Does a lack of design and repeatability compromise scientific criticism? A Response to Smith et al. (2009)

In a recent paper published in The Auk, Smith et al. (2009) raised serious concerns over an apparent lack of reproducibility in their study of stable hydrogen isotope values (δD_f ) in raptor feathers. The authors based their concerns on results obtained from different laboratories to which they submitted original and blind “repeats” over a multiyear period. A regression of the original sample δD versus “repeat” measurements showed an increase in the magnitude of residuals with increasing δD_f , especially for values greater than about −80‰ (Smith et al. 2009: fig. 2). Because of this, the authors “caution against the continued use of δD_f for predicting geographic origin, and for addressing important conservation questions” (p. 41) and conclude that “it is counterproductive to move forward [with hydrogen isotopes in avian studies] without first establishing full confidence in the technique that underlies such insights and conservation recommendations” (p. 45). We disagree with these sentiments.