Okay, you can’t mention the latter band without giving the link to the thread that gave birth to their name.
So, without further ado, from 2001 no less, here’s one of the classic SDMB threads:
I always know when the mulberries have ripened when I start seeing purple bird poo.
Oh, my. That sounds like quite the predicament of the avian variety. I empathize with you, really I do. My mum’s parakeet was quite the filthy beast herself. Befouled the dickens out of the Morning Times, it did.
It never ceases to amaze me how our family birds can generate a morning deposit seemingly equal to their body weight and volume. Maybe they’ve evolved organic Tardis technology.
Yes…that’s right…completely made up.
Shhhhh…let it be a suprise 
Yes!!! And a hearty “fuck off” to both the birds who gorge themselves on the berries in the tree by my driveway (with predictable results), and the HOA for not letting me cut the damn tree down. A special “what the fuck were you thinking?” goes out of the now-defunct developer, who apparently got a really good deal on these trees from somewhere judging by the number of them present in the yards of houses they built.
My uncle used to tell a story from when he was working in the town of Emerald, in Queensland. He worked in the local bank and an inspector/auditor who was not well liked came to town to have a look at the bank’s operations. The inspector parked his brand new car next to a mango tree behind the pub/hotel he was staying in and walked to the bank the next day.
Of course the Flying Foxes came in overnight, gorged themselves on fruit and then proceeded to lighten themselves when they took off in the morning.
When the inspector returned that evening he found his car covered in a hard-baked covering of bat shit and regurgitated mango.
Indiscriminately shitting on things and trying not to be noticed? I’m thinking Tony Abbott.
During Franklin D. Roosevelt’s presidency a headline read: FDR LEVELS BIG BLASTS AT CHAMBER 
It is with some trepidation that I offer an element of fact into this otherwise – uhh – fact-light thread. To wit:
Birds of prey, (like hawks), literally squirt their feces. My smaller hawks send a shitstream a couple of feet. My eagles can liberally decorate a wall nearly 2 meters away. The deposit is usually mostly brown, with some white urates. I’m not sure what your locally equivalent birds are, but if they’re diurnal raptors, I’ll bet they are squirt shitters.
Now THAT’S a tongue twister. 
So…pictures at 11? Or can we see them sooner?
What time zone are you in?
I have a pair of cardinals that decided they desperately need to get into my house for weeks now. Four windows on the corner on both floors are covered in bird spit from them banging their heads into the glass.
Flying rats, that’s all they are.
How about Lories or Lorikeets?
kayaker, all the Psittacines I’m familiar with are “drop down” poopers. The OP describes situations wherein merely dropping feces wouldn’t produce the result s/he sees. That’s why I suggested raptors, which actively squirt their shit.
Sitnam, take some dry laundry detergent and mix it with a little water, making white paint. Paint the outsides of your cardinal-targeted windows. Probably just the lower foot or so should do. The birds are attacking their reflection, seeing themselves as an intruder. The more often they see their image, the stronger becomes the compulsion to check back again, sooner. Break the self-reinforcing behavior by removing the reflection. Leave the “paint” on for a week or so, then hose it off. You’ll have cleaner windows, and with luck the cardinals won’t immediately rediscover their hated enemy.
I once had a rainbow lorikeet (Trichoglossus something). A nectar eater, it would cling to the front of the cage and shoot a stream of wet waste.
But I agree raptors are more likely given volume.
Also, I’ve had some exposure to Great Blue Heron waste. Blech!!!
Fruit bats ****Kam. They do it to my neighbours walls too. How they get it under the eaves is a mystery but they do.
Prehensile cloaca?
Them’s gotta be the culprits then. I haven’t actually seen any around, but then I’m not outside at dusk because it’s too bloody cold to stick my nose out at that time of day.
I believe it’s going to be ‘fine’ tomorrow (as in, no rain) so I’ll attack the walls with a scrubbing brush and hose then!
Oh, for those suggesting raptors, not where I live!