Having lived in Austin...
And given that the dead birds are Grackles - I would not be at all surprised if someone took it upon themselves to poison them-they are noisy, messy, foul fowl.
They would congregate by the hundreds of thousands on the UT campus- the racket they made was deafening, and their droppings were so copious that they made bike riding hazardous, and the stench was overwhelming. Hatred for these birds was ubiquitous. Pigeons are FAR less annoying.