Animals usually display distinct activity patterns or rhythms that allow them to be classified as either diurnal (active during the day), nocturnal (active during the night) or crepuscular (active at dawn and dusk). These activity patterns have generally been considered inflexible – deviating from the normal pattern of behaviour was thought to put the animal at some sort of disadvantage. However, scientists are now discovering that, for some species at least, certain environmental factors can cause an animal to switch from nocturnal to diurnal activity and vice versa.
Adding to that body of evidence is a team of Australian scientists who have recently discovered that rainfall causes yellowfin bream (Acanthopagrus australis) to switch from primarily diurnal to nocturnal activity. The scientists found that these estuarine fish remain nocturnal for up to a week following rainfall before switching back to their normal diurnal activity.
Dr Nicholas Payne, a postdoctoral research fellow at the University of NSW, in collaboration with scientists from the NSW Department of Primary Industries and the University of Tasmania, made the discovery while monitoring the behaviour of yellowfin bream in the Georges River estuary in the south of Sydney. It is the first reported example of rainfall causing a reversal in an animal’s activity rhythm. “It is a stark reminder that...
