It is white, and the head is slightly ocher. Black feathers extend its wings and tail. Wingspan exceeds 1.60 meters. Cape Bean (Morus capensis), a bird symbolic of the coasts of South Africa, which is included in the Red List of the International Union for Conservation of Nature (IUCN). The last census, in 2018, was only 250 thousand individuals and the population was in sharp decline. The reason: poaching decimating his stocks of anchovies and sardines, but also the presence of a formidable predator, the fur seal (Tropical Arctocephalus) which disturbs his lifestyle.
In a study published in early March in Communication biologyan international team of researchers describes how birds, out of fear, move away from the coast at night and how some make do with fish waste for food during the day.
The adaptation of the behavior of a group of potential prey to the arrival of a predator and the reorganization of the ecosystem is a phenomenon known to scientists. They formalized it as“ environment of fear » or “ scene of fear ». The concept was popularized after the wolf was returned to the American Natural Park in Yellowstone in 1995.
In a study published in 2001, researchers showed that merely a change in elk behavior due to fear of the wolf had more consequences for its population than predation itself. Then the population was reduced by half. Another consequence is that large areas are abandoned by potential prey to wolves, making way for new animals and plants. These indirect cascading effects have changed the entire ecosystem… “ for riverbeds ! » Write the authors.
Movements based on fear
This phenomenon is also found in the marine environment. In the study published in Communication biology, French and South African researchers tracked Cape boobies in the Benguela region off South Africa. Located at the confluence of the deep cold-water rises and Agulhas Current off the Cape of Good Hope, the waters here are particularly rich in nutrients and abundant marine life.
After equipping the birds and sea lions with lighthouses GPSscientists note that when night falls, the insane adopt two strategies: 28 They returned to the nest in their colonies on Earth, when 72 The percentage remaining on the surface of the water. But while the Cape tits can fly up to 50 kilometers from the coast during the day, the birds remaining in the sea at night flee for up to 13 kilometers, when sea lions watch over them to better bite them. This behavior is effective, as the risk of predation is reduced by 25 . %.
- Monitor Cape booby in Lambert Bay, South Africa. Wikimedia Commons /Copy by–Ha 3.0 / Avitopia
The birds also tend to hunt during the day in areas less frequented by sea lions, and are often less gifted with small pelagic fish. They even came up with an innovative strategy, he says Reporter Nicholas Corbin, one of the study’s authors: Feeding on fish droppings collected in the wake of fishing vessels. This less dangerous behavior towards a predator is less favorable to the health of the birds. “ These remains constitute Fast food for birdshe’s kidding, Less energy and less good for health. »
Feeding these birds is even more complicated because they also face dwindling fish resources due to overfishing and global warming. “ Throughout the colony, there is a decrease in the status and survival of adult boobies. and reproductive success in general. This is particularly related to reduced food resources »Nicolas Corbyn concludes. So much so that today’s idiot is threatened.
areas to protect their resources
“ Other large marine predators, such as the white shark and orca, add layers of complexity to the seascape of fear »Write the authors. Thus, sardines and anchovies are afraid of boobies, who, in turn, flee from sea lions, who dodge themselves in front of great white sharks who finally squeeze in front of the killer whale. Thus, each link in the food chain adapts its daily movements to the threat of predation, thus making up the entire ecosystem.
According to Mr. Corbin, in order to protect cape eels, it is necessary to conserve their food resources and to form vast areas not to harvest small pelagic fish off the coast of South Africa. Because, right now, he’s alone “ Small coastal marine protected areas » It is defined around. The researcher explains that these small spaces have the disadvantage of concentrating predators in small areas, which increases the intimidation of birds.
Can we imagine marine protected areas resilient to adapt to the nocturnal movements of the Magdavo Cape? ? If the idea is technically tempting, David Grémillet, another co-author of the study, doubts the effectiveness of such a procedure: “ We must first create true marine protected areas, which constitute true exclusion zones. » Currently, MPAs are still suffering from very lax policies, harming the biodiversity they are nevertheless meant to protect.