By Rory Galloway Science writer
- 2 December 2017
Two male Rodrigues solitaires fight
over a female in the background using club-like wings by Julian Hume
The extinct Dodo had a little-known relative on another island.
This fascinating bird ultimately suffered the same fate as its iconic cousin,
but we can reconstruct some of its biology thanks to the writings of a French
explorer who studied it during his travels of the Indian Ocean.
In the middle of the 18th Century, at around the time the US was
signing the declaration of independence, a large flightless bird quietly became
extinct on an island in the Indian Ocean.
Today this bird is all but forgotten.
Early explorers to Rodrigues described a "Dodo" living
on the tiny forested island. Males were grey-brown, and females sandy, both having
strong legs and long, proud necks. But despite outward similarities to the
iconic Mauritian bird, this wasn't in fact a Dodo, but the Rodrigues solitaire.
If you look up Rodrigues in satellite images, you can see a huge
ring of submerged land around the central island, over 50% of the original dry
land is thought to have been lost under the waves due to sea-level rise and the
island subsiding into the bedrock.
That was the stage for the evolution of the huge bird, over
millions of years.
The small island of Rodrigues is part of Mauritius in
the Indian Ocean
It's likely this
shrinking habitat caused an increase in competition for food and territory
between individuals of the species, and perhaps as a result of this, the
solitaire evolved a club-like bone growth on the end of each wing.
It used this against
other solitaires in territorial boxing matches. These would have been quite a
sight, as the males stood almost a metre tall and weighed nearly 30kg, while
the females were sandy-coloured and were half that size.
Considering its
obscurity today, we have amazingly detailed descriptions of the solitaire's
behaviour.
This is because of the
diary of a man named François Leguat.
He was part of a group
of seven Huguenot men, who had set out from France to establish a colony of
French protestant refugees on the island of Reunion.
Instead, they were
marooned for two years on the island of Rodrigues from 1691 to 1693. In that
time, they made the first attempts at establishing a settlement on the island.
Leguat encountered the
solitaire in this time and wrote about it in his diary:
"Of
all the birds in the island the most remarkable is that which goes by the name
of the solitary, because it is very seldom seen in company, tho' there are
abundance of them… Its eye is black and lively, and its head without comb or
cop. They never fly, their wings are too little to support the weight of their
bodies; they serve only to beat themselves, and flutter when they call one
another."
Francois Leguat was marooned on the island of Rodrigues
in 1601 where he encountered, described and drew the forgotten Rodrigues
solitaire. Alamy
Leguat described how
the birds used their short wings to make a loud rattling sound that could be
heard "two hundred paces off".
He also described the
bone on their wing which grew larger at the end, forming a mass under the
feathers "as big as a musket ball".
This was used as a
club-like weapon, and along with their beak, was "the chief defence of
this bird".
These are tantalising
clues showing us what the species was like in life, and are some of the first
detailed behavioural descriptions of any bird. It's likely that the rattling
sounds were used both to attract the attention of a mate and as a warning to
same-sex rivals, but it's highly unusual for birds to use their wings to make
sounds for long-distance communication, making even more acute the loss of such
a unique animal.
The solitaire would
have been quite striking in life, and in his writings it is clear Leguat had
some affection for them: "No one feather is
straggling from the other all over their bodies, they being very careful to
adjust themselves, and make them all even with their beaks. "
Today, we have
numerous bone remains of the species, and these come from caves and deposits
across the island.
They can be found
reconstructed in museums on the island and elsewhere, but there are no records
of a live specimen leaving the island, and there are no preserved skins of the
animal left.
Studying these bones,
scientists, including extinct bird expert Dr Julian Hume, have noticed an
abundance of healed bone fractures on the sternum and wings.
Comparing these with
Leguat's descriptions, he theorises that the birds would frequently hit each
other so hard with their wing-clubs that they were breaking the bones of their
rivals.
So these descriptions
from the marooned Huguenot are incredibly valuable, allowing us to interpret
the specimens we have left.
They even show the
breeding behaviour of the bird, which was likely monogamous:
"They never lay but one egg, which is much bigger than that of a
goose. The male and female both cover it in their turns, and the young is not
hatch'd till at seven weeks' end: All the while they are sitting upon it, or
are bringing up their young one, which is not able to provide itself in several
months."
The Victoria crowned pigeon is the biggest living
pigeon species, closely related to the solitaire, it has a growth on the
wing-wrist that it uses for defence. Getty Images
Monogamy and shared
parental care are common in other pigeons we see today, including close living
relatives of the solitaire: the nicobar pigeon and crowned pigeons.
Like these pigeons,
the solitaires likely fed their chicks "pigeon milk", a nutrient rich
soup produced in the walls of the throat pouch of the parent birds.
Two parents are able
to produce more food, and so a larger chick, increasing their competitive
advantage against other birds in the fight for territory.
Parts of the behaviour
of the solitaire described by Leguat, including the aggression, can be seen in
the crowned pigeons, which will hit anything that approaches them on the nest
with small bone spurs on their wing-wrists.
But in the solitaire,
with its evolutionary cauldron of the shrinking island of Rodrigues, these
adaptations were pushed to an extreme.
The story of the
solitaire may sound like deja vu. When Leguat and his fellow castaways
eventually escaped Rodrigues on a cobbled together raft, they drifted 200 miles
to Mauritius, the island home of the Dodo.
This was strangely
coincidental because 1693 was the very year that the Dodo is thought to have
gone extinct.
Sadly, it meant that
he couldn't put his descriptive writing to work on the solitaire's better known
relative. Yet despite this, today the comically described Dodo is far better
known than its elegant relative.
That's likely because
it was initially thought the solitaire was a Dodo living on
Rodrigues.
Early observers on
Rodrigues called the solitaire the "Rodrigues Dodo". But the two
birds were really subtly different evolutionary outcomes to similar selective
pressures and, as such, represent an incredible experiment in evolution.
The two birds were, however, close cousins.
Paradise island: Rodrigues today. olivierdesigns
Both birds descended
from a small species of pigeon that likely flew to the islands about 10 million
years ago.
On arrival, they found
an abundance of food and an absence of predators on both islands.
This was a fruit-eating
pigeon's paradise, so flying became unnecessary, and they lost the ability in
favour of larger size. This is where the biology of the bird challenges some
recent scientific dating of the rocks of the island.
Genetic evidence
suggests a gap of around 12 million years between the last gene exchange
between the Dodo and the solitaire, while some rocks dated on Rodrigues suggest
the island is 1.5 million years old.
Dr Julian Hume
suggests it is likely the species island-hopped down to the Mascarene islands before
becoming genetically isolated due to the loss of flight on the islands some 12
million years ago, showing how the age of the island is in dispute.
Despite arising in
very similar environments, the two birds evolved different adaptations for the
same problems.
The Dodo, on the
larger island of Mauritius, had a much larger beak with a hooked tip. Dr Hume
believes that they probably used that bill to hit each other in territorial
disputes.
So it's quite possible
that the Dodo was similar to the solitaire in being highly aggressive and
territorial, yet lacking the specific adaptation of the rattling clubbed-wings
for defence.
In fact, the Dodo's
wings were tiny and it's thought they were used just for balance.
We have no
descriptions from life of how the Dodo reproduced, but Leguat wrote that the
solitaire laid a single egg on a nest raised off the ground on pine leaves.
It's likely the Dodo
behaved in a very similar way, and bird palaeontologists now think this was the
Achilles heel of both species.
Mauritius had been
settled by the early Portuguese and then Dutch mariners as a stop-off on their
trading journeys. These groups brought rats, cats and domestic pigs with them
to the island, and these were left to run feral.
Unfortunately, the
large single egg of the Dodo was a perfect feast for the invading mammals, and
despite their formidable ability to fight each other for territory, they had
lost any instinct to protect their egg against these invaders.
Likewise the
solitaire. It was protected for a hundred years by the isolation of its remote
and tiny island, but, ultimately, a combination of development, rats, and cats
sent the other Dodo to the same fate.
This
article was inspired by research for the radio documentary 'Can
we revive extinct species like the Dodo?' CrowdScience was on the BBC World Service at 20.35 on Friday 1
December, or afterwards you can download the CrowdScience
Podcast to listen on demand.
