Effects of environmental heterogeneity on the population dynamics of a
threatened bird endemic to subtropical salt marshes
Abstract
Understanding how environmental factors affect population dynamics is
crucial for conservation. In this study, we examine the importance of
habitat and climate factors on juvenile productivity, adult mortality,
and demographic performance (DP) of Formicivora acutirostris in a
floristic gradient (upstream and downstream) in the Guaratuba Bay
estuary, Brazil. We monitored 14–41 territories during 18 years, which
totaled 214 adult territorial individuals and 297 independent juveniles.
Data imputation, generalized linear mixed models, and random forest
models were used in the analysis. The average annual juvenile
productivity per territory was 0.64 upstream and 0.56 downstream.
Juvenile productivity upstream was positively associated with the number
of neighbors, Cladietum area, and vegetation density in Crinetum, and
showed a quadratic relationship with Acrostichetum density. Downstream,
productivity increased with precipitation and rainy days but decreased
with maximum temperature; and was higher in areas with forks in
Acrostichetum. Adult mortality averaged 0.32 upstream and 0.25
downstream. Upstream, mortality decreased with maximal tidal height,
increased with the number of rainy days, and showed a quadratic
relationship with vegetation density in Crinetum. The overall DP
upstream was 0, and downstream was 1.5. DP was positively influenced by
Cladietum area upstream and by the presence of forks in Acrostichetum
downstream. The study highlights Cladietum’s critical role in
productivity, offering safe nesting sites. Acrostichetum, beneficial
when forks are present, also provides predator refuge, impacting
productivity. Crinetum contributes minimally due to predation and
flooding. Climatic and tidal factors further influence vulnerability. We
discuss population dynamics and the importance of conservation
prioritization.