Box. From left to right we have a black-capped chickadee nest, a house wren nest and an eastern bluebird nest.
It's the time of year to start cleaning birdhouses. One of the people I birdscape for had a Gilbertson Bluebird Box that had been used at least twice this summer. When I put it up last spring a black-capped chickadee moved in right away. Before I had a chance to clean it out after the chicks fledged, a bluebird pair moved in and built a new nest on top of the old chickadee nest--this is not supposed to happen, bluebirds are supposed to want a cleaned out box, but again birds don't read the same books I do. When I went to clean out the nest box the other day I discovered a HUGE pile of sticks on the inside--house wrens. The last time I checked the nest box, there were bluebird chicks inside so I knew that meant the wrens hadn't damaged the bluebird eggs. Since house wrens have a tendency to make several nests using all but one as decoys, I figured this was a decoy nest. I know that you're supposed to check nest boxes once a week, but I don't regularly visit this client's house and I really wasn't expecting a third brood in the nest box so I hadn't bothered checking it after the bluebirds left the box.
I took the box down and looked inside and found feathers lining a small pocket inside the box, could the wrens have actually raised a brood in the box? I looked at the layers of feathers and sticks inside the box, as I was looking it over I noticed an aroma--a familiar aroma. I knew I had smelled it before, but couldn't quite remember. Then it hit me--pelicans! Now, none of the birds that nested in the box don't eat fish, so that wasn't the smell, I was smelling death. I started picking through the feathers among the sticks and found cardinal feathers, bluebird feathers, ruffed grouse feathers, a downy woodpecker feather and then a small wad of teeny tiny bones held together with some dark matter and realized what I'd been smelling, very old death. Looks like one of the wren chicks didn't make it. Who knows the reason, it could have been deformed at hatching, it could have gotten an illness, it's tough to say. It could also have been that there weren't that many eggs and none of the wren brood survived.
I dug out the rest of the wren box and got down to the bluebird nest that was a nice and neat little cup of grass and pine needles. There were no shells or dead chicks so all the young bluebirds made it out of the nest which was a relief to discover. I made it down to the bottom of the box to where the original chickadee nest had been. The chickadee nest looked more comfortable than the bluebird nest, a cozy cup full of moss and fur. Apparently one of the eggs didn't hatch. When I checked the box while the chickadees were nesting, the chicks were so crammed in there that I never saw the egg.
After the fun I had opening the merganser egg, I decided to check out what was inside the left over chickadee egg. I carefully pried open the shell and found a gross brownish yellow liquid, with what looked like a partially formed chick on the inside. Perhaps this was the last egg laid and didn't get brooded as long as the other eggs so it never fully formed or maybe something went wrong internally as the egg was developing, again you really can't say why it didn't hatch. It just one of those things that happens and one of the reasons why birds try to have some many chicks in the season since so many never make it.
So if you haven't cleaned out your birdhouses yet, now is the time to do so. First check and be sure no one is till using the box there is a chance some bird is finishing up a final brood. Even if you haven't seen any activity around the nest box, it's still a good idea to open it up and clean it out. You can check and see what is going on, maybe you have had something else move in the box for the summer like a flying squirrel, a wasp nest or on rare occasions a bat! After you take out the contents of the box it's good idea to clean it out with a mild bleach solution and then let the house dry out in the sun. Many people take their houses in for the winter to keep mice from moving in or some people leave them up for birds to roost in at night during those cold winter months. If you go for that option, you will have to clean out the nest box again in March on the off chance that house sparrows have started nesting early. Once house sparrows get hold of a bluebird house, they won't let anyone else use the box ever.
And so on a final note, it occurs to me that I should leave a photo of the house that the birds used. This is a Gilbertson Bluebird Box and it's one of my favorites to use, since it's easy to clean and open up. House sparrows and starlings seem to not care for the design of the house but tree swallows, bluebirds, chickadees and wrens really like it.