Warning for the squeamish and youngsters: this series of posts will have photographs and descriptions of a dead bird in various stages of decomposition.
Days 2 & 3
On day 2 (two days after I found the dead bird―day 0 is here), there were several flies trapped inside the box. I had punched holes thru the walls of the box to let the flies in, but once inside the box they were apparently having difficulty locating the holes to get back out.
These are blow flies (family Calliphoridae). They can detect the smell of a dead animal from far away. Female blowflies deposit their eggs on carcasses. After I opened the lid I also saw many ants crawling on the bird. I also noticed that the bird had started to smell (day time temperatures had been up to about 33°C). But, otherwise, it still looked intact.
On day 3, there were more flies and ants on and around the bird, the appearance of which had changed since the previous day. There were many loose small feathers around and the tail feathers had fanned out, indicating that the skin and the flesh had been breaking down.
The bird also smelled stronger than before and the odor was similar to that of rotting fish. This is the smell of various amines that are probably produced when proteins are breaking down.
Tomorrow: maggots galore
More information on blow flies: