22 April 2014

Bird prints on windows are caused by "powder down"

In the middle of April we experienced several days of truly bizarre behavior by a local robin.  Perched on the railing of the porch, or in the branches of a nearby juniper, he would launch himself against one of the windows.  Repeatedly.

These strikes were totally different from the rare high-speed bird strike that happens when the creature fails to detect the presence of window glass and breaks a neck.  These assaults were "belly up" flailing at the window, at low speed, and with true deliberation, repeated in series of dozens.

Had this occurred in midsummer, I would have surmised that the bird was chasing insects drawn to the window, but this was daylight with no house lights to draw insects (and essentially none present at this time of year).

Several windows of the house were "painted" with overlapping "bird prints" similar to the one shown above (via The Soul is Bone).
The imprints are caused by the bird’s powder down, a special type of down which helps feathers to grow. In some species, the tips of the barbules on powder down feathers disintegrate, forming fine particles of keratin, which appear as a powder, or ‘feather dust’. When a bird strikes a glass pane, the power is shaken lose and adheres to the glass.
We wondered whether the bird was mentally deranged, but finally found the answer after a brief internet search... (explanation below the fold to allow you to ponder the problem)

"Another cause of window collisions is male birds defending territories during mating season. They will see their reflection in the glass, believe that it is another competing male, and attack the glass repeatedly in an attempt to drive the intruder off. Two of the most common species to exhibit this kind of behavior in the metro region are robins and flickers."
Makes perfect sense.

Photo credit.


  1. There's a robin that has been doing this to my car window for 2 years now, it will attack it, then sit on the window-seal and crap in frustration, right down the passenger side door. I put one of those hawk silhouette stickers on to try to deter him, now it just looks like the sticker took a huge poo on the side of my car

  2. I had a Cardinal down ere in Texas that used to attack the window on the back porch from a plant stand. I moved the plant stand a few times , and he stopped. He stopped, until he showed up at the bathroom window. I guess some birds are just looking for a fight.

  3. Cool-Robins are the most territorial birds I guess. We get this with only pigeons, who are rather stupider, bless 'em

  4. At the Honolulu Zoo there was a cardinal who spent a lot of time attacking side view mirrors in the parking lot. The animal keepers called him "Studley."

  5. Watched a robin refurbishing last year's nest several days ago, only to find it occupied by a morning dove the next morning. Dove is still there, but the robin's still crapping on the deck nearby.

    Sharks and Jets time coming up, ladies and gentlemen?

  6. When we lived in Cincinnati, we had a cardinal that would dive bomb our kitchen window from a perch on our neighbor's roof. He also would sit on the brick window ledge of a lower level window and peck at the window. We always thought he saw his reflection and thought it was another male to drive off.

  7. I wonder if Tinkerbell ever left Pixie Dust whilst defending her territory.

  8. We had an insane cardinal that would repeatedly slam himself into our kitchen window in the late morning hours for weeks on end. He came back three years in a row. I could never fathom how he could slam himself into the window over and over, year after year, and still have enough undamaged brain tissue to make his way back the next year. The cardinal would drive my fox terrier into a frenzy - hours of SLAM! barkbarkbark.... SLAM!!barkbarkbark.... Fake owl statues, hawk silhouettes, colored paper on the windows - nothing deterred that hideous bird.

  9. Our crazy bird is a mockingbird who nests in the tree outside the dining room.


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