10 Giant Tortoises Reshape the Aride Ecosystem

The reintroduction of ten Aldabra giant tortoises (Aldabrachelys gigantea) – a species recognized for playing the role of a large terrestrial herbivore – on the northernmost granitic island in the Seychelles, restored ecological functions absent for over 180 years in just six months. 

Translocated from nearby Frégate Island, the tortoises restored critical processes like seed dispersal and vegetation management.

Giant tortoises became extinct on Aride Island nearly two centuries ago, and with them, important processes that maintained the island’s habitat were lost. Their reintroduction confirms that they act as ecosystem engineers by performing three fundamental ecological functions: controlling the cover of exotic plants; accelerating decomposition and nutrient recycling in soils through the consumption of leaf litter; and dispersing native plant seeds through their droppings after ingesting fruits. 

Conducted by researchers from the Doñana Biological Station (EBD), the National Museum of Natural Sciences (MNCN), the Royal Botanical Garden (RJB) – all part of the Spanish National Research Council (CSIC) – and the University of Exeter, the study demonstrates that reintroducing a small number of giant tortoises is a cost-effective restoration strategy capable of reestablishing lost ecological interactions. 

The study "Individual variability shapes interaction rewiring and fosters ecosystem restoration by reintroduced giant tortoises in the Seychelles", which highlights how these 10 Aldabras dramatically reshaped the island's ecosystem, was published in the journal Restoration Ecology and released on April 16, 2026.

The dispersal of more than 11,000 seeds in two months helps to gauge the extent of the process recorded by scientists during the initial monitoring of the animals. As nearly nine out of ten seeds belonged to native species, the movement of the reptiles may favor the regeneration of original vegetation in areas where introduced plants have gained space. 

The consumption of 54 exotic species was also recorded as relevant data because invasive plants can compete with local flora for light, water, and nutrients. By feeding on these species, the tortoises reduce some of the pressure on native vegetation and alter the growth dynamics in the territory, according to the researchers’ assessment.

The research also pointed out behavioral differences among the reintroduced individuals, a fact considered relevant to assess how each animal contributed to the ecological restoration of Aride Island. 

In fact, only three of the ten tortoises accounted for more than 80% of the native seed dispersal in two months, while others had a greater role in the consumption of exotic plants or in nutrient recycling. For this reason, the team advocates that conservation projects evaluate which animals play broader ecological roles, as individuals of the same species can generate different effects in the ecosystem’s recomposition. 

The case of the tortoise identified as T08 was used by the scientists to exemplify this variation in behavior observed during monitoring conducted after reintroduction on the island. According to the study, this individual demonstrated greater efficiency in consuming exotic flora, strong native seed dispersal, and balanced ingestion of native and introduced plant matter compared to other monitored tortoises. 

The finding led the researchers to highlight behavioral diversity within the same species as an element to be considered in ecological restoration actions. 

The study does not claim that any release of animals will produce the same result, nor does it indicate that reintroduction can be done without planning in other island ecosystems. For this type of action, experts consider it necessary to evaluate species, environment, ecological history, health risks, and subsequent monitoring, especially on islands, where imbalances can spread quickly.

Researchers advocate that future restoration initiatives consider the so-called effective number of individuals capable of sustaining ecological functions, and not just the total number of animals reintroduced. This concept broadens the traditional analysis, which usually prioritizes the genetic viability of a reintroduced population, by also including the individuals’ ability to recover natural processes in the environment. 

The six-month interval does not represent complete restoration of the island, but indicates, according to the study, that functions previously absent were measurably resumed after the reintroduction of the tortoises. 

Cold-blooded Murder

Tortoises, especially the terrestrial varieties are generally known to be herbivorous. 

But scientists in the Seychelles captured footage of one of the hulking reptiles engaged in an act of cold-blooded murder.

The video shot on July 30, 2020 showed an adult female Seychelles giant tortoise (Scientific name: Aldabrachelys gigantea hololissa) slowly approaching a lesser noddy tern chick with its mouth open, which is a typical aggressive gesture. 

It appeared that the chick had fallen from its arboreal nest in the treetops and was stranded on a log. Although it backed away to the edge of the log and defended itself from the tortoise with pecks, it was all a futile effort. The larger tortoise clamped its jaws down on the bird’s head, effectively killing it. 

The tortoise then climbed off the log to retrieve the dead carcass and swallowed it whole, making it a protein-rich addition to its plant-based diet. The whole morbid interaction took place in seven minutes. 

This incident was recorded in a study authored by Anna Zora of the Fregate Island Foundation in the Seychelles and Justin Gerlach of Cambridge University and published in Current Biology.

 

According to the study, the footage is the “first documented observation of a tortoise deliberately attacking and consuming another animal” and represents “an entirely novel behavioral strategy for any tortoise species”. 

The team wrote: “There are reports of Galapagos giant tortoises squashing birds under their carapace and we have heard of tortoises on Aldabra squashing crabs, but these are anecdotal and although it is implied that the act is deliberate, this is unclear”. 

What caused the tortoises to change its diet? The extensive environmental restoration on the island which led to a boom in both tortoise and tern populations might have led to this eventuality. 

When tern chicks fall from their tree nests, they are prey for a variety of predators such as lizards and crabs. The island’s tortoises might have simply adopted its diet to get easy meals.

“At present we do not know how extensive the behavior is on Frégate; future studies will determine whether it develops further or expands more widely in the tortoise population”, Zora and Gerlach concluded.

200,000 Coronavirus Cases in Africa

The total number of coronavirus cases in Africa passed 200,000 yesterday, according to the World Health Organization’s office for the region. The continent had added 100,000 cases in eighteen days. 

According to the latest update by the UN health agency, 201,157 people have tested positive for the virus across the 54 countries in Africa, of whom 90,374 have recovered and 5,486 have died, the UN health agency said. 

The Top 7 African countries for confirmed cases are still the same as the list I had put out in my May 23 post (“The Covid-19 Situation in Africa”) – just that there has been a reshuffle in their positions, Nos. 3 to 7:

BTW, these seven countries constitute 72.3% of Africa’s total (or 1.9% of cases worldwide). 

Even for fatalities – where the Top 7 countries make up 81.8% of Africa’s total (or 1.1% of deaths worldwide) – it's the same seven countries as I last reported in May – except for a change in positions, Nos. 2 to 7. 

And just to compare with the Bottom 7 (i.e. the Least Affected countries):

The Covid-19 Situation in Africa

More than three months have lapsed since Egypt became the first country in Africa to confirm a coronavirus case. Since then, the outbreak has reached every nation on the continent of 1.2 billion people – with 100,666 confirmed cases and 3,105 deaths on Friday, according to Africa CDC. 

No doubt Africa recorded just a wee fraction of the world's coronavirus cases – a mere 1.9%. 

Also WHO modelling has predicted that Covid-19 would move more slowly through Africa than elsewhere. It's very comforting to know, that’s for sure.

Still, the fact remains that the virus is raging in pockets of the continent. 

And it has been hit hard by the economic fallout from global trade disruptions, falling oil and commodities prices and the lockdowns deployed to fight the disease's spread. That can be just as hurting. 

I read that the presidents of Ivory Coast, Kenya, Niger, Senegal and Sierra Leone on Tuesday are already complaining that wealthy countries are failing Africa, with pledges of financial support and debt relief falling well short of the continent's needs as it battles the coronavirus pandemic. 

But it’s not only Africa that is affected – but everywhere too.

Already, the global economy is shrinking by around 5%. According to World Bank estimates, up to 60 million people could be pushed below the poverty line in their latest apocalyptic prediction. 

World Bank president David Malpass (right) said they have so far loaned money for emergency programs in 100 countries, accounting for about 70% of the world’s population, in response to the coronavirus crisis. 

He said the money would “reinforce healthcare systems” as well as pay for medical equipment and supplies.

Many countries' economies are already in dire straits.