A disconnect between upslope shifts and climate change in an Afrotropical bird community

Abstract

Climate change threatens to push species to higher elevations and eventual extinction. Birds, in particular, are shown to be shifting upslope in the Neotropics and Southeast Asia. Yet previous studies have lacked the temporal resolution to investigate distributional dynamics over time in relation to climatic fluctuations, especially in the understudied Afrotropics. Here, we used 15 years of point-count data from across an elevational gradient (1,767-2,940 m) in Rwanda, to assess elevational shift rates and dynamics in a community of Afrotropical birds. In general, species shifted their elevations upslope by 1.9 m/year, especially at their lower elevational limits which shifted by 4.4 m/year. Importantly, these shifts occurred despite the fact that local temperature and precipitation showed little trend over the study period. Moreover, the interannual distributions of few species were associated with temperature, suggesting that temperature played little direct role in determining elevational distributions of birds. Instead, upslope shifts may be more related to incremental shifts in habitat and resources which lag behind decades of increased temperature in the region. Precipitation appeared to have more of an effect than temperature in determining interannual elevational changes, allowing species to expand their ranges in years of higher rainfall. Our results highlight the need to understand the mechanisms driving upslope shifts as they occur throughout the tropics. It will be critical for montane regions of the tropics to preserve contiguous blocks of forest across elevational gradients to allow wildlife to shift unimpeded.

Afrotropical montane birds experience upslope shifts and range contractions along a fragmented elevational gradient in response to global warming

“…Thus, there would appear to be few species traits that are associated with upslope shifts across species, although rigorously assessing species traits is problematic due to sample size (n = 29). These results are consistent with a lack of pattern in species traits associated with shifts observed in the Neotropics and Southeast Asia [ 13 , 25 , 26 ], although in the Albertine Rift of Rwanda shift rates in tropical birds have been associated with avian body size [ 38 ]. The association between shift rates and species traits clearly warrants further investigation across the tropics.…”

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).…”

“…Furthermore, even when the time model performed better than the temperature model, temperature cannot be ruled out as the driver behind decreases in λ . It is possible, for example, that temperature‐driven changes in habitat and resource availability accrue very slowly over time (Feeley et al, 2011) and consequently changes in demographic rates may not closely track interannual fluctuations in temperature (Neate‐Clegg et al, 2020; Srinivasan & Wilcove, 2020).…”

“…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).…”

Montane species track rising temperatures better in the tropics than in the temperate zone

“…Negative scores indicate changes in species ranges or composition that are in the “wrong” direction (e.g., downslope shifts despite warming temperatures). Because we were interested in responses to warming, we did not include three range shift studies that reported cooling temperatures when analyzing temperature tracking (Moskwik 2014; Neate - Clegg et al . 2020).…”