Keep in mind that both SMB and LMB (to a lesser degree) are thigmortophic for a reason.



The nest-building urge in males is thigmotrophic. Given a choice, they will build nests that are protected on one or more sides by "things" - logs, rocks, pilings, stumps, ledges, etc. This may provide partial protection from predators and egg robbers, or a break from wind or water current.