This was certainly an interesting article but it failed to recognise one simple fact.

The study did find that louder whistles can be heard at greater distances.

But the study failed to take into account that louder whistles take more effort by the person producing the puff to make that louder sound.

In a search, the person blowing the whistle will tire more quickly whilst blowing the louder whistle than the quieter one hence reducing the probability of a search party hearing the whistle. This was not factored into the results.