Local extinctions exceed colonization rates in a bird community during dry years in the Brazilian Caatinga

Abstract

Droughts typically result in a widespread decline in many vertebrate populations and even the local extinction of some species. However, different species vary considerably in their resistance to the effects of drought. This study aimed to estimate the relative species richness and the colonization and extinction rates in a bird community during an acute drought event in the Brazilian Caatinga. We mist-netted birds during 3 years throughout seven field seasons in two sampling plots to estimate community parameters using multi-season dynamic occupancy models. The relative richness to the regional species pool varied considerably during the study period (16-49%) with markedly low values in the severe onset of the drought. The estimates in the savanna were higher than those in the shrubby-woodland plot (~42 vs~31 species, respectively). Pollinators and seed dispersers were characterized by median to high colonization (30-69%) and local extinction rates (37-69%), indicating low site fidelity. By contrast, granivores and insectivores made up the resident component of the community, with low local extinction and colonization rates (< 30%). Our results indicate that the diversity of Caatinga bird assemblages may decline markedly during severe droughts, primarily as a result of the displacement of species that exploit resources whose availability decreases drastically in abnormally dry years. Considering the climate scenarios predicted for tropical arid and semiarid regions worldwide, we believe that pollinators and seed dispersers will be especially vulnerable to population decline and local extinctions, which will alter community structure and the persistence of ecosystem services.

Recent population size of Timor Friarbird and resources utilization at three landscapes in West Timor Island, Indonesia

“…In the landscape, nomadic birds seek the availability of the most favorable suitable habitat conditions, able to return to the same breeding region or move to another location [54]. Semi-arid tropical environments also typically experience supra-annual cycles of intense drought [55,56]. Rainfall is a key factor for wildlife, especially nectar bird groups in semi-arid environments.…”

“…The common Friarbird population encounter is concentrated in certain areas, such as forest edge areas that have local productivity. It thus has a major impact on animal populations that depend on local productivity, changing demographic patterns, such as migration rates and deaths [13,56,66]. Knowledge of the distribution of nectar bird species such as the Timor Friarbird, which relies heavily on the availability of water resources from flowers, fruits, and insects in the semi-arid region, can help conservation activities of this target species in the future.…”

Multi-temporal ecological niche modeling for bird conservation in the face of climate change scenarios in Caatinga, Brazil

“…They are considered critical organisms for maintaining ecological balance due to their ability to disperse seeds ( Viana et al, 2016 ; Pauw , 2019 ; González-Varo et al, 2021 ), insect population control and pollination ( Whelan, Wenny & Marquis, 2008 ). Currently, Caatinga birds already suffer from the severe effects during years of intense drought, with increased vulnerability, population declines and even local extinctions, mainly of pollinators ( Toledo-Lima & Pichorim, 2020 ). Thus, this group is an excellent model for understanding the effects of future climate change.…”