This photo is neither flattering to subject nor situation; you'll have to assume that the window is as darkly tinted and highly reflective as any window can possibly be. The building is not a house in this case, but the gift shop at the Persimmon Gap entrance to Big Bend National Park. The title stands for weary googlers who are searching for a reason that a bird might be trying to get into their houses and/or attacking their windows (and side mirrors on cars! Easily enough prevented with paper or plastic bag securely placed over side mirrors, but then shiny hubcaps get the attention...)
The charming, witty, amorous suitor in the photo below is a Common Raven, making soft gutteral noises and bill-clacking to the lovely, svelte raven-in-the-mirror. At least we can only assume that charming and witty are attractive to ravens... the sweet nothings sure sounded charming.
Many of the questions I get about birds & windows are based on the assumption that the bird is actively trying to get into their house. Having not seen every situation on the planet, I can't rule that out, but in every situation that I've personally seen, the bird "trying to get in" is either defending territory by trying to attack the intruder it sees (itself), or, as is the case with the raven above... the poor critter just wants to say 'hello' to the attractive creature in the reflection.
The instinct for a bird to approach its reflection is pretty basic, like a baby in front of a mirror. There is no need for fear, panic, alarm, etc. While taping a piece of paper over the window might stop the bird from attacking that particular spot... well, there's still the rest of the window, right? This is good and bad; it means the bird can still attack a lot of window, but it also means that there's a lot of room to play.
Click here for an example of a Northern Cardinal attacking a window - via birds and buildings.org ...apologies for the gratuitous linking, as their photo is from my first round of undergrad adventures, but it demonstrates the "single piece of paper" theory in action (and failure).
One of the most simple examples of effective bird deterrence is this: the humble post-it note. Spacing them in a checkerboard pattern across the inside of a window is about as temporary and easy as it gets. Depending on the bird, it may only try to attack the window for a week or two; some may express territorial behaviors for a month or more.
Both of the post-it note photos are courtesy of Pauline Saribas, who used the design to prevent lethal window strikes (as opposed to territorial strikes) - but the idea is the same; make the window as unattractive of a suitor/challenger/flying space as possible. The large "x" shape is unlikely to deter many strikes, lethal or not, because there's too much room around the shape, but if the entire surface was checkered the number of strikes would certainly go down. Hopefully the best "attacking" spots would be well concealed, thus ending the reign of Pecking Cardinal, Swooping Flycatcher, Flailing Mockingbird, and Heartthrob Raven.
While a bird attacking a window is a nuisance to humans, perhaps, it is a distraction from what the bird should be doing - raising young, defending their territory from real birds, and generally going about their business. It is NEVER acceptable to kill the bird as a "solution" - it dooms their offspring and is illegal.
Go with the easy on, easy off, inexpensive, temporary and otherwise humane option of post-it notes. You can unleash your creativity with bright colors, bold patterns, crafting them into fun shapes and designs, and maybe even get the territorial bird away from your window(s). It could, however, get your neighbors wondering!
Other sites relevant to birds and windows:
FLAP.org has a section on "prevent window kills" with some very nifty links - they address a lot of things that do *and* don't work, as well as *why*
Project BirdSafe - for home & office - you don't have to be in Minnesota to appreciate their guidance!
This is geared mostly toward architects, but under "INFORMATION ABOUT
BIRD-SAFE DESIGNS" the "solution options" have some really cool
examples of modified windows - birdsandbuildings.org
Feel free to leave a comment or drop an e-mail if you'd like help addressing collision issues - territory or otherwise - it's always worth kicking around ideas to find what works in different situations!