Я это так поняла.

Инкубатор для яиц и инкубатор для птенцов.

http://nvdls.unl.edu/vnewslet/PoultryFall2000.pdf

When you want to incubate eggs continuously, you need at least two incubators, one for incubation until the time of pipping and another to transfer eggs into when they are about three days from hatching. Never have eggs hatching in an incubator which also contains eggs that require more days or weeks of incubation time. This is one of the worst errors that can be made in terms of
sanitation. Transfer the eggs from the incubator (setter) to a separate hatching incubator (hatcher) about the time the first egg pips. Pipping and hatching eggs provide conditions for very rapid microbial growth, and it is best to have this occur in the hatcher. Always set and hatch eggs in clean and sanitized incubators.

Стр. 6.

Кстати, на стр. 7 очень веселый рисунок.