Your article examines an interesting point about the role of sentinels. However, if nest predation of incubating females is extremely low, it seems difficult to support your premise. Also, how similar is the reaction of sentinels to humans as it is to potential nest predators? Do you have any evidence that birds respond to potential predators in the same way as they do to people? That is, are people the appropriate experimental model? Also, you did not describe the behavior the putative sentinel carried out to warn the incubating bird. Vocalization? Movement? Finally, you mentioned that the incubating bird did not necessarily see the approaching human, but you also stated that the nest is somewhat flimsy and I would suspect that the birds can see through the nest.