Effects of livestock grazing on flocks of seed-eating birds in the central Monte desert, Argentina

Abstract

Animal populations often decline due to habitat disturbance, but the initial response of organisms to human-induced environmental change is usually behavioral. Intra- and inter-specific interactions can restrict or facilitate access to resources, resulting in changes to individual fitness, and resource depletion may affect the frequency and strength of interactions. In birds, it is often assumed that feeding in groups increases foraging efficiency. We assessed how the reduction of seed resources provoked by cattle grazing affected different properties of seed-eating bird flocks in woodlands having the same structural characteristics but differing in seed abundance. Under lower availability of grass seeds (i.e., under grazing), flocks were smaller and less rich and birds showed a lower flocking propensity. This pattern could be explained by three non-exclusive hypotheses. Food reduction caused by grazing (i) decreases the number of seed-eating birds and concomitantly generates smaller flocks; (ii) reduces the density of nuclear species, decreasing the group cohesion in large flocks; (iii) makes large flocks less attractive by increasing individual competence for food. Our results provide evidence that cattle grazing affect the interactions of seed-eating birds and suggest the importance of understanding flocking behavior to bring about management actions.

Plausible causes of seed preferences and diet composition in seed‐eating passerines

“…Other analytical challenges of GLMs like multicollinearity or the correct assignment of relative weights to the estimates of each independent variable included in the models could be solved, but over dispersion remained and quasi-binomial distributions produced some unsatisfactory results. Therefore, we opted for robustness as a criterion for maintaining the current analyses and outputs (Marone et al 2019). The main results of the GLMs with binomial distribution were consistent with those of simple correlation analyses (Supporting information) as well as multiple regression analyses.…”

“…At the same time, such preferences can explain the pervasive bottom-up effect provoked by the reduction of large seeds under continuous cattle grazing on both the behaviour (i.e. diet switching; Marone et al 2017) and the abundance of seed-eating birds in the central Monte desert (Zarco et al 2019, Sagario et al 2020).…”

Estructura y composición de las bandadas mixtas de aves invernales a lo largo del gradiente latitudinal en las selvas montanas de las Yungas, Argentina

“…Estudios previos, evidenciaron que la variación en la estructura y composición de las bandadas mixtas puede deberse a diferentes factores, tanto locales como regionales, como los diferentes gradientes donde se desplacen (por ejemplo, gradientes altitudinales), las características locales de la vegetación, las condiciones de conservación de un paisaje o las condiciones climáticas locales (Mokross et al, 2014;Goodale et al, 2015;Kajiki. et al, 2018;Zarco et al 2019;Montaño-Centellas, 2020;Jones, Walters, Robinson, 2021;Montaño-Centellas y Jones, 2021).…”