In this paragraph you said: Despite their popularity, surprisingly few studies have examined survey results to offer guidelines for efficient study design (Rowcliffe et al., 2008; Tobler et al., 2008; Rovero & Marshall, 2009; but see Williams, Nichols & Conroy, 2002; MacKenzie et al., 2006).

However, the following two paragraphs, it seems that there have been lots of researchers explored this issue, although there may not be a best solution for every region and every species (actually, this is the truth in ecology).