After they became too big for the original cold brooder (the timber box with little door and inner mesh circlet), I did a little extra work on the design. Remember that that 600mm x 600mm box was their square nest enclosure; there was also a detachable timber-walled run, which was about 620mm x 1200mm. (You can see the original cold brooder under my 'how to' to the right.)
To make a new cold brooder, I used the old one (timber box plus run) in a new way. Basically the old timber-walled run is now the actual nesting area, and the old nesting area is now an insulated roof. In this version the insulation is mostly above the chicks rather than around the sides. (More on the nest setup later.)
If you look closely you may be able to tell that the double-storey-looking section to the far left (with a lid and weight on top) is my old box brooder on top of the old boxed run. These now abut the new run (which is hard to make out in the photo because it isn't continuously meshed on top, but has a central lift-up lid framed in old timber planks).
It looks ugly, but it cost nothing because I had mesh offcuts lying around and our old farm shed is full of planks and other pieces of timber. Some people would prefer to buy the materials and frame something nicely, but I don't mind the rough look and I do enjoy using waste material (especially hardwood).
This setup has no floor but the floor of the shed is concrete, so there's no danger of anything digging in. However because this shed also gets some run-off through it during drenching rain, I've elevated the run and the nesting area on a couple dozen planks to form a basic sort of floor. This is a possible point of vulnerability if a fox dislodges the planks, but even if it did, the unit is a little too heavy for a fox to then flip over to get at the chicks.
Now for details on the all-important nest area. In the photo below, it's the section to the right. You may be able to see that just below the box sitting on top of the lower section are tufts of hay that mark out where the nest actually is (ignore all the hay spilt on the ground below). In other words the nest area is only that square section just below the upper box.
This style of cold brooder contains all the insulation in the box above the nest, with the box meshed below so the insulation can't fall into the brooder. I've also packed a little loose hay between the insulation-holding roof box and the meshed top of what used to be the old brooder run below.
The basic principle is a three-sided timber box with a fringed curtain along the front and all insulation contained above the chicks, in the upper box. A more standard way to make this kind of cold brooder is to use a predator-proof and weather-proof shed and make the nest area out of a 4-legged box with a fringe of hessian or other fabric all around. Being all around gives better ventilation and air supply; in my version above, chicks in the back of the brooder might suffocate if the majority crowd near the fringe. To avert that I've made sure there are a few gaps around the edges where the upper box meets the lower one (the area stuffed with loose hay). I've also made sure the insulation inside the upper box (which only comes up about halfway) is very loose, allowing a degree of ventilation through it as well. Thus chicks deep inside the brooder can still breathe.
Like all cold brooders, the insulation needs to be quite close to the chicks' backs and the chicks need to be closed in at night for a while until they associate going through the curtain with getting warm (you can use a temporary board across the fringed area and take it away when the chicks need to come out; just be careful not to limit ventilation). To make sure chicks' backs are up at the insulation I add extra floor material and (as with my earlier cold brooder) take it out as they grow. A simple timber strip on the floor at the entrance (or on all entrances if you use a 4-fringed brooder) will help keep nesting material inside until it needs to be taken out.
In the photo below you may just be able to make out some of the fringed curtain that hangs across the entrance to the nest compartment.
As I've said before, you know the cold brooder is working when chicks emerge at full tilt, looking happy and active exactly as they do under a lamp. However until chicks learn to come and go from the insulated area it can be quite hard work to have to keep putting them away and letting them out again. In this case though, my chicks have learned to use the fringed brooder very quickly, perhaps helped by a few design features such as the narrow 'foyer' before the curtain.
When I say 'design feature' perhaps it's more honest to say 'accidental design feature'… It was a result of the original timber-walled run being longer than the brooding box currently being used as its lid. The fringed curtain needed to be placed directly below the rim of the upper insulated box. This left a small section of the old timber-walled run sticking out (before joining onto the wider new run). A better way to describe it might be a bit of a 'bottleneck', if that makes sense. But this narrowed area has proved a bonus because the chicks like to huddle in the 'foyer' as the day grows cool, and huddling there as a group eventually forces some of them through the curtain into the inner compartment. When they realise it's warmer inside, their happy cheeps soon draw others inside, and the chicks quickly learn that going through the curtain is a good idea.
These chicks are 2 weeks old. They've been cold brooded in the above brooder for the past 5 days entirely without extra heat and without having to be taken out and put in the nest area. I'm finding the setup very low maintenance at the moment. Funnily, the day I shifted them to being fully cold brooded (up to day 9 they had a lamp during the day) we had a lengthy blackout and a cool snap that sent temperatures down to 13C at midday, which is cool for this climate zone. It was the overcast chill that I think taught the chicks what to do better than I'd been able to. Without sunlight streaming into the run area (as it normally does) they broke the association between the run area and heat, and resorted to the cosier nestbox. Associating light with heat is a real problem for chicks reared under a lamp initially, and sunlight being generally warm can also confuse them and stop them learning to use the nest. The lack of any other option than cold brooding also stopped me from being able to switch the lamp on out of worry that they wouldn't survive. There now — a lesson all round! Chicks can learn to use a cold brooder quite capably if they're forced to do it.
Now they're using the cold brooder very well indeed — as soon as they start to feel cold, they go up near the curtain and gradually move inside. Huddling isn't the sign of danger we've been taught when raising chicks in a heated brooder. In that situation it probably would be a sign of inadequate heat generally. But huddling is an essential part of cold brooding.
Another important note about all cold brooding, but especially with high numbers of chicks, is that the nest area litter needs to be checked daily for moisture content. This is because chicks defecate on their bedding and that, combined with their respiration in such a small area, will tend to make the litter increasingly moist. This is especially a problem with meat chicks because of their high metabolism. I probably don't need to say that damp litter is not good for insulation (in an artificially heated brooder the litter tends to stay more dry). Thus about every 3 days, I open the top of the nest area by lifting off the upper box and opening the mesh door below, and I exchange mucky litter for clean dry litter. I've also put a lid on top of the upper box to help stop condensation from our shed roof from dripping into the insulating material and destroying its insulating abilities. In a dry and fully walled shed this wouldn't be an issue, but you can see the lid on the box below. Holes already drilled into the insulated roof-box (from when it was my original cold brooder nest box) mean that the litter inside should be able to vent to the open air to some degree. If this box had no vent holes in its sides, I imagine I'd have to raise the lid on a few blocks above the timber box so that the insulation material inside the box could breathe.
In the photo below you can see both the lid (with its weight to hold it down) and the narrowed 'foyer' area where chicks congregate before moving into the nest area to the left.
So there is it — a lengthy saga but hopefully more information for anyone considering how to do this themselves. I wouldn't suggest anyone cold broods without a good background in raising chicks in the first place, but at least I can say that the balance between ventilation, insulation, adaptability and chick health comes quite naturally with time.
And given the problems with service infrastructure lately — and what seems like profit-motive indifference to individuals — I'm happy to know I can brood chicks off the grid if need be.
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