For the purpose of divination, the ancient Romans employed a variety of methods. One of which was haruspicy, which I wrote about for another PBP entry here. Another such method was called auspicia.
The state magistrates were in charge of “taking the auspices”, to use the modern English translation. This was done by observing birds: the type of birds, the number of birds spotted, the sounds that they made, the direction of their flight, and their location were all taken into account. Such birds included ravens, owls, hens, eagles, and vultures.
There were two different types of auspicia: auspicia impetrativa, which were signs requested from the gods, and the auspicia oblativa, which were signs that were not sought out or requested but showed themselves on their own, as a sign from the will of the gods.
Auspicia impetrativa had to be taken within a complex set of rules and parameters. To do so, the magistrate would start by putting up a tent on a spot of ground previously consecrated by the augures (augurs) for the express purpose of taking the auspices. This area was called the auguraculum, and there were three such spots in the city of Rome: one on the citadel (the Arx), one on the Quirinal hill, and one on the Palatine hill.
Then the magistrate would sleep in the tent until just before dawn, when he would take the auspices: and they were only valid for the one day and decision that were taken.
There were few reasons and events that would justify the taking of the auspices, and they all pertained to important governmental or military matters: calling assemblies, sending men overseas, battles, etc. The auspicia let the magistrates know if the gods approved or disapproved of a public action to be undertaken in the future, and Iuppiter was always asked to make his (dis)approval known before action would be taken.
Before the third century BCE, auspicia were taken by observing the flight of birds. After that, however, the preferred method was observing the eating patterns of chickens: if they ate healthily, the action was approved; if they refused to eat, that was a sign that the gods disapproved. Obviously you can see that this system was able to be easily cheated, and it pretty much was: the chickens were starved until the appointed time of the auspicium, and then they were given food, which they would scarf down.
A famous example of an auspicium gone wrong occurred before the sea battle of Drepaunum in 249 BCE. The sacred chickens refused to eat at the appointed time, and the angry consul, Claudius Pulcher, threw the chickens overboard with an exasperated “Well, if they don’t eat, let them drink!”
He suffered a catastrophic defeat, which was supposedly because he hadn’t taken the auspices properly.
The other type of auspicium is the auspicia oblativa. These were mostly things called prodigies, and that doesn’t mean the gifted child that can play Mozart by the age of 3. These prodigies were bad omens, and were said to be the manifestation of the wrath of the gods. These included typical things like epidemics and defeats in battle, and not so typical things like “the shrinking of the sun, the spontaneous combustion of weapons, two moons seen in the sky during the day, red-hot stones raining down from the sky, bloody sweat forming on statues, and sheep turning into goats”, as written by Livy.