Research Training Program

Jarod Raithel
Texas A&M University
College Station , TX

Helen James, Ph.D.
Supervising Scientist
Department of Birds

"While the RTP experience provided invaluable insight into the holistic research process, working with the the moa-nalo birds imparted in me a true admiration for the wondrous evolutionary potential of life"

The collective term moa-nalo (Anatidae: Thambetochen, Ptaiochen, Chelychelynechen) translates as lost, vanished, or forgotten fowl and refers to an assemblage of massive, flightless birds that became extinct prehistorically in the Hawaiian Islands. Although evolutionarily close to dabbling ducks, since colonization they had evolved in the islands to become important terrestrial herbivores, feeding mainly on leafy vegetation in a wide range of habitats. We analyzed 16 skeletal measurements from the bill and hindlimb of two species of moa-nalos to determine whether this remarkable transformation was accompanied by a change in sexual size dimorphism. Sample distributions and their respective coefficients of variation for measurements were compared with simulated random normal distributions. Varying the mean male-to-female size ratios in the simulation allowed us to determine a plausible range of sexual size dimorphism for each measurement which best fit our observed distributions. Probable body weight estimates were calculated from simulated means of femur least shaft circumference in combination with published regression equations. Within-locality sample distributions compared among fossil localities revealed minimal confounding effects from geographic variation. To examine trends in sexual dimorphism from an evolutionary perspective, we compared our estimates of mean male-to-female ratios to expected ancestral ratios, as reconstructed from a published phylogeny of waterfowl. We conclude that there was an evolutionary increase in sexual size dimorphism in the moa-nalos, but the extent was not as extreme as in other flightless, terrestrial, insular birds such as the Solitaire of the Mascarene Islands or the New Zealand Kakapo.