Looking at the purple-colored poop stains below the bird, the CSI detective would probably surmise that the bird had been eating some type of fruit or berry that would cause that color to predominate...and you say there is some type of berry tree in the immediate area. Is it possible that the bird ate some partially fermented berries and became intoxicated? It happens quite often here in the winter, when snow falls and robins gather and eat fermented holly tree berries, and either get drunk and fly into windows, or simply pass out,literally dead drunk and fall stone-cold dead from the branches where they were perched and eating these fermented berries.