Same dimensions for XL birds? I have some Light Brahmas and Black Jersey Giants coming... Thanks!
You can try a ripped down 2 x 4....making it 1.5" x 1.75"......narrow side up to start......and if that seems to cause trouble, turn it to the wide side up. With the narrow side up, it is a vertical rectangular stud so to speak and will support their weight better without sagging. All mine are currently 1.5" x 1.75" narrow side up....ripped down from a 2 x 4 stud which came with edges eased over.
BTW, I checked the other evening and while on the roost, all my birds had their front toes over the front and all also had the back toe bent over the back edge. They were locked on....and crouched down. I did not check to see if their keel bones were resting on the roost bar. Studies say they do.
The only benefit I can see for the wider perches is if the birds do prefer to rest their keel bones on the wider perch.....but are forced to balance themselves to stay put if they do. Can't lock down to a wide perch. Few if any studies I have seen have included the wide perches.....like a 2 x 4 wide side up.....in the studies. I think someone on BYC did a lay study a year or so back. I don't remember what he concluded.
First "scientific" information on laying hen roost bars I can recall finding dates back over 100 years to information published by the Missouri Poultry Research Center at Mountain Grove.....circa 1915. Back then, ideal roost bars were considered to be a 1" x 2" roost.....narrow side up. But they were using smaller leghorns almost exclusively, so a smaller bird.
Other things they figured out 100 years ago was to make all roost bars on one level (no ladders) as all birds will make for the top level and will fight to get there. Far better to put them on one level and about 8" to 10" per bird spacing minimum. I currently have 2 - 8' roost bars.....16 linear feet for 23 birds, and there are generally gaps remaining.....most pack in tight to the sides......front and back....and both sides. Open real estate is in the middle. Easter eggers are always up first.....always....maybe 10 minutes or more before anyone else. They get the prime real estate on the ends.
Roosts should be higher than any other structure......like nest boxes, etc. Mine are about 40 inches off the deck and about 12 to 14 inches headroom left to the roof......10 inches off the back wall and out of drafts.....and about 14 to 15 inches apart. I have one Wyandotte who prefers to roost by herself on one of the monitor window sills.......only 3 1/2" wide. Part hangs out in space. Can't tell if she likes the greater height or solitude. Nobody is beating her up up there.
How high would they go? Given a choice.......pretty high. We were in Key West a few years back and the feral chickens there routinely work their way to 20 feet or more up in the trees. Others will roost up in the rafters of barns, etc.