My sense was that this interpretation of work on the “behavioral sink” is quite off. I think most reasonable biologists and ecologists would agree that density-dependent stress tends to cause the pathologies of the type that are described in Calhoun’s work.

The fact that there are occasional sparse zones in the pen is relevant insofar as it usually implied strong individuals excluding access to those parts of the pen; it’s not a very strong argument against crowding as a chief mechanism for the sink.

That said, there is probably something interesting going on right now with regard to density and abnormal behavior - I’m just not sure that falling birth rates will exacerbate that.