Famine

Famine is a gold skull featured in every Halo game to feature skulls excluding Halo Wars. Its function has remained more-or-less the same across all its appearances, aside from very minor differences.

Halo: Combat Evolved Anniversary
The skull is located on The Silent Cartographer. Once you land on the beach, turn around and walk until you see a mesa with a winding path up to the top. It is under the structure containing the security control room where the crashed Pelican appears later. The skull is at the very top and on the farthest edge of the mesa. It is surrounded by three bushes.

Famine Skull location video here

Halo 2
The skull can be found on The Oracle. After you get off of the slowly descending elevator, you will come to a hallway where you see a handful of dead bodies. Continue into the next room, and you will be on the second floor of a room that has a lot of glass windows. When you enter this room, look to the right, and find the third pane of glass. It should be to the right of a wall that has some Flood guts splattered on it. Shoot out this window, and the windows directly across the room. If you look below you, you will see a platform that has four tall posts. On the far side of the room there is a column that is right in between the two windows on the far side of the room. Turn on your Active camouflage, and jump to the center platform. Jump on either of the posts on the far side of the platform and jump to the column between the windows. Make another jump through the window you shot out, and make a left. Walk all the way to the end and you'll find four Elite Combat Forms convulsing on the floor, with the Famine Skull in the middle of them. Sometimes, the Combat Form nearest to the battlefield stands up, but it does not attack.

Halo 3

 * 1) At the point where you are directed into a fork in the road, go straight, which leads you to a giant bowl-like valley.
 * 2) Go to the right and drive directly ahead until you hit the rock wall.
 * 3) When you get underneath the platform structure, you will notice some climbable rocks on the right that will lead you to the platform itself. Climb up them.
 * 4) You will notice several beam-like supports alongside the platform. Go to the very last one at the end of the platform. If you jump up, you can see the skull at the end.
 * 5) Align yourself right up to the support. You need to get to the crevice of it, sticking out and away from the platform. There are several methods to obtain this skull:
 * Stick a Plasma Grenade right where the beam-like support and incline meet (on the bottom edge of the incline). Back up, run and jump, aiming a little higher than the skull. You should be just over and a little forward of the grenade when it explodes giving you enough of a boost to reach the skull.
 * Pick up a Deployable Cover and place it in front of the pillar with the skull and use it as a step to the ledge. It may take a few tries to place it exactly at the perfect spot, as it may slide off and fall off the ledge. The best way to do this is stand back and then take a run towards the skull and then jump whilst pulling slightly right.
 * In cooperative mode, stand on your friend's head and have them run and jump towards the skull. At the highest point of their jump, jump over to the ledge. If performed correctly, you should land on the platform.
 * Deploy a Bubble Shield so that the edge of it is near the edge of the structure and use a grenade jump to reach the skull. The Bubble Shield will keep the grenade you throw inside it. Jump right after you throw and the grenade should give you a sufficient boost.
 * Take a Brute Shot and aim it downward but still on the building. Take a leap, and as you jump, fire downward and you will be able to launch yourself to the skull.
 * If you saved the Rocket Launcher from the downed Pelican, you can rocket jump by positioning yourself a suitable running distance from the platform with the skull, running at it backward, jumping as you reach the slanted floor and firing a rocket. The blast should be sufficient to propel you to the platform. In order to do this without killing yourself, do it on Normal and with an Overshield obtained by using the Black Eye Skull.
 * Find a few Ghosts and use the boulder and a boost/A-button combo to get them onto the platform. Then stack them near the spot with the skull and you should be able to jump from on top of them to the skull.
 * On the way back through this canyon, after getting the Scorpions from the Forward Unto Dawn, as you pass under the arch and blow up the Phantom, there is a wall to the left of the part where the canyon narrows that you can drive a tank up. If you drive one up, then wedge it in the area where the Forerunner structure comes closest to the cliff you're on, you can take a second tank up the cliff and drive it across the bridge made from the first one onto the Forerunner structure. Then, with some careful positioning, use its turret as a platform to jump to the skull.
 * Follow Johnson's Pelican to the landing site. Before you go through the rock tunnel to confront the Wraith, destroy the Covenant troops near the Chopper. Take the Chopper and ride it up the ridge with the boost. Similar to the Ghost method, leap the chopper onto the ledge from the mountain range with the boost and roll it to the pylon with the skull on it. Put the Chopper as close as you can to the pylon and slowly roll it forward until the big wheel is at the edge. Get out of the Chopper, jump on the wheel, and then jump up to get the skull.

Effect
The effect of Famine is the same across all of the games: it reduces the ammunition of weapons picked up from the floor by half. This applies to weapons dropped by killed enemies and allies, and those scripted to spawn on the floor (except in Halo 2). Weapons that spawn in crates are unaffected. In addition, the skull oddly doesn't affect the M6 "Spartan Laser" G/GNR in Halo: Reach.