Avian growth modeling: past, present and future

QUINTANA, F.; SVAGELJ, W. S.

Puerto Iguazú, Misiones

Congreso; I Ornithological Congress of the Americas; 2017

Aves Argentinas/Association of Field Ornithologists/CBO

Avian growth is an important life-history trait that varies widely at inter- and intraspecific levels. In the last fifty years, the quantitative study of avian growth has benefited mainly from the use of three mathematical growth models namely logistic, Gompertz, and von Bertalanffy. These nonlinear models were traditionally used because can be parameterized in a simple way with just three parameters with biological meaning - estimated adult size, growth rate and age at maximum growth. Despite of that, all of them have unrealistic fixed forms with inflection points fixed at a given relative value. On the other hand, violations of statistical independence among data derived from repeated measures on chicks and nests were traditionally remedied with suboptimal approaches, losing variability, data and ultimately, effort. Nowadays, nonlinear mixed effect models deal with any lack of statistical independence. Moreover, these models allow the simultaneous inclusion of growth parameters as fixed effects, describing the average growth curve and the influence of predictor variables, as well as random effects allowing for random individual variation around the average values. Also, in contraposition to traditionally used models, the Richards growth model emerged as a very attractive four-parameter alternative because it does not have a fixed form and the inflection point can vary freely. The application of nonlinear mixed effect models to the Richards equation represents a flexible and powerful analytical tool that remains almost unused by ornithologists. Here, by modeling chick growth in Imperial Cormorants (Phalacrocorax atriceps), we demonstrate several benefits derived from this innovative approach.