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A global meta-analysis carried out by a hundred scientists from around the world demonstrates the impact of climate change on the reproductive success of birds and reveals that not all species are affected in the same way.
More than 40 years ago, scientists began to warn of the dangerous trends of climate change and its possible consequences for the world and the human species itself. Unfortunately, its data, interpretations and predictive models have been systematically ignored. As a result, over the course of these four decades, a "change" turned into a "crisis" has reached the present in the form of a climate "emergency" due to the chain reactions that ecosystems are beginning to experience in relation to the increase in the average surface temperature of the planet.
When we talk about a climate emergency, we are not referring exclusively to the accelerated increase in the global temperature of the planet caused by the impact of human activities, but to the negative consequences that this entails on a multitude of "vital signs" of the planet, such us biodiversity.
Several studies have already shown that the increase in global temperature causes phenological changes, altering the moment in which birds reproduce, which can compromise the stability of their populations. Migratory birds reach their breeding grounds earlier, and the eggs of many clutches hatch early in the season in response to high temperatures. However, few studies have examined how climate change is affecting their reproductive success, that is, the number of offspring produced by birds.
Over the past 50 years, the Earth's average surface temperature has increased by 1ºC, which is enough to compromise biodiversity conservation in many parts of the planet. The bearded vulture is an example of a large and non-migratory bird for which a decrease in offspring production has been detected in relation to climate change (Photo: Pilar Oliva-Vidal).
A new study led by Dr. Lucyna Halupka from the University of Wroclaw (Poland), and signed by more than 100 scientists from research centers and universities around the world, including Dr. Antoni Margalida, from Research Group in Game Resources and Wildlife Management of the Instituto de Investigación en Recursos Cinegéticos (IREC – CSIC, UCLM, JCCM) and the Instituto Pirenaico de Ecología (IPE - CSIC), confirms that the increase in the global temperature of the planet has affected negatively to offspring production in large and migratory birds, while small and sedentary species appear to benefit.
To reach this conclusion, the researchers examined breeding data from 201 populations of 104 bird species (which correspond to the monitoring of 745.962 clutches) from around the world between 1970 and 2019. The study controlled for phylogeny, life history traits of species, migratory habits, latitude, direct human impacts, and local changes in temperature or precipitation.
The results show that more than 56% of bird populations showed a downward trend in offspring production, especially large and migratory birds, while 44%, represented mostly by small and sedentary birds, showed a positive trend. Thus, everything seems to indicate that non-migratory and small-bodied birds could better adapt to ecological disturbances resulting from climate change, while the survival of large migratory bird populations could be seriously compromised as temperatures rise.
The reason for this differentiation is unknown for now, but scientists believe it could be because large birds tend to produce fewer offspring overall, take longer to mature, and have more time between generations. It is about various factors that can slow down a bird species' ability to adapt to climate change.
On the other hand, smaller birds tend to disperse heat more easily, which could help them regulate their body temperature more efficiently in the face of an increase in environmental temperature. Finally, climate change may also be reducing food and water availability in some areas, and smaller birds may be better equipped to compete for limited resources.
Some of the species with the largest decreases in offspring production include the Montagu’s harrier and the white stork (large and migratory), the bearded vulture (large, non-migratory) and common house martins (small, migratory). On contrary, bird species with increased offspring production include the Eurasian sparrowhawk, the Eurasian wrynecks, collared flycatchers and prothonotary warblers.
Overall, the authors attribute the changes in offspring production to the combined effects of global warming on the ecological and life history traits of bird species. According to the authors, the rapid decline in population size of some bird species documented in other studies around the world could be partially due to these changes in decreased productivity (fewer offspring produced).
The scientific publication of this research is available at:
- Halupka, L., et al. 2023. The effect of climate change on avian offspring production: A global meta-analysis. Proceedings of the National Academy of Sciences 120 (19), e2208389120.
