Mystery Bird Imprints I work at a school that has a 2nd floor passageway connecting two buildings, pictured at left, which has been nicknamed the "gerbil tube" because of the large circular windows. On June 7, 2004, mysterious imprints of two birds were spotted on the outside glass of the south window. One of these amazingly detailed imprints is pictured at right. Obviously these birds flew into the glass. Just what mechanism was at work to make the imprints stick to the glass is the first mystery. The second mystery is trying to figure out what kind of birds these might have been. The photo at left shows both imprints as viewed from ground level, looking up at the window. The buildings are reflected in the glass, the light fixture on the ceiling of the passageway is at the top, and you can see through the round window opening on the opposite side of the passageway in the bottom corner This is a telephoto view, as the window is a little above the 2nd floor level. The photo at right shows the upper imprint, which had far fewer details than the lower imprint nearer the handrail. It looked a bit smeared and fuzzy, which might indicate it was approaching the window at more of an angle, and must have slide more when it hit. This might explain the smudged quality of the imprint. The only sharp details are in the wings, which left incomplete imprints. The chest, head and tail imprints were much less distinct, though it can be seen that the tail was spread and both wings were out wide as if braking for a landing. This image was taken from the outside at ground level, since its position on the glass made it impossible to get a good image from the inside due to glare and the background behind it. Since the lower imprint was more detailed and easier to photograph, it will be the one more closely inspected. The photo at left shows the window from the inside. The imprints are marked since they are very difficult to see with the glare and reflections on the glass, unless you are at just the right angle. This made taking useful photos a bit difficult. Note the handrail that crosses the window. Judging from the positions of the imprints on the glass in relation to the handrail, and the fact that the lower imprint plainly shows the birds tail feathers fully spread and its head imprint looking down, it appears the birds were angling downward, and were braking for a landing on the handrail when they hit the glass. This conjecture is reinforced by the fact that no dead birds were found, also indicating they were not flying very fast when they hit, and therefore were not injured to any extent. Had they been flying "through" the passageway via the two perceived large round openings, they would logically have been going much faster, and very well might have killed themselves. I do not believe the imprints could have looked as they do, had they been flying head-on "through" the "opening". Click any image for an enlargement. Whether or not these assumptions are correct, the real questions still beg answers. How were the imprints made on the glass, and what kind of birds were they? I'm not qualified to answer either of these questions. I can only offer some logical guesses, and provide some information so someone more qualified might answer them. As to the first question, the imprints almost looked like what you see when a butterfly hits glass, and leaves some of the fine scales from its wings, something like a fine dust, which makes an imprint. But since I don't believe any such thing is possible with bird feathers, I have to speculate that the medium for the imprint is the oil from the bird's feathers. Perhaps moisture, airborne dust and pollen clinging to the oil made the imprints visible. A full two weeks after this event the imprints were still quite visible and distinguishable, and have lost little of their intensity and detail, in spite of several intense summer rain storms during that time. As to the identity of these birds, my initial guess was common pigeons, since pigeons are a frequent sight on the cupolas and roof ridges of the school buildings. They would also be large enough, I would think, to fit the measurements shown in the upper left images, which indicate the measurements on the glass. However, the shape of the tail feather spread did not seem consistent with pigeons. After some researching, I decided the only logical fit was Mourning Doves, which are quite common here, though I don't recall seeing any on the campus. The measurements fit, and even the imprinted shape of the head and bill seem right. Head & tail details Note that all these photos are taken at about a 45 degree angle to the glass to minimize the glare and reflections, and to place the shaded area of the brick in the background behind them, making them more visible. This angle means the photos exhibit a bit of perspective, and the imprints appear slimmer in the width-to-height ratio than they actually are. It gives a bit of a false impression of the wingspan compared to the body length. Separate photos had to be taken of the wing/body, and the tail/body for the imprints to be visible against the background as well. Attempts to get the full imprint in a single detailed photo, or to shoot the images square on to the glass and have them visible or distinguishable were not successful. Because the glass was not accessible from outside (2nd story) I was unable to employ other photographic tricks to improve the photos, such as to introduce a controlled background or block light and glare with large panels. What I have here is simply all there is. Perhaps these measurements and the detailed head and tail photos will provide some more qualified bird experts the necessary information to speculate on the identity of these birds.
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