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For a similar sensor area, higher pixel density will give you more resolution than lower pixel density.
Anders, that is a tautologu of sorts, similar to saying that once you offload 40 people from a city bus and jam them into a VW Beetle, the latter will carry more passengers per engine displacement. That is a simple physical fact that shouldn't need a debate.
However, what is objectionable is an attempt to equate sensor pixel density with camera effectiveness for wildlife photography. The link between the two is tenuous at best, sometimes even non-existent, depending on the camera as well as wildlife type considered, and it neglects the bigger picture, operating complexities as well as aesthetics of photography.
In my view, that "pixel per duck" thing is similarly flawed to yet another birder forum doctrine which says that one can never have enough FL, yet some of the best craft practitioners shoot proximity shots with only 400mm lenses, and keep serving such images to us almost daily.
In fact, any sort of a narrow prescriptive doctrine can not be very helpful to those who are trying to enter into the craft. Several years ago a fellow from an Asian country posted on FM N&W board a series of bird shots he had taken with his Sony (?) P&S camera. Those shots I thought were very striking and beautiful, and that was not because his camera had a prodigeous sensor pixel density, but because the man must have been gifted with creative vision, and he showed considerable originality and skill in his craft.