Jenni and Winkler 2020 cont. Chapter 4: this is on the effects of environmental conditions during moult on plumage quality.
First point of importance here is that (as of when the book was written, so up to 2020) there are no studies of this in large species that retain their primary feathers for up to 3 years, and for whom feather quality is of particular value; the studies that have been done looked at small passerines like sparrows and tits. So what follows may not be representative for galliformes in general and chickens in particular.
With that caveat in mind, main conclusion is: fast moult speed seems to have a strong negative effect on all aspects of structural feather quality (size, resistance to wear, insulation properties etc.). Some birds sometimes skip breeding entirely in a given year in order to have a good moult and restore plumage quality (rather than rush it after raising a brood) e.g. middle-sized albatrosses. The other thing they stress is that plumage quality is a product of conditions during the moult period. Those conditions have far reaching carry over effects, because that plumage has a huge impact on the bird's life for the rest of the year or three, until those feathers are replaced in a subsequent partial or full moult.
Other significant findings that caught my attention are: Food shortages in general, or lack of particular nutrients required during moult, may have one or more consequences: it may cause a delay or interruption to the moult; may lead to feather production at the expense of body reserves (drawing what's needed from other body tissues); may reduce the number of feathers grown simultaneously or the feather growth rate, thereby extending the moult; and/or it may reduce the feather quality.
The birds studied prioritized their normal moult timing and intensity at the expense of body reserves and then feather quality. Even severe malnutrition does not normally stop the onset of the process, and moult may proceed even until death by malnutrition.
NB Defects in feathers caused by particular nutrient deficiencies "are rarely observed in free-living birds", p. 153, but "in free-living birds, evidence that habitat quality or food availability affects plumage quality is scarce", p. 154.
There are 3 kinds of malformation in feathers; the terminology used for them here is (i) pale or pallid bands, (ii) fault bars, and (iii) feather holes. Pallid bands, typically a few mm wide, have reduced pigmentation, and seem to be produced by malnutrition. A fault bar, about 1mm wide, is a translucent line across the entire vane or just part of it, where the barbules are reduced or missing, and seems to be caused by acute short-term stress events such as handling, fear, or sudden cold impacting the growth in the follicle. Fault bars compromise the integrity of the vane and are typically where a feather will break. Holes are the result of bacterial decomposition or chewing lice. See attached photos for illustrations.
The term 'stress bar' is not used in the book. Regarding stress, it was pointed out in chapter 3 that a normal moult down-regulates corticosterone production; lab experiments that injected abnormally high doses of this stress hormone into birds (some of whose feathers had been plucked in order to study regrowth, so outside a normal moulting period and processes) did compromise replacement feather growth, but naturally occurring corticosterone concentrations do not interfere with feather growth or quality.
she knows you bring the food.
