Ibises have a sixth sense, study shows

New research reveals they can detect vibrations in the soil made by their prey, such as earthworms

Hadedas, dubbed “African alarm clocks”, possess a sixth sense that is key to their range expansion in Southern Africa, new research on their extraordinary sensory capabilities has revealed.

The study by researchers from the University of Cape Town found that Hadeda ibises have a unique sensory adaptation that allows them to detect vibrations emitted by buried invertebrate prey, such as earthworms.

Published in the Journal of Avian Biology, it highlights the role of irrigation and the ibises’ remote-tactile foraging abilities in driving their habitat expansion in the region.

The authors noted that this ability is contingent upon the moisture content of the soil. When soil is watered in suburban and agricultural areas, it creates wetter substrates, and the ibises “capitalise on this environmental change to efficiently locate their prey, thereby facilitating their range expansion”.

“The findings of our study underscore the crucial interplay between environmental factors and sensory ecology in shaping the distribution and behaviour of wetland birds,” said Carla du Toit, a researcher from the university’s biological sciences department and the Fitzpatrick Institute of African Ornithology.

Du Toit, whose doctoral thesis formed part of the study, said Hadedas serve as a compelling example of how species adapt to humancaused modifications of their habitats. Remote-touch, the ibises’ sixth sense, enables them to detect vibrations from prey items in the substrate, similar to “a fusion of touch, hearing and echolocation”.

The research, conducted at the World of Birds sanctuary in Hout Bay in Cape Town, shows that the ibises are more successful in foraging in wetter soils, where vibrations spread more effectively.

“Our results … indicate that Hadeda ibises are able to use remotetouch in the absence of all other sensory cues (visual, auditory and chemical) to locate soft-bodied moving invertebrate prey buried under the ground,” the study noted.

Du Toit said the rapid adaptation of hadedas to changes in soil moisture levels underscores their resilience and adaptability.

She added that the study has improved the understanding of the sensory requirements of wetland birds, which is important for effective conservation strategies, especially when habitats are changing.

Soil irrigation “has not only facilitated the birds’ foraging activities but has also led to their proliferation in suburban and agricultural landscapes”, the authors said.

Their characteristic loud calls have become a familiar feature in urban areas, marking a shift from their historical distribution in the eastern regions of South Africa.

“Human activities have inadvertently paved the way for the expansion of Hadeda ibises into new territories,” Du Toit said

“As we continue to modify landscapes, it’s crucial to consider the ecological implications and potential cascading effects on wildlife,” she added.

Further studies will look at the tactile sensory systems of modern birds on a global scale, to understand the function and evolution of these senses and the associated organs.