Direct and Indirect Factors on Bird Nestling Growth: a Case Study of the Red-Crested Cardinal using Structural Equation Models

PALACIO, FACUNDO X.; SEGURA, LUCIANO N.

San Juan, Puerto Rico

Congreso; VII North American Ornithological Conference; 2020

Nestling growth is a key life-history trait in birds, as itdetermines future individual survival and reproduction.However, how multiple spatial and temporal factors operateboth directly and indirectly on this trait remainsstill 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 duringthree breeding seasons (128 nests and 278 nestlings).We estimated growth (tarsus length and body mass) parametersper nestling from nonlinear mixed models andexplored different a priori hypotheses between growthand predictors based on biological knowledge usingstructural equation models (SEMs). Hatching order andbotfly presence had direct negative effects on the upperasymptote and growth rate, whereas the number of siblingsand time of breeding had a positive effect on bothgrowth parameters. Time of breeding also had a directeffect on botfly presence, indicating an indirect negativeeffect of this predictor on nestling growth. Finally,continuous patches had a positive effect on botfly presence,indicating a negative indirect effect of continuouspatches on nestling growth. Our results show that differentenvironmental and temporal factors drive directlyand indirectly nestling growth. As indirect ecologicaleffects are widespread in nature, the dissection of directand indirect relationships among variables would be apromising avenue to more comprehensively understandnestling growth in birds.