Direct and indirect factors on bird nestling growth: a case study of the Red-crested Cardinal using structural equation models

PALACIO, FACUNDO XAVIER; SEGURA, LUCIANO N.

Congreso; VII North American Ornithological Conference; 2020

Nestling growth is a key life-history trait in birds, as it determines future individual survival and reproduction. However, how multiple spatial and temporal factors operate both directly and indirectly on this trait remains still little understood. We assessed how different factors (number of siblings, hatching order, time of breeding, isolated vs continuous forest patches, and botfly parasitism) affect nestling growth in the Red-crested Cardinal (Paroaria coronata) in east-central Argentina during three breeding seasons (128 nests and 278 nestlings). We estimated growth (tarsus length and body mass) parameters per nestling from nonlinear mixed models and explored different a priori hypotheses between growth and predictors based on biological knowledge using structural equation models (SEMs). Hatching order and botfly presence had direct negative effects on the upper asymptote and growth rate, whereas the number of siblings and time of breeding had a positive effect on both growth parameters. Time of breeding also had a direct effect on botfly presence, indicating an indirect negative effect of this predictor on nestling growth. Finally, continuous patches had a positive effect on botfly presence, indicating a negative indirect effect of continuous patches on nestling growth. Our results show that different environmental and temporal factors drive directly and indirectly nestling growth. As indirect ecological effects are widespread in nature, the dissection of direct and indirect relationships among variables would be a promising avenue to more comprehensively understand nestling growth in birds.