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Entries in Galapagos Islands (4)

Tuesday
Jul242007

The seabirds of the Galapagos Islands

Tuesday morning was devoted to the seabirds of the Galapagos Islands. Of the 140 bird species found on the islands, 89 are seabirds. Two terns (the Sooty and Brown noddy), two boobies (the Blue-footed and Red-footed), two frigate birds (Magnificent and Great), Storm Petrels, Red Billed Tropic Birds and the Waved Albatross all nest on the islands in significant numbers. The Galapagos has the world’s largest colony of Red Footed Boobies and 30% of the world’s Blue Footed Boobies. Other seabirds have settled permanently and are endemic to the Galapagos, including the Nazca Booby, the Lava Gull, the Swallow-tail Gull, the Galapagos Petrel and endemic subspecies of Audubon’s Shearwater and the Brown Pelican. The most specialised endemic is the Flightless Cormorant, which is the largest cormorant in the world at one metre tall and 4kg, and the only one which cannot fly. Its wings have become tiny (unlike the penguin it swims with its feet and not with its wings) and the carina (keel) has become vestigial. 

We had seen seabirds throughout the Galapagos Islands, but we went to North Seymour to visit their breeding site. The entire flat island was covered in nests, mostly Blue Footed Boobies, Magnificent Frigate Birds and Great Frigate Birds, but we also saw the Nazca Booby and Red Swallow-tail Gull nests. The Blue Footed Boobies take their name from their clumsiness on land and their awkward courtship dance - “bobo” means stupid in Spanish. The Blue Footed Booby males offer sticks to females during courtship in a very similar behaviour to that of mainland Boobies, even though Blue Footed Boobies on the Galapagos no longer make nests with twigs (the Red Footed Boobies do). We watched the juvenile Boobies practise their stick behaviour, they were not very good at it and looked puzzled as the sticks flew from their beaks. Other juveniles tried the “sky pointing” and “foot waving” courtship behaviour, in a very amusing display.

 

Unlike Blue Footed Boobies with a single egg, Nazca Boobies always lay two eggs. The one that hatches first pushes the other egg out of the nest. It isn’t clear why this occurs, either an evolutionary relic from times when Nazca Boobies had a rich enough habitat to raise two chicks, or an insurance policy in case one egg fails to hatch.

 

We watched the magnificent acrobatics of Frigate birds, able to swoop and harass other birds until they regurgitate on wing, plunging down to catch the half-digested meal before it hits the water. This aeronautic skill is essential for Frigate birds as they have a tiny uropygial gland and can’t waterproof their feathers, so unlike other sea birds entering the water would cause them to drown. The most prominent feature of the Frigate Birds on North Seymour, however, was not their flying but the bright red throat pouch on the males. To attract a mate they inflate their scarlet pouch with air, making it nearly the size of their entire body and forcing their necks to bend backwards.

Sadly North Seymour was the end of our Galapagos voyage, so we had to make our way back to Baltra. Our final vision of the Galapagos was of the ferry terminal, where all the benches were occupied with sleeping sea lions.

 

We flew from the Galapagos to Guayaquil. Guayaquil was founded in 1538, and is now the biggest city in Ecuador with 3 million people. The city was very festive, perhaps because we arrived on Bolivar’s birthday, or perhaps because the following day was the anniversary of the founding of Guayaquil. We walked to the central park, with its statue of liberal devoted to Simon Bolivar and the founders of Ecuador, and the Parque Bolivar where excited kids watched iguanas mating in the plaza. We saw the main Cathedral, originally built in 1547, but now a reconstruction after it burnt down. Our guide bought lottery tickets at the door and prayed inside for them to win (he was a terrible guide and acted like a tout). The waterfront of Guayaquil is beautiful, with lots of people running around and a perfect path to meander along. We saw the Presidential Procession as the President arrived in Guayaquil for the following day’s celebration, and we climbed the 480 steps up the Las Penas, the old town. We had dinner at an excellent seafood restaurant which did the most amazing mushrooms in garlic and wine sauce, but we had to leave early as Lydia felt ill.

Monday
Jul232007

Bartolome Island and Sullivan Bay 

Monday we visited Bartolome Island and Sullivan Bay on Santiago. These two islands show how barren and desolate the islands can be before they are colonised. The Galapagos Islands are a series of nineteen large islands, nearly fifty small islands, and many submerged sea mounts. Each formed in a conveyor-belt fashion by the Pacific plate slowly moving over the Galapagos hot spot. This hot upwelling of mantle is now directly underneath Fernandina Island at the western edge of the Galapagos islands, with smaller older islands carried to the east by tectonic shift, and the oldest islands now submerged as sea mounts to the far east.

 

Bartolome Island was still at the desolation stage. It was barren and rocky, with only a few pioneer plants (the ones able to live on rock and slowly turn it into soil) and lava lizards living on the island. We were still able to see the lava flows, lava tubes, tuff cones and splatter cones from the island’s birth. The most surreal vision from seeing these same volcanic swirls and loops from underneath the water, with white-tipped reef sharks, sea lions and manta rays gliding over shiny magma coils.

 

Pottering around in the bay on the boat we were able to watch storm petrels hopping on the surface of the water, red swallow tails flying above us, and a solitary Galapagos Penguin sitting on the rocks.

 

After lunch we landed in Sullivan Bay in Santiago. This shelf of the island was only born 120 years ago from a fresh lava flow, so we were able to walk over the tinny metallic surfaces and see the pahoehoe (ropelike formations from rapidly cooled lava) and aa (rough and ragged formations formed as gas bubbled out of the lave during cooling) lava flows. The plain was cracked and buckled due to the expansion of the rock after cooling, and the high iron and magnesium content of the basalt made it feel like we were walking on an alien planet made from contorted steel. Even this metallic bed was not sterile though, with lichens and lava cactus growing in isolated spots and starting the process of breaking the rock down into soil.

Sunday
Jul222007

Sea Lion pups playing

Overnight the board left Santa Cruz and sailed to Rabida, a soothing rocking while we slept. Today was our day to play with Galapagos Sea Lions, an endemic subspecies of Californian sealion. The sealions covered the beaches, basking in the sun, sleeping and kissing. The adults ignored us completely even when we walked within a few feet of them. From close up we could watch the big males exert their dominance with loud grunts and spittle flying from between their sharp fangs. 

The reason for the rich numbers of Galapagos Sea Lions on a few small islands on the equator comes from the Humboldt Current. Named after Alexander von Humboldt, the Prussian naturalist who invented the contour map and first proposed that South America and Africa were once joined, it is responsible for the richness of the whole western South American coast. It is 160km wide and 3000km long. It moves at 3.7km/hour, bringing cold water from the Antarctic, forcing the upwelling of nutrient rich water through the warm but sterile surface. The current is deflected by the bulge of Peru out to the open ocean where it makes it to the Galapagos Islands before dying, providing the rich feeding grounds off the islands. All this changes during El Niño though, when the warm current from the equator displaces the Humboldt current, turning the water off the islands into a sterile desert with the rich water trapped deep below the surface. This forces a collapse in the population of Sea Lions, penguins (lost 77% of their population) and marine iguanas, but an explosion in land iguanas, finches and mocking birds, as the El Nino brings more rainfall for the terrestrial species. Seabirds get a double hit - less fish in the ocean and huge number of mosquitoes on land, driving them away from their nests.
 

The Galapagos Sea Lions and Galapagos Tortoises show the two opposing evolutionary forces that act on the Galapagos Islands. Gigantism is common on islands, as a large body size allows easy gathering of food during rich times and storage during lean times, and predators are few. Yet Bergmann’s Law is the observation that closely related animals tend to be smaller towards the tropics, in order to be able to shed heat easier. So we see animals like the Galapagos Tortoise and Flightless Cormorant, the largest of their types, and the reduced size of the Galapagos Sea Lion (compared the Californian Sea Lion), the Galapagos Fur Seal (the smallest marine mammal) and the Galapagos penguin (the second smallest penguin).

 

 

As well as the sea lions we saw baby Brown Pelicans being fed by their parents, sticking their beaks so far down their parents’ throats that we felt for sure they would be causing real damage. The adults weren’t thrilled about it either, they soon flew off again after being pestered by fledglings the same size as them. We saw American Oyster Catchers (which only became residents of the islands five years ago), hermit crabs, and Frigate Birds. We went for a walk inland into the arid part of the island and saw a solitary Galapagos Hawk sitting on a rock and came to a cove where Sally Lightfeet feasted on a dead pelican down on the rocks below. I then snorkelled with marine iguanas and tropical fish, being surprised when sea lions sprang up in my face and darted away, while Lydia had to stay out of the water as her contact lenses were in her lost luggage.

 

We had a nap after lunch while the boat sailed to James Bay on Santiago. Here the Galapagos Sea Lion pups were feeling particularly frisky. Some spent the time suckling milk or sleeping, but the others wanted to play. Rather than being scared of us, we had to run back when they tried to climb over us or chase each other and us in a game. They came right up to us and investigated our snorkel gear, all the time making extraordinary noises and grunts. I snorkelled again, and this time saw a score of Pacific Green Turtles within a metre of me.

After snorkelling we walked to the other side of the island. On the rocky volcanic shelves we saw dozens of basking marine iguanas, lined up in rows to soak up the sun, in an effort to get warm enough to swim down into the water and collect algae. As the only marine lizards, iguanas are not adapted well enough to life in the water to be able to survive long periods in the ocean to gather algae. It is not breathing that is the problem – when Darwin found the marine iguana he tested its ability to hold its breath by weighting an iguana with an anchor and throwing it overboard attached to a rope. It was still alive when he hauled it up thirty minutes later. Their problem instead is holding enough heat in their body for them to use their muscles to swim back to shore. The young iguanas are forced to take the slim pickings down at the water’s edge, and it is only the large males (who can grow to 1.3m long and 9kg) that can retain enough heat to swim down to 12m to eat the best algae fields. While marine iguanas have not solved the eat problem, they have adapted to the excess salt by concentrating it in small glands by the nose and constantly sneezing it out while sun baking, so standing next to the rows of marine iguanas we got splashed with small puffs of brine. Interestingly, marine iguanas and algae actually represent an inverted food pyramid, with the biomass of marine iguanas greater than that of the algae they eat, because the algae are able to grow so fast in the rich waters that the biomass added per unit of time is great enough to support the large population of marine iguanas. In order to survive the El Niño, when the sterile warm waters stop the algae from growing, the iguanas are able to resorb their bone mass and shrink by up to 20%.

Close by the marine iguanas were a few sea grottos where Galapagos Fur Seals hid in caves. The Galapagos Fur Seal is actually a sea lion that evolved from a parental species that lives on the southern tip of South America. Evolved to withstand great cold, it is in danger of overheating on the equator, so unlike the Galapagos Sea Lions which bask on the beach, it hides in sea caves during the day and hunts for fish at night.

That night we had many cocktails on board our boat, with a fun party in the Galapagos.

Saturday
Jul212007

The Origin of Species

 Our Frequent Flier had time zone confusions, so we were up an hour early for our flight to the Galapagos. We flew from Quito to the island of Baltra, where we drove to the ferry to cross onto Santa Cruz. Just during the ferry transfer we saw Brown Pelicans, Galapagos Sea Lions, Sally Lightfeet and Red Billed Tropic Birds. We drove across Santa Cruz to board our boat, watching marine iguanas and Sally Lightfeet bask on the rocks, Darwin’s Finches flitter around chasing flies, Brown Pelicans watching Blue Footed Boobies dive deep into the water for fish and a Great Blue Heron idly picking at the seaweed.

We were in the amazing Galapagos Islands, made famous by the 1835 voyage of the HMS Beagle. Charles Darwin was invited on the Beagle as gentleman company for Captain Robert FitzRoy, and was not the official naturalist. When he first saw the islands he wrote "nothing could be less inviting than the first appearance". The islands are most arid and barren, volcanic outposts. They are also actually extremely poor in biodiversity, as only a few species have been able to reach and thrive on the islands. In fact, over the past 3.5 million years since the oldest island formed only 400 colonisation events have occurred, one every 12 000 years. The rate may be even slower than this, genetic testing shows that marine and land iguanas are 15 million years apart, therefore they either represent separate arrivals or they arrived 15 millions years ago when none of the current Galapagos Islands had formed and the sea mounts reached the surface.

Instead of being rich in biodiversity, the Galapagos are rich in endemics as the long isolation allows each arrival species to evolve to their new environment. We saw the most famous endemics that afternoon, when we drove across Santa Cruz to the moist highlands to see the Galapagos Tortoises. The tortoises were large and still. Enormous rocks with a prehistoric face hiding under the shadows or reaching out on a veined and wrinkled neck. They reminded me of the skeksis from The Dark Crystal, with a cruel vulture beak and dead grey skin. While they sat like boulders in the mud, when they started to move they looked like implacable tanks.

There are two types of Galapagos Tortoise, the Dome-shelled tortoises of the cool moist highlands, and the Saddlebacks of the low arid lands. Each has evolved to its environment. The Dome-shelled is larger (with shells over a metre long the males reach 300kg) and they have short limbs, to be able to keep their heat better. The Saddlebacks are smaller (around 50kg on average) and have long limbs and a saddle on their shell so their neck can reach up higher. This allows them to be able to reach up high and eat the Opuntia, a type of cactus that has evolved into tree-like proportions, and it also gives rise to the name “Galapagos”, Spanish for “saddle”. While the two types of tortoise live separate lives most of the year, in order to lay eggs the female domed tortoises need to descend to the lowlands to lay their eggs. Galapagos tortise eggs become male if they are incubated under 28.5 C and female if they are incubated above 28.5 C, so if the females stayed in the cool highlands all the eggs would hatch into males.

As well as being shaped by the islands, the Galapagos Tortoise has altered the islands in return. The Opuntia has grown so tall in order to escape the Saddleback, reaching far greater heights on islands that have the tortoise. The Galapagos tomato seeds now need to spend time in a tortoise’s digestion system before they can germinate.

There were once 14 different subspecies of tortoise. Over 100 000 tortoises were harvested by sailors because they were easy to collect and they could be kept alive on deck without food or water for months, giving them fresh meat throughout the voyage. This harvesting drove three subspecies extinct. A fourth might be extinct; there is only one Pinta tortoise – Lonesome George. He is only 90 years old and he could easily live for another hundred years, so they are searching for another Pinta tortoise on other islands, but genetic testing indicates that he may actually be an Espanola tortoise, making the Pinta extinct. The other 10 subspecies are now healthy. The Espanola tortoise dropped down to fourteen individuals, but captive breeding and release has built the numbers up to over 1000.


As well are Galapagos tortoises we watched Golden Warblers bathe, and saw some of Darwin’s Finches, egrets and the introduced Ani. There are fifty one species of land birds in the Galapagos Islands, with a very high proportion (43%) being endemic – twenty two endemic species and three endemic subspecies. The proportion of endemics is even higher when the thirteen vagrant species (observed once, but not colonised) are counted out, 66%. The observed vagrant species show that while colonisation events are improbable, they do occur. Yet the 22 endemic species represent only seven different colonisation events – a rail, a hawk, a dove, a martin, a flycatcher, a mockingbird and a finch. Two endemic owl subspecies, the Barn Owl and Shorteared Owl, came from two separate colonisation events. The expansion of a well suited immigrant is reflected by the success of goats on the islands. In 1959 two females and one male were released on Pinta. By 1970 the population had expanded to 100 000 and it took until 1986 to eradicate them.

Not all vagrants are so lucky though, it was only those vagrants that reached the islands in large enough numbers at the ideal time that were able to flourish. The ones that did diverged from the mainland populations, as the islands are far enough away that additional individuals arriving to keep up gene pool flow is extremely unlikely. Because the small islands are close enough that most birds will travel in between them, almost all endemic successes have stayed as a single species (with flightless reptiles the story is very different, with seven separate endemic species of lava lizard, six endemic species of gecko and three endemic snakes on different islands). The mockingbirds (separated into four species) and the finches (separated into thirteen species) are the exceptions to this rule, for different reasons. The mockingbirds are very reluctant to fly across water, so the four different species and two subspecies are all found on separate islands, with travel rare enough to allow geographical divergence.

 

The finches were different. Unlike the other colonisation species they have highly specialised diets, so to take advantage of an array of unexploited food sources they had to diverge by adaptive radiation. So the finches show different species living together on the same islands, but with beaks adapted to unique food supplies. On every island with more than one finch species, the finches have at least a 15% difference in beak size, with small and large forms to specialise in different food supplies, while the same finch species on islands with only a single finch tend to have medium-sized beaks to inefficiently take advantage of a variety of foods. The larger islands that support multiple Finch species show a very high level of divergence in eating behaviour, with seed eaters, blood drinkers (the Vampire Finch pecks Boobies to draw blood to drink, and kicks eggs against rocks to break them), insect eaters and tool users (the Woodpecker Finch breaks off spines from cacti to delve under the wood to find beetles). Interestingly there is actually a fourteenth species of Galapagos Finch, the Cocos Island Finch, which was seeded onto the Cocos Islands from the Galapagos and not from the mainland.

While these finches are one of the most striking examples of adaptive evolution, Darwin didn’t actually include them in “The Origin of Species”. The finches all look pretty much the same (we certainly couldn’t spot the difference) and he thought they were just variants of the one species. It was only when he brought his specimens back that a specialist told him they were separate species, and he saw how only evolution could adequately explain their existence. Unfortunately his finch collection was poorly labelled and he wasn’t sure which were from which islands, so he played it safe and left them out of the book, concentrating on the mockingbirds.

After watching the tortoises and finches we walked down a hollow lava tube, the long winding tunnel caused by the surface of a lava flow solidifying while the centre flowed on, and then had a cocktail in town before heading back for our first night on the boat.