Long-term monitoring reveals widespread and severe declines of understory birds in a protected Neotropical forest

Abstract

Significance We leveraged a 44-y population study of Neotropical understory birds from a protected forest reserve in central Panama to document widespread and severe declines in bird abundance. Our findings provide evidence that tropical bird populations may be undergoing systematic declines, even in relatively intact forests. The implications of these findings are that biodiversity baselines may be shifting over time, and large tracts of tropical forest may not be sufficient for maintaining stable bird populations. Our study highlights the importance of long-term monitoring for detecting cryptic losses in biodiversity and motivates the need for future work drilling down to the underlying mechanisms to understand and mitigate future declines.

Species-level drivers of avian centrality within seed-dispersal networks across different levels of organization

“…Bird species are facing a long-term decline due to habitat loss and fragmentation 58 . Several species are being replaced by invasive non-native species that may not necessarily replace ecological functions 50 .…”

Wet and dry extremes reduce arthropod biomass independently of leaf phenology in the wet tropics

“…In Costa Rica, 22‐year declines in caterpillar and parasitoid richness were linked to increasing temperature and rainfall anomalies (Salcido et al, 2020 ) although moth populations in Ecuador appear stable (Wagner et al, 2021 ). Tropical birds have received greater study, and 40 years of data from Panamanian rainforest show dry season length drives demographic variability (Brawn et al, 2017 ), while a number of studies have documented enigmatic declines in undisturbed tropical rainforest, especially for understory or terrestrial insectivores likely linked to climate change (Blake & Loiselle, 2015 ; Curtis et al, 2021 ; Pollock et al, 2022 ; Sigel et al, 2006 ; Stouffer et al, 2021 ).…”

Low species turnover of upland Amazonian birds in the absence of physical barriers

“…Specific anthropogenic habitats like secondary forests or urban environments are of course treated as distinct from natural vegetation classes. However, in seemingly undisturbed forests, recent long‐term studies of birds have detected the kinds of community change normally associated with anthropogenic disturbance and have largely attributed these changes to indirect human influences (Blake & Loiselle, 2015; Pollock et al, 2022; Stouffer et al, 2021). For example, at two Amazonian sites, terrestrial and near‐ground insectivores displayed the most pronounced declines (Blake & Loiselle, 2015; Stouffer et al, 2021), whereas losses were much more widespread among Panamanian birds (Pollock et al, 2022).…”

“…However, in seemingly undisturbed forests, recent long‐term studies of birds have detected the kinds of community change normally associated with anthropogenic disturbance and have largely attributed these changes to indirect human influences (Blake & Loiselle, 2015; Pollock et al, 2022; Stouffer et al, 2021). For example, at two Amazonian sites, terrestrial and near‐ground insectivores displayed the most pronounced declines (Blake & Loiselle, 2015; Stouffer et al, 2021), whereas losses were much more widespread among Panamanian birds (Pollock et al, 2022). Thus, for temporal snapshots, incorporating anthropogenic effects at a landscape scale could help to explain local community differences.…”