Following is taken from the Predator wiki site, under culture
http://avp.wikia.com/wiki/Yautja_%28Predator%29: Culture and History
Hunting culture: Predator culture revolves around the stalking and hunting of dangerous life forms. Predators primarily hunt neither for sustenance nor elimination of threats, but purely as a means of entertainment and proof of worth. As such, they will only attack life forms that have the ability, natural or technological, to provide them with a challenge. Indeed, Predators will often travel great distances to find worthy opponents, or seek out ways in which to attract or transport such prey to them. When travelling to other locations, Predators are often drawn by intense heat and armed conflict. Predators have been known to use other non-sentient species as tools to aid them in their hunts, including alien hunting hounds. On occasion, if a particularly worthy member of a sentient species is found on a hunt, Predators will systematically eliminate those who are close to the intended target in an attempt to enrage them and increase the challenge of the final confrontation. After making a kill, a Predator will mutilate the corpse and turn it into a trophy. This can involve skinning or decapitating the carcass, or even removing all of the bones from the body altogether. One typical means of displaying a kill is to hang the flayed body upside down from a great height. Skulls and sometimes spinal cords are routinely removed and collected, and can commonly be found displayed on board Predator vessels or even worn about the Predator's person if size permits this. Despite the ferocity and brutality with which Predators hunt and kill their prey, they adhere to a strict code of honor that forbids them from killing children or unarmed adults. They have also been known to spare pregnant women and those with terminal illnesses, although they will not hesitate to kill such targets if directly attacked by them. A human who has managed to kill a Predator in single combat is often spared and even rewarded with a gift (often a rare or exotic weapon) as a sign of respect. In even rarer cases, a human who has fought valiantly alongside a Predator may be similarly honored, as was the case with Alexa Woods. Failure in a hunt typically results in the Predator committing honorable suicide, usually through the detonation of their Wrist Gauntlet's self-destruct mechanism, which may simultaneously be used as a last-ditch attempt to kill their prey. This explosion is also intended to wipe out all traces of the Predator and prevent their technology from falling into the hands of their prey, an occurrence which is considered a huge affront by Yautja society and typically results in the Predator responsible being banished. Should they be killed, a Predator's ship will return automatically to the home world, taking with it a record of the individual's hunt, recorded through their Bio-Mask.
Society: The Yautja society operates a class system, nominally based on an individual’s hunting experience and prowess. Their castes includes: Young Blood/Unblooded: About 25% of male Yautja are unblooded. This means that the Predator has made no distinguishable kills. Once a Predator kills their first worthy target, usually a Xenomorph, and collects its head as trophy, they become blooded. All unblooded are children too young to safely hunt Xenomorphs, or those who simply have not had the chance to battle a Xenomorph yet.
Blooded: About 45% of male Yautja are blooded. These are warriors who have gained their clan's symbol upon their forehead after their first successful Xenomorph hunt. They are allowed access to more advanced weaponry denied to the unblooded Predators, including the Plasma Caster.
Retirees: About 10% of male Yautja are retirees, Predators who have fought their time and now are too old and honored to hunt. Females commonly come under this section due to their roles as mothers and the driving force behind the home world’s natural wasteland systems.
Elite: Elite Predators are often leaders in their clan, and are only elevated to the caste of Elite Predator once they have acquired the skull of a Xenomorph Queen. About 15% of blooded Yautja are Elite Predators. Elites specialize in a particular weapon, making that weapon their strong suit; for example, a Brawler specializes in Wrist Blades, while a Spearmaster specializes with the Combi-Stick. Elite Predators often become retirees after a few decades.
Clan Leader: Clan Leaders are only made by the Adjudicator's decision. The only way to become a Clan Leader is to clean out an entire Xenomorph Hive larger than 300 members with a maximum of two other Predators. When this has been proven, the three (or fewer) Yautja all become Clan Leaders. They become the forefathers of that clan and will repopulate with females of their choosing. In order to be eligible for the trials of a Hive cleansing, each member of the trio must have at least 3 Queen skull trophies. After this point, any Hive cleansings that the forefathers complete will give the clan greater honor and standing in the caste system. Clan leaders comprise 5% of the Yautja society.
Adjudicators: The adjudicators are the administrators and law enforcers of the Yautja. They are world leaders and the ruling class in Predator society. Less than 1% of Yautja are adjudicators, due to their massive worldly role. At this point, they simply no longer have time to hunt off planet, but often foray into the underground hunting grounds, where younger hunters train in order to lend experience to the young ones. Adjudicators are always the leaders of a clan and no adjudicators have ever risen to that position without first having completed at least five Hive cleansings.
Bad Bloods: These are criminal Yautja who have been sentenced to death and escaped. The Predator justice system shows that crime is very low. About 2% of Yautja are bad bloods. In Predator: Concrete Jungle, the term bad bloods was also applied to Predators captured by humans and brainwashed. They met honorable deaths at the hands of their clan brother Scarface.
Apprentice: These are honorable humans taken by Predators to learn their ways.