Very nice information, thank you!

But personally, I'm still wondering, why people prefer to include a whistle in their survival packs instead of learning and mastering the ancient art of whistling without it? Even in the genius Doug's PSK some of the precious space is sacrificed for a whistle. I can tell you for sure, that the simplest 4-finger whistle method will outperform any small plastic whistle, being of 0 oz in weight and 0x0x0" in dimensions...

Any thoughts?