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Mountain wagtail

Researchers find climate change is decreasing the size of animals

Researchers from the University of Cape Town (UCT) confirmed that climatic variation is declining animal’s body size by gathering evidence for 23 years between 1976 and 1999.

Associate Professor Res Altwegg and Dr Birgit Erni, along with co-workers examined Mountain wagtail’s (a type of bird) weight change along the Palmiet River in Westville, KwaZulu-Natal. The study has been published in the journal Oecologia.

For the past 100 years, global temperature has increased by 1-degree celsius causing extreme effects on the earth and its ecology. The fossil record shows that aquatic as well as terrestrial animals have become small-sized during the past periods of global warming.


According to scientists, existing global warming could result in smaller animals, although we don’t have sufficient evidence. Researchers on observing a group of wagtails living along the Palmiet River concluded that the idea that climate change can shrink Earth’s animals is true.

Professor Altwegg said that larger animals can tolerate cold conditions better than smaller animals, so one could expect that a warming climate is relatively more advantageous for smaller animals. He also said that although the conclusions supported the idea that climate change is the reason behind declining bird’s body size, there are various other factors that are responsible for this.

Mountain wagtails are slender black, grey and white birds living near small fast-flowing rivers across sub-Saharan Africa. They got their names because of the up-and-down pumping movement they do with their tails. Researchers knew that the temperature near the Palmiet river had increased by 0.18 degree Celsius based on data from the local weather station.

The conclusion drawn showed that along the Palmiet river under high temperature, mountain wagtails had become lighter and lighter, wagtails have started replacing heavier ones in the population and have survived better. This shows that evolutionary pressure is responsible for this.

Professor Altwegg said that other studies didn’t have detailed information to prove that temperature is the actual reason behind the declining of animals by changing their capability to live in various places of the world. Altogether, their outcomes support the concept that climate change is responsible for animals’ declining body size, their interaction and seasonal behaviour but scientists do not have clear evidence in support of other consequences, on the size of animals whether they will respond more extremely, not at all or may respond negatively increasing the body size.

This effect could cause changes across ecosystems. Body size is an important indicator of an animal’s fertility, lifespan and ability to survive stress (food scarcity). It also affects the amount of food they need, their vulnerability and the type of food they eat.

Journal Reference: Oecologia

About the author: Kshitij Kumar Moderator
Kshitij has always been passionate about Science and Technology. He is a Mechanical Engineering graduate from IIT Jodhpur. Kshitij has worked in many fields of Science and Marketing. Along with managing backend and technicalities of the website, he is also one of our editors and marketing managers. Kshitij was the one who came up with the idea of connecting people interested in Science and built a team which is now ScienceHook.

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