After 9,000 years of thriving in the absence of mammalian predators, tammar wallabies still startle at some signs of dangerous mammals, according to an Australian study.
No mammal has threatened the wallabies Macropus eugenii on the unsettled part of Kangaroo Island since the island separated from the Australian mainland. The scientists presented caged wallabies with sights and sounds that might signal unfamiliar but dangerous predators.
The sight of a taxidermist-prepared fox stopped the wallabies from foraging and sent them into a frenzy of thumping their hind feet and peering around. The sight of a similarly stuffed cat likewise interrupted dinner and provoked vigilance, report Daniel T. Blumstein and Christopher S. Evans of Macquarie University in Sydney and their coauthors in the September Behavioral Ecology.
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In contrast to the sight of a potential predator, recordings of dingoes howling didn’t evoke much reaction, especially when compared with the calls of a familiar danger, the wedge-tailed eagle.
The wallaby experiments suggest that wariness about things that look like mammalian predators has endured, while concern about their sounds has faded, Blumstein and his colleagues propose. They say that the wallaby reactions demonstrate an evolutionary quirk called relaxed selection. When changing circumstances reduce the pressure for an animal to maintain some adaptations, such as wariness around predators, those adaptations linger for generations and then fade away in parts (SN: 10/9/99, p. 237).