Fig. 5.
Exposure of southern Kalahari birds to conditions associated with chronic, sublethal fitness costs will increase greatly during the 21st century via increases in the average number of consecutive days per year on which maximum air temperature exceeds species-specific threshold values. Past (1060–1070 CE), present (2000–2010 CE), and future (2080–2090 CE) exposures are shown as green, blue, and red, respectively. Error bars for Southern Pied Babblers and Southern Yellow-billed Hornbills show the range associated with 95% confidence intervals (CI) calculated for relationships between daily percentage of body mass gain or heat dissipation behavior and daily maximum air temperature (Tmax). In each case, the upward error bar corresponds with the Tmax value for the lower (cooler) 95% CI and the downward bar with the upper (warmer) 95% CI (in the case of zero daytime mass gain for babblers, estimating the Tmax for the upper 95% CI would require extrapolation and is hence not plotted). For Southern Fiscals, the upper bound of the error bar signifies 92.5% confidence of a negative effect of cumulative days above the threshold Tmax, and the lower bound signifies 97.5% confidence of a negative effect of cumulative days above the threshold Tmax. In the case of reduced tarsus length among the fiscals, strong nonlinearity of the effect of Tmax resulted in 92.5, 95, and 97.5% confidence in a negative effect of high Tmax being reached at ∼36.8 °C—hence the lack of visible error bars.