Long‐term change in the avifauna of undisturbed Amazonian rainforest: ground‐foraging birds disappear and the baseline shifts

Abstract

How are rainforest birds faring in the Anthropocene? We use bird captures spanning > 35 years from 55 sites within a vast area of intact Amazonian rainforest to reveal reduced abundance of terrestrial and near‐ground insectivores in the absence of deforestation, edge effects or other direct anthropogenic landscape change. Because undisturbed forest includes far fewer terrestrial and near‐ground insectivores than it did historically, today’s fragments and second growth are more impoverished than shown by comparisons with modern ‘control’ sites. Any goals for bird community recovery in Amazonian second growth should recognise that a modern bird community will inevitably differ from a baseline from > 35 years ago. Abundance patterns driven by landscape change may be the most conspicuous manifestation of human activity, but biodiversity declines in undisturbed forest represent hidden losses, possibly driven by climate change, that may be pervasive in intact Amazonian forests and other systems considered to be undisturbed.

Temperature‐associated decreases in demographic rates of Afrotropical bird species over 30 years

“…However, we believe that, based on the species traits of the more common temperature‐sensitive species in the Usambara understory bird community, temperature‐associated declines have very likely also occurred among many of the rarer species in this same community as well as among many of the common and uncommon understory bird species occurring in other nearby Eastern Arc Mountains (see Figure 1, Newmark & McNeally, 2018) that share similar bird communities. Elsewhere in the tropics, there is evidence that recent climate change has contributed to community‐wide declines of bird species in lowland (Blake & Loiselle, 2015; Lister & Garcia, 2018; Stouffer et al, 2020) and in other montane communities (Latta et al, 2011), to elevational range contractions (Neate‐Clegg et al, 2020), and to mountaintop extinctions (Freeman, Scholer, et al, 2018).…”

“…Such studies are important because of the unusually high diversity and endemism in the tropics and particularly in montane communities (Orme et al, 2005; Rahbek et al, 2019) where the threat of climate change is believed to be particularly great (Şekercioğlu et al, 2008). An understanding of the demographic responses of tropical birds to climate change is also central to assessing population viability, evaluating recent observed declines in tropical bird abundance (Blake & Loiselle, 2015; Latta et al, 2011; Lister & Garcia, 2018; Stouffer et al, 2020), and developing effective conservation interventions (Brawn et al, 2017).…”

“…In both high and low latitudes, temperature has been shown to be an important driver of the demographic rates of birds (Doyle et al, 2020; Dybala et al, 2013; Santisteban et al, 2012; Woodworth et al, 2018). While the magnitude of global warming—0.18°C per decade (NOAA, 2019)—has been comparatively small relative to the range of temperatures that most tropical birds typically experience over a lifetime, a year, or even a day, the impact of rapid change in mean annual temperature over the last half‐century has, nonetheless, had marked effects on the distributions (Freeman, Lee‐Yaw, et al, 2018; Freeman, Scholer, et al, 2018; Neate‐Clegg et al, 2020), community structure (Blake & Loiselle, 2015; Latta et al, 2011; Stouffer et al, 2020), and demographic rates (Srinivasan & Wilcove, 2020; Woodworth et al, 2018) of tropical birds. Most of these documented responses of tropical birds to global warming are almost certainly a result of temperature‐induced changes in biotic interactions (Lister & Garcia, 2018; Santisteban et al, 2012) such as fruiting phenology (Chapman et al, 2005), prey availability (Lister & Garcia, 2018), or predator activity (Cox et al, 2013) rather than temperature per se (Londoño et al, 2017).…”

Seasonal dynamics of flock interaction networks across a human‐modified landscape in lowland Amazonian rain forest

“…5a). Therefore, in the absence of sampling data across a full annual cycle, we recommend standardizing effort by season (e.g., Wolfe et al 2015 b , Pollock et al 2017, Rutt et al 2020; Stouffer et al 2020).…”

“…Altogether, these changes indicate that there is a characteristic rhythm to the seasons even in relatively stable lowland rain forest. Even so, most studies in the humid tropics either restrict sampling effort to a single season (Pollock et al 2017; Rutt et al 2019; Stouffer et al 2020) or ignore seasonality altogether. Furthermore, disturbance can impair the ability of forests to buffer against natural climatic variation (Ewers and Banks‐Leite 2013, González del Pliego et al 2016, Senior et al 2017), leaving human‐modified habitats more susceptible to the effects of seasonality.…”