How do animals call to each other over distances?
UNSW Sydney researchers studying the evolution of calls from over 103 mammal species think they may have found a pattern.
The findings of their study, just published in Journal of Mammalian Evolution, collected data from 81 research papers and found a pattern: a difference between land and ocean animals.
“Environmental factors generally played the biggest evolutionary role in deciding how far land mammals can communicate but biology – specifically, size – was the biggest influence for underwater mammals,” says Dr Ben Walker, lead author of the study and evolutionary ecologist at UNSW.
“In other words, land mammal calls have evolved mainly in response to environmental pressures while aquatic mammal calls evolved in response to changes in body size.”
The study found a simple pattern: the bigger the marine mammal, the further their calls reached: blue whales weigh about 150 tonnes and are up to 30 metres long, have songs that can travel up to 1600km. On the other end of the size scales are otters, which weigh about 28kg and whose calls only travel 1km.
On land, the story is ‘different’, the study says: the size of the animals’ ‘home range’ (turf) is the leading factor in how far their calls travel but this distance is heavily influenced by habitat, the purpose of their call and whether they are social.
The study says territorial calls (calls warning others to back off from their domain) travel further than other types of calls, while social species, like elephants, can ‘talk’ further than solitary species.
ANIMALS AND THEIR HABITATS
“The type of habitat (that) land mammals lived in also played an important role but not in the way we expected,” Dr Walker says.
“Mammals that call in closed environments, like rainforests, evolved to have relatively further calls than mammals in open environments, like savannahs. This really surprised me, as I was expecting the opposite.”
The UNSW says the findings challenge long-held scientific assumptions that only environmental factors affect the evolution of animal sounds – and highlight how their communication might be affected by future evolutionary pressures.
“We build on recent research showing that the environment’s role on land is more nuanced than previously thought,” says Dr Walker.
“We also show for the first time that mammals in aquatic environments are following their own rule set entirely.”
UNIQUE CHALLENGES
Human changes to habitats are already affecting animal behaviour across the planet like bats reducing their use of echolocation during music festivals and ship noises causing stress in whales, says Dr Walker.
“Our finding that land mammals in closed habitats have evolved to have relatively further sound distances than those in open habitats is important because if land clearing happens in a closed habitat, a mammal call might travel further than the animal’s intention with deadly consequences.
“For example, an unsuspecting possum could make a call that accidentally reveals itself to potential predators. Without its usual abundance of nearby trees, the possum might not be able to escape vertically, as closed-in habitat species tend to do.
“Without meaning to, the possum has inadvertently risked becoming someone’s dinner.”
Underwater, past research showed that mammal growth was stunted due to whaling and environmental impacts.
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