Hive Sight is an innate passive ability possessed by all Kharaa lifeforms. It allows players to sense ally and enemy presence when nearby, causing them to appear as orange outlines even through walls. Kharaa players can constantly see each other, which allows them to coordinate attacks and positioning. Marines will appear for 8 seconds on Hive Sight when damaged by a Kharaa player directly. The Skulk's Parasite can reveal Marines for a longer period of time.
Hive Sight also serves as the Kharaa announcer, informing players with audio cues when friendly units and structures are under attack, as well as declaring when a Hive is dropped, completed, or killed. Hive Sight will also be responsible for conveying Alien Commander orders in the form of Pheromones, signifying where the Alien commander wishes the Kharaa team to go or attack.
It is clear that the Kharaa are linked to one another. When a hive is attacked, nearby aliens rush to the defense. When one alien engages marines, others often choose to assist. And yet, the Kharaa do not act as one – they are fiercely individual. This, and other evidence, has lead Frontiersmen scientists to speculate that instead of a "hive mind", the aliens have "hive sight".
There is documentary evidence that the aliens seem to be responding to visual cues instead of some kind of telepathy. For instance, when an enemy is on the other side of a wall, they swivel their heads as if they can see them. When a hive is attacked, they look around wildly until they find the direction of the threatened area, then run in that direction. Speculation is that the aliens have a kind of interface with the bacterium, that uses their senses to convey information. Probably through audible cues, and their own organic version of a HUD (Heads Up Display).
If all hives are destroyed, hive sight will slowly fade away over a period of around twenty hours - not quickly enough to impact battles with Frontiersmen, which are usually resolved much faster than that.