As you may already know, I inspect the bluebird nest boxes here at the Museum each Tuesday and report on my findings (who’s doing what and where) through this Journal by the following Thursday morning. On July 12, I reported that we had only one active nest with four eggs, the nest near the Train Tunnel. I went back the following day with Emily Rush (Rentals) to give her a peek at the eggs inside the nest box. The nest was empty!
Needless to say I was a bit surprised, I had just checked the box the day before and all was fine. What had happened, was it a snake? Earlier in the season the House Wren nest that was inside the nest box in the flower meadow next to the Take Off was cleaned out by what I suspect was a snake.
We don’t use predator guards on our nest boxes, which I’ve always had misgivings about. We use 5/8″ grounding rods as the support poles for the nest boxes. When they were first installed I wondered why predator guards were not used and was assured that raccoons and snakes couldn’t climb the poles. But, as many of you know, raccoons can go just about anywhere they want to go and rat snakes can climb anything they want to climb, including a narrow metal rod. So far we’ve been lucky.
Since I’ve been actively monitoring the nest boxes most of the birds that have been hatched within the boxes have successfully fledged, flown off to start new lives. This season we’ve had one bluebird nest lost to hypothermia, one to a snake (?), and this nest (which is the same nest box which suffered the loss to hypothermia) lost all of its four eggs on the birds’ third try at a nest.
On this day, when I opened the nest box and saw it was empty I was both disappointed and saddened. I wanted Emily to see the eggs and the fact that the eggs were gone was indeed sad.
Emily noticed egg shells at the base of the support pole. There were more about six feet from the pole along the edge of the woods.
Once I saw the egg fragments on the ground I thought, “Raccoon!”
I suppose it could have been a squirrel, either flying or gray. But something about this said raccoon. Maybe it was because the animal had departed along the edge of the woods and not directly towards a tree. And, it appeared as if it had one “hand” full of eggs and was eating them as it went along. One thing for sure, it wasn’t a snake.
A close look at the nest box and I could see a hair hanging from the hole. The hair was about 12 inches long.
There was another long hair on the pole just under the nest box.
Aha, find who the hair belongs to and we found the culprit who raided the nest. The perp’s hands were probably full of sticky egg and when it went to climb down a few hairs were left along with its gooey prints on the box and pole.
But what animal has hair 12 inches long, not a raccoon. I asked a couple of the Animal Keepers, “bear, near its rear end, but not that long, even in winter,” couldn’t have been a bear.
At one point, Emily and I pondered the question of whether or not it was the hair from the head of one of the staff, but quickly realized that since the nest box side door was not open, and whoever took the eggs had gotten in through the hole in the front of the box (1.5 inches) that it probably was not a human being who reached in and snatched the eggs. Besides, the hair had a distinct synthetic look to it.
It was off to the lab to have a look at the fibers through a microscope. Master Teacher, Anna was there to help. We not only had a peek at the fiber through a microscope but she did a burn test and took a photo using AirMicro, a nifty little handheld microscope that lets you take photos directly to your iPad or iPhone. Anna also showed me a web site where one can compare the various characteristics of both natural and synthetic fibers.
Through the scope it was clear that this fiber was synthetic. Fur or hair has scale-like structures called cuticles, this fiber was smooth.
If you burn natural fibers they leave a gray or tan ash. Synthetic fibers burn, melt and shrink away from the flame and leave behind a small bead of gray, cream, or black material depending on what the synthetic material is. Our sample left a tiny, irregularly-shaped, black bead. It was either Acetate or Acrylic.
To further test the sample, Anna emersed it in fingernail polish remover. If the material dissolved it would be Acetate, if not, Acrylic. It did not dissolve. It was Acrylic.
We have already established who the thief was (as far as I’m concerned), a raccoon. But where did the fiber come from? How did it get on the nest box and pole. The how, we can figure out. It was surely stuck to the thief’s paw when the varmit climbed down the pole and since his dirty little mitts were covered with egg, the fiber was transfered to and stuck to the pole. That much we can surmise. But had the critter carried the fiber in with it from somewhere else on the campus or was the fiber already in the box.
I did a check of the box the following day and found other fibers just like the ones stuck to the pole and box. The bluebirds had apparently brought in the fiber as nesting material.
I searched for like fibers throughout the campus but have yet to find the source. Landscape Tech, Jay cut a small piece of black landscape material for me to inspect. This material is used to prevent weed growth in plant beds but there are no long fibers in that mesh material. I pulled a tiny piece of synthetic thread from the black privacy fence screen at the Red Wolf Enclosure, close but not quite right. That material appears to be acetate.
Birds are frequent users of synthetic nesting material. I once watched a chickadee pull beakfull after beakfull of nylon material from an old piece of tarp along side a river. On another ocassion I saw orioles building nests of Easter grass, that plastic grass used to line Easter baskets, following an Easter Celebration down along the Rio Grande in Texas. So, birds will use whatever material is handy, as long as it suits their needs.
But where had our bluebirds acquired their Acrylic fibers? an old shirt or sweater someone tossed out? a dog bed left outside (we’re in the middle of suburbia here at the Museum)? I don’t know. We may never know for sure, but I’m going to keep one eye peeled wherever I roam here on campus.
There are several things learned from this experience. One, we need predator guards on the nest poles. Two, I can now easily tell the difference between natural and synthetic fibers. And three, there are a bunch of very helpful and knowledgeable people that work here at the Museum who like to solve mysteries.