While I know very little about pigeons and what body weight they should be keeping animals on the lean side usually increases longevity.
Read the wiki on him (yes I know and am well aware wiki is often wonky) which mentions the use of "operant conditioning" with the pigeons, and that pigeons seemed to develop rituals along the lines of what is considered "superstition" in people.
Operant conditioning is very effective in dog training, "naming" a desired action with a reward works wonders in my dogs.

PETA is a stopped clock. They've done so much damage, their followers so cult like, profiting off zealotry that they've killed any good they may espouse.
They are a money making machine yet their rehoming rate is abysmal and the actions of some of their followers are vile, cruel and criminal.
They aren't the only organization that profits off those mindsets. People need to do their homework anymore and find non profits worthy of support instead of throwing money away at these disgusting businesses.

I think you don't wanna know the half of what's involved with animal studies. Driving with a friend and his wife in the car, when she suddenly blurts out that her rabbits aren't doing well. The simple question of 'why?' produces the equally simple answer: "They're implanted with artificial hernias." Hope there was something meaningful behind that research.

As to free will..
I was listening to a podcast that was talking about modern psychology/philosophy..
One person made the case that actual free will is almost nonexistent. Past my smart level but interesting..

PETA became irrelevant pretty quickly, but the general public has become less tolerant of animal cruelty..
My view has usually been. If it will save 100's of lives, then I am generally ok with animal testing. . but for testing of stuff like makeup (when animal testing is done just because its cheaper), then no..
Starving a rat or pigeon is a bit of a grey area for me, (as some medical/behavioral research can not always be done on volunteers , nor machines)..

Being hungry is different than starving...I think we are conditioned to think in extremes when most Americans have no clue what being hungry even feels like, let alone starving...many cultures practice fasting, a form of starvation, and we do not...

I would be more concerned about how doing this affected the outcome of his behavioral studies...it appears that any animal/human would work harder to obtain food under those conditions, thus creating a variable that perhaps factored into the outcome of his studies. Nothing like setting up an experiment to force results to fit your hypothesis...

PETA has become more extreme throughout the years so I have no good opinion of them and have quit supporting their efforts, except for the whales...

Oh People Eating Tasty Animals! I stopped giving two shits about what they thought when they announced that all pit bull terriers should be eradicated.

But I do invite them to all of the cook out competitions in the lower 48 each year.?

I'm sure PETA would think what Skinner did with his pigeons was unethical, but I don't really care what PETA thinks. I don't think ethics apply to animals, but deal with what is good for one's own life and one's dealings with other humans. Regarding Skinner's behaviorism, like you said, it leaves out free will, which is crucial to human action.