Multivariate skeletal analyses support a taxonomic distinction between New Zealand and Australian <i>Eudyptula</i> penguins (Sphenisciformes: Spheniscidae)

Recent genetic analyses have revealed evidence for the existence of two distinct lineages of Little Penguin (genus <i>Eudyptula</i>), one endemic to New Zealand (<i>E. minor</i>), and the other widespread along the coasts of Australia and south-east New Zealand (<i>E. novaehollandiae</i>). Here we present the first comprehensive morphometric analysis of complete <i>Eudyptula</i> skeletons. We show that variability in <i>Eudyptula</i> body and bill size is associated with sea surface temperature gradients, suggesting that thermoregulatory processes underpin morphological variation in these seabirds. More importantly, we detect osteological differentiation between New Zealand and Australian specimens, providing further support for the taxonomic separation of these behaviourally and genetically distinct lineages. Broadly, our study shows the value of multivariate osteological analyses in helping to resolve the status of genetic lineages that appear morphologically ‘cryptic’ when considering external morphometrics and plumage features alone.