There are some clips on Discovery.com that elaborate and put visuals to what Krech speaks about in The Ecological Indian on page 33 about megafauna.
The first few clips describe the history of humans and hunting. The clip on Maori and Megabirds talks about how the birds did not fear humans making it easier to hunt them. This can be related to Krech on page 35, " ...men (and women) arrived in the New World with knowledge of hunting large animals, but thus did not fear them, and so hunters left megafaunal extinctions in the wake." Humans were taking advantage of the animals with their hunting skills. Also the last of all the clips gives some thoughts on how Land of Lost Monters thinks the megafauna went extinct in different continents.
This next link shows what it would have been like for the humans and the megabeast to encounter each other for the first time. (They are a little intense)
I am just happy there are no megafaunas after me for lunch.