From May to October, the powerful Southeast Trade winds dominate the Seychelles—carrying strong waves and shifting sand along our shores. Both Mauritius and Seychelles have similar cooler conditions and relief rainfall, called ‘tilapli iver’ in Mauritian Creole. ​

​I had experienced rough seas and heavy swell (‘lahoule’) in Mauritius, where I was not able to leave my workplace on Ile aux Aigrettes. However, this was nothing compared to the swell of Seychelles. What I described as a storm in Mauritius, where we cannot go out to sea, is a normal day during the Southeast monsoon or ‘vann swet’.
 
I did not know that the Southeast Trade winds were such a powerful wave with a persistent coastal current. This unconscious mindset led to a broken toe in my left foot. The doctor was shocked when they saw a fully fractured toe from falling down in the sea during the ‘vann swet’ while pushing the boat to leave Aride Island. I was happy that it was not worse.
 
I have been amazed to witness the beach of Aride shrinking day after day. The long, beautiful beach moved and left behind rocks and gravel. This erosion that Aride faces is natural. The sand is sometimes transported slowly, or on other days, you would wake up and a huge shift had occurred, transporting sand along the beach to another side of the island or offshore.
 
Since July, the coastline of Aride has been dancing. This kinetic landscape isn’t static. Sand doesn’t just drift—it disappears, and reappears elsewhere in unpredictable ways. Today, however, we have experienced a return of sand on the beach.  This was such a relief for me. It is still unclear, but maybe this is a sign that the North West monsoon might come earlier this year.
 
Another thing that I was not prepared for when I came to Seychelles was the Sooty tern colonies. Once there was a shift from the North West winds to the Southeast Trade winds, the birds started to arrive. At Ile Aux Aigrettes in Mauritius, we used bird decoys and recordings of bird sounds to attract Sooty terns. This was not so on Aride Island, where we needed to count a population of more than 6,000 breeding pairs of Sooty terns. This experience on Aride Island has marked me for life.
In Mauritius, Sooty terns have been locally extinct in a few of our islets because of the culture of eating their eggs and the presence of rats within the colonies. It is such a blessing to encounter the young generation that is willing to protect the Sooty terns in Seychelles, and the presence of laws to protect this species from exploitation. So, the Southeast Trade winds or ‘vann swet’ is not such a bad thing after all. We welcomed the birds and said goodbye to the only beach on Aride Island. So, cheers to ‘vann swet’!

What happens when two different species, live together, mate and reproduce? A new ‘hybrid’ species is sometimes born. Hybridisation between species plays an important role in evolution, though there is considerable debate about its significance. Around 25% of plants and 10% of animals are known to form hybrids with at least one other species. There is even evidence of hybridisation in modern humans, with up to 4% of DNA from all people living today attributable to Neanderthals.

In an astonishing discovery, on the remote St. Francois Atoll in Seychelles' Alphonse Group, conservationists have confirmed a rare hybridisation event between two different tern species: a Roseate Tern (Sterna dougallii or ‘Dyanman Roz’ in Creole) and a Black-naped Tern (Sterna sumatrana or ‘Dyanman Likou Nwanr’ in Creole). This is the second recorded time hybridisation between the two said species has been recorded anywhere in the world, the first being in Australia in 2004.

The colony of Black-naped Tern on St Francois - one of the three islands of the Alphonse group - has been monitored by conservationists from the Island Conservation Society (ICS) since 2008. According to a scientific publication published recently, using photographic evidence and field observations, ICS observed a single Roseate Tern that established itself within the colony of Black-naped Terns. It was then observed successfully mating with a Black-naped Tern to produce a ‘hybrid’ offspring with distinctive features of both parent species. For example, it had distinct red legs, a characteristic unique to Roseate Tern and not Black-naped Tern. The egg from this pairing also exhibited mixed features, for example, they were noticeably larger than that of both species, but also had pigmentation resembling the eggs of the Roseate Tern. Over time, Conservationists also observed a ‘hybrid’ mating with another ‘pure’ Black-naped Tern; a process called ‘backcrossing’.

Although hybridisation is known to occur in avian species, the study does not speculate why the two species have chosen to mate together. One suggestion is that Terns, as observed in Fairy Terns, are very loyal to their mate and have a tendency to return to a previously visited location or site fidelity. Hence, since this first pair of a Roseate Tern and a Black-naped Tern has been successful at mating and producing offspring at St Francois; they returned annually to repeat the same process.  

The findings have crucial implications for the overall population of both species. Seychelles hosts the only known breeding grounds for Black-naped Terns in the African region. In addition to St. Francois Atoll, both species of tern also breed on nearby St. Joseph Atoll, Étoile (an uninhabited low-lying coral cay of the Amirantes group) and Farquhar Atoll. Black-naped Terns also breed on African Banks, Bancs Providence, Aldabra and Cosmoledo Atoll in the Outer Islands. In contrast, Roseate Terns once bred at several of the inner islands, but survive today only at Aride Island.

Black-naped Tern is a relatively scarce species in the Seychelles with an estimated 245 to 345 pairs – the entire breeding population of the Afrotropical region.  As for Roseate Tern, although it has a wide distribution around the world, its population is declining. It is estimated that 1,600 pairs of Roseate Tern visit the Seychelles from May to August to breed only. The majority (over 1,200 pairs) breed on Aride Island and rely on the protection of this island as a Special Reserve for their continued survival.

With both species being relatively in low numbers throughout Seychelles, this study highlights the need for further study to assess the extent of genetic mixing and its consequences on the evolution of both species on St Francois. Since this occurrence is only in one location, there is a risk that the population of the ‘pure’ Black-naped Tern will continue to inbreed within itself and with the Roseate Tern. However, the conservation implications of hybridisation are disputed. While the process might threaten rare species, it could also save a rare lineage from extinction by introducing genetic diversity. A "pure" lineage could harm conservation by lowering genetic diversity and adaptive potential, particularly in species with low populations.

It is uncertain what will happen to the unique and distinct characteristic of both species if this continues. This is a fascinating and rare aspect of avian biology that is unique to Seychelles and the Alphonse Group and that merits more research. This hybridisation phenomenon also underscores the fragility and biodiversity of Seychelles' ecosystem, particularly in the protected St. Francois Atoll—a critical site for seabird conservation.   

​My name is Russell Brown and I am a zoology student from England, studying in Cornwall. As part of my master’s, I had the opportunity to come out to Aride Island specifically to study the mice here. I aimed to gather information that would help estimate their population on the island, as well as study their home ranges. I was here during the gap between my third and fourth years of study to collect data for the research project.

Why This Research Is Important
Aride is home to many ground-nesting birds, including the White-tailed Tropicbird, Brown Noddies, and Shearwaters. It is currently unknown whether mice prey on their eggs or those of smaller species such as skinks. The first step in determining this is to estimate the number of mice on the island and understand how far an individual travels from its home. The information gained from this study could help guide future conservation efforts, including the potential eradication of mice from Aride, as this species was accidentally introduced by humans.

Of Boat Rides and Helicopters
While on Aride, I also assisted with the Sooty Tern census, cared for Aldabra Giant Tortoises, and excavated hatched Green Turtle nests—something I’m quite experienced in due to previous work on a turtle project. I was also heavily involved in launching the boat and other day-to-day tasks. At this time of year, leaving the island and taking trips to Praslin is an adventure. You can get knocked around by the waves and have to hold on tight. Being ‘airborne’ in the boat is my idea of heaven and was a highlight of my time on Aride. Another incredible experience was when a helicopter was used to airlift materials between a visiting barge and the island. Pulling straps off equipment while a helicopter hovers 20 metres above you is a truly unique feeling!
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Life on the Island
In my spare time, one of my favourite things to do was explore and photograph the wildlife and scenery. Capturing the perfect shot of a bird in flight is incredibly rewarding! I never expected to stay for over two months on a nature reserve island—especially not during the Southeast monsoon—so when the opportunity came up, I had to take it. It has been an absolute honour to work alongside the incredible people who dedicate themselves to making the island a sanctuary for all kinds of wildlife, whether birds, reptiles, invertebrates, or plants. All of this comes together to make Aride Island an incredible and truly unique place!