Good news, at least so far. The 3 chicks put into a cage and given chick starter yesterday are perfectly fine today. As their combs weren't very pale and they lacked other symptoms, it's probably not all that likely they were severely affected by coccidiosis. In fact it may not have been that at all.
The remainder are all thriving and the sneezes appear to have vanished, with no signs of mucus or anything else respiratory. In fact, today they all look like normal chicks.
However late yesterday I noticed the chicks all cowering inside their shelter, and realised the resident grey goshawk has probably taken to dive-bombing. With netting stretched above the pen he can't catch the chicks, but he can certainly scare the life out of them when I'm not looking.
Today I made a 2m x 1m bamboo grid and suspended this just below the netting to make a hide in a corner of the pen. On top of the bamboo grid I laid several green bamboo cuttings that have made a nice leafy overhead screen. I also wired more leafy bamboo lengths in an upright position around the northern pen wall (which is the direction from which the goshawk cases the pen, flying low among the forest trees as he scopes through the mesh). Since these sections of bamboo are quite tall and willowy, they bend over just under the netting and form a bit of a concealing arch.
I've always cursed the neighbour's bamboo for getting out of control and covering our front yard, but I'm a bit of a convert to its usefulness. Garden stakes, pen shields, trellises, you name it — I'd never plant the invasive sort, but now it's here it can be a very useful thing.
Meanwhile I don't know about the chicks' sneezing — it's too early to tell if there's an underlying illness — but all the birds are bright and happy today. I'll keep an eye out.
It might seem a little premature to keep blogging without knowing outcomes, but I'd like to be as honest and up front as possible, in case there's any good reason to warn others off what I'm doing. After all, in the absence of a clear 'how to', this is trial and error.
But hopefully more trial than error. :-)