A friend of mine works in manufacturing plant in which birds tend to make their way in through some large vehicle entrance openings. This was a particular problem for him and some other support staff. They were located on the shop floor with privacy walls but no ceiling. Many of the birds would camp out high above his work area and relieve themselves. This made the desks, computers, file cabinets, chairs, etc., a bit messy.
Soon the staff erected little cardboard huts to protect themselves. They would huddle under the huts working on their computers and occasionally hear a loud splat overhead. His management tried feverishly to come up with a solution to drive the birds out including fake owls, strobe lighting, and, worst of all, Justin Timberlake music. Even the music didn't drive the birds away but it did increase the sick leave usage.
I came up with a brilliant idea for him to pass along to his management. When I had visited an IKEA, they had covered parking. Their solution to keeping birds away was to play recordings of predatory bird calls amplified throughout the parking garage. Since my friend's company didn't have the budget for a sound system, my solution was to train each of the staff in bird calling. They could take turns every couple of minutes calling out. Here's a recording of myself with an example:
Of course, they'd have to make sure they didn't accidentally do mating calls or the place would be filled with male hawks ready for action.
Speaking of mating calls, you definitely need to read this Darwin Award out of the Dallas Chronicle before you go messing with animal calls:
A man in Sweetwater Texas wanted to see just how many bees he could attract by modifying the pitch that was emitted from his Polk Audio speakers connected to his home theater system. What he did not realize was the pitch did not attract bees in the slightest but was precisely the same sound made by the female West Texas Yak during mating season. Upon hearing this sound, a male yak showed up ready for action only to find a man sitting on one of the two Polk Audio speakers. The yak's reaction was to gore both speakers and the man. Officials on the scene were overheard saying that the man may have avoided this had he been using Realistic speakers manufactured by Tandy.