Why do they fight for position?

This is the best description of the pecking order I've ever found:
In any flock of chickens there are birds who peck at other flock members and birds who submit to other flock members. This order creates a hierarchical chain in which each chicken has a place. The rank of the chicken is dependant upon whom he pecks at and whom he submits to. He ranks lower than those he submits to and higher than those who he pecks at. A flock of chicks generally has their pecking order up and running by the time they're five to seven weeks old.
Pullets and cockerels maintain seperate pecking orders within the same flock, as do hens and adult roosters. Hens automatically accept higher-ranking roosters as superiors, but dominant hens give low-ranking cocks and uppity young cockerels a very hard time.
In a closed flock with an established pecking order, there is very little infighting. Each chicken knows his or her place, and except among some roosters there is suprisingly little jostling for position. Dominant chickens signal their superiority by raising their heads and tails and glaring at subordinates, who submit by crouching, tilting their heads to one side, and gazing away - or beat a hasty retreat.
The addition of a single newcomer or removal of a high-ranking cock or hen upsets the hierachy and great deal of mayhem erupts until a new pecking order evolves. Since brawls are invariably stressful, it's unwise to move birds from coop to coop.
Because low-ranking chickens are shushed away from feed and water by bossier birds, they rarely grow or lay as well as the rest. Indeed, low-ranking individuals sometimes starve. If pecked by their betters until they bleed, they may be cannibalized by the rest of the flock. It's important to provide enough floor space, feeders, and waterers so underlings can avoid kingpins and survive.
* Hobby Farms Chickens - Tending a Small-Scale Flock for Pleasure and Profit.

 

If you have a rooster you will notice that the top hens get to sleep next to him

 

Quote:That is so true

 

Quote:That was very interesting! I've been worried (like the original poster) about how nasty the girls have been at "bedtime". I even went so far as to double the space of the top roost lol. It has slightly improved relations, there is room now for underlings to get out of the way of the meanest girls!

 

We have 5 four-foot step roosts. Ten, sometimes eleven, of them get on the top one with the others on the next one down. If I forget and leave the end window halfway open (it swings in), Ruby roosts on top of it! These are 14 week-old pullets and one cockeral crowding onto two roosts. When it's hot, they're panting their little brains off, and I'm telling them if they'd just spread out a little. Silly chickens!

For those of you about to yell at me about keeping the coop cool, I have two large windows open with a fan bringing in cool air from outside (not blowing directly on the chickens).