Author, Katherine du Plessis, with Southern Pied Babbler
The trend of global warming could prove catastrophic for warm-blooded species due to the tradeoffs between keeping cool and other necessary activities for survival such as finding food. In arid environments, where energy sources and water are already limited, small increases in temperature, which requires even more energy to combat, heighten the risk of local extinctions. Katherine L. du Plessis, affiliated with the University of Cape Town, performed a study published in the October 2012 edition of Global Change Biology, on her findings of the effects of high temperatures on foraging (searching for food), temperature regulation and body condition on a population Southern Pied Babbler birds in South Africa. The study found that the high temperatures decreased foraging efficiency and mass gain from dawn to dusk and increased the amount of time spent on eliminating heat. Additionally, the study surprisingly determined that the heat had no affect on the effort the birds put into foraging.
Previous studies have demonstrated the fatal nature of heat waves in bats, birds and even humans. This current study was the first ever to observe the effects of temperature increase on foraging and body condition in a wild bird population. To gather data for this study the researchers made observations and gained weight data on Southern Pied Babblers in five social groups. They obtained measurements for each individual every 2 hours for a total of 6 data collections a day. Birds are extremely susceptible to increased heat because they lose a large amount of water through evaporation even while resting and in the shade. They also use a lot of energy getting rid of heat through panting and gular fluttering (rapidly flapping membranes in the throat). The birds rely on foraging to resupply their energy and water store. However, this is a lose-lose situation because the activity required for foraging will make the bird even hotter and result in more energy loss and water loss. (Think of being starving and dehydrated and having to sprint in excruciating heat to get food and water.)
One of the main discoveries of this study, that the increased temperature had no effect on foraging effort, contrasted with previous findings on birds in arid environments. In a comparable study done on Dune Larks in the Namib Sand Sea, J.B. Williams found that “On hot days during the breeding season, Dune Larks seek shade to avoid the midday sun (J. B. Williams, unpublished data). Such behaviour constricts the foraging niche of larks, and probably constrains their energy and water intake in an environment where supplies may already be low” (Williams 2001). This result is fairly intuitive based on the assumption that birds avoid being active when they’re overheated (more formally termed thermal constraints). No concrete explanation for the alternate finding observed in this paper has been offered yet. Future research into the trend may be able to provide a reason.
Through correspondence with Amanda Ridley, contributor to this research paper and founder of the Pied Babbler Research Project, I gained a more thorough understanding of the goals and implications of the study. She explained that this paper is part of a collaborative research effort to determine what effects rising temperatures resulting from global warming will have on birds that already live in hot environments. This particular paper explained the short-term effects of increased temperatures on the Southern Pied Babbler. Most concerning was the finding that the birds studied gained less mass throughout the day as the temperature increased. Dr. Ridley explained, “long term, this could have serious consequences, such as individuals having insufficient resources to be able to invest in reproduction. Alternatively, individuals in poor condition may attempt to reproduce, with negative consequences for both the adults and the young that they produce (as a result of poor conditions due to heat stress).”
Dr. Ridley and colleagues are currently undertaking research efforts to further explain the impact climate change has on reproductive success and population growth. The findings could potentially direct conservation efforts to species that are predicted to suffer massive population loss as a result of global warming.
Du Plessis, K.L. 2012. The costs of keeping cool in a warming world: implications of high temperatures for foraging, thermoregulation and body condition of an arid-zone bird. Global Change Biology. 18 (10): 3063-3070
Williams, J.B. 2001. Energy expenditure and water flux of free-living Dune Larks in the Namib: a test of the reallocation hypothesis on a desert bird. Functional Ecology. 15: (2) 175-185
Photo courtesy of Ruan du Plessis. http://www.babbler-research.com/researchers.html