I'm curious what do you suspect is stopping them at 'necessary' and not allowing them to continue to 'ideal' when the water is fully available for them to consume as much as they desire anytime they desire?
I think 'work' is a little exaggerated in this instance, one could easily argue it's also stimulating activity that removes boredom and has a positive effect, must like a suet or seed block does vs a bowl of crumbles they can gorge on rapidly...
Pecking is a natural motion, chicken peck for food and they will peck for water droplets on surfaces as well... Sure they might normally drink from open water in the wild (as would humans) but that doesn't equate to alternative methods necessarily being an unnatural motion... If one is to equate a chicken reaching upwards for a nipple to be unnatural then one could also suggest that a watering bowl that is elevated above the ground on a brick (as most people do) where the chicken has to reach upwards is also unnatural, correct? So we should all be burying our water bowls at ground level?
After reading the study (
https://ps.oxfordjournals.org/content/76/7/944.full.pdf+html ) I find much of the above speculated results to be taken out of context or a speculated expansion of what was actually determined from the study in question, surprisingly bad science for a published work...
The short of it the study did not point out that the chickens have difficulty drinking from nipples, or that they posed any negative effect I find that to be pure speculation and opinion by the authors of the study, as their own results show that in lower temps the chickens consumed more water from the nipples this is 100% contrary to their conclusion... One could agree that they had difficulty drinking from 'high' water nipples when they are panting, and thus if one is using nipples they should reduce conditions that increase panting and that the nipples should be at a lower height... The mere fact that their own data showed more consumption from nipples then the cups as the temperature decreased, invalidates their conclusion that it's difficult for them to drink from nipples, as it's totally contradicts the conclusion and points towards sloppy study and bad scientific practices...
IMO when you include the fact that the study was clear that waste was not calculated or measured at all, that fact alone mostly invalidates the study or at best makes the results factually unreliable as the entirety of the extra water they claimed was consumed could actually have been waste water that was never consumed at all... Every chicken owner knows that if you give chickens open water they will splash and waste it to not account for this in a study of water consumption is simply unbelievable...
I also have to really question why the nipple water consumption was higher in cooler temps then the 'open' water source at that same temp? To me this suggest that if the chickens actually desire a higher amount of water they are fully capable of getting it from the nipples and the nipples do not limit consumption or cause a hardship... You can't simply ignore the data that doesn't fit the proclaimed conclusion as they appear to have done with this study...
The study also never determined what the 'ideal' level of water consumption actually was or is, thus there is no way on can concluded that the chickens on the nipples were deprived of their 'ideal' amount of water at any time...
I do understand that you might not like nipples and that is fine, but I find the claim that chickens will suffer and not get the 'ideal' amount of water when using nipples to be almost entirely speculation and not based on fact...
I linked the study's full text, I personally find the study to be flawed on many levels, but anyone is free to read it and come to their own conclusions if nipples actually deprive chickens of their ideal water consumption levels...