Temperatures in excess of critical thresholds threaten nestling growth and survival in a rapidly-warming arid savanna: a study of common fiscals

PLoS One. 2013 Sep 9;8(9):e74613. doi: 10.1371/journal.pone.0074613. eCollection 2013.


Frequency, duration, and intensity of hot-weather events are all predicted to increase with climate warming. Despite this, mechanisms by which temperature increases affect individual fitness and drive population-level changes are poorly understood. We investigated the link between daily maximum air temperature (tmax) and breeding success of Kalahari common fiscals (Lanius collaris) in terms of the daily effect on nestling body-mass gain, and the cumulative effect on size and age of fledglings. High tmax reduced mass gain of younger, but not older nestlings and average nestling-period tmax did not affect fledgling size. Instead, the frequency with which tmax exceeded critical thresholds (tcrits) significantly reduced fledging body mass (tcrit = 33°C) and tarsus length (tcrit= 37°C), as well as delaying fledging (tcrit= 35°C). Nest failure risk was 4.2% per day therefore delays reduced fledging probability. Smaller size at fledging often correlates with reduced lifetime fitness and might also underlie documented adult body-size reductions in desert birds in relation to climate warming. Temperature thresholds above which organisms incur fitness costs are probably common, as physiological responses to temperature are non-linear. Understanding the shape of the relationship between temperature and fitness has implications for our ability to predict species' responses to climate change.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptation, Physiological
  • Animals
  • Body Size
  • Climate*
  • Female
  • Geography
  • Male
  • Models, Statistical
  • Passeriformes / growth & development*
  • Probability
  • South Africa
  • Survival Analysis
  • Temperature*
  • Video Recording

Grant support

This study was funded by a grant from the Department of Science and Technology (http://www.dst.gov.za/) through the National Research Foundation (http://www.nrf.ac.za/) of South Africa to the Centre of Excellence (CoE) in Birds as Keys to Biodiversity Conservation at the Percy FitzPatrick Institute of African Ornithology (http://www.fitzpatrick.uct.ac.za/docs/coe.html). Additional funding from the Tswalu Foundation (http://www.tswalu.com/blog/the-tswalu-foundation/) covered accommodation costs at Tswalu Kalahari Reserve. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.