With the waters around the Galápagos offering such riches, it is not surprising that the islands are home to a great abundance of seabirds, and most famous amongst these are the boobies.
Boobies
The blue-footed booby is a real character and certainly one of the most colourful Galápagos birds. Part of its appeal is its unquestionably clown-like appearance. Yet, in spite of its googly eyes and wondrously coloured, apparently oversized feet, at sea it is transformed. When a squadron of a hundred or so blue-footed boobies homes in on a shoal of anchovies, each bird hauls in its wings, faltering for a moment in mid-air before pivoting to face the ocean, and then plummets. The speed and unwavering direction are impressive. The splashless entry into the water, as after a perfectly executed Olympic dive, has the effect of breaking up the shoal. As the booby swims back to the surface, it’s relatively easy to pick off isolated fish silhouetted against the bright sky.
Between these extremes of comedy and anatomical perfection, there’s been a fair bit of fascinating research into the breeding ecology of these birds, and their striking feet are planted firmly at the centre of the story. When it’s time to breed (between June and August), males and females forge a bond based on the blueness of their feet. As with most other birds—think peacocks—it’s the male that’s particularly showy. Not only are his feet a deeper, brighter blue than the female’s, but he makes a special effort to show them off, flying into his territory with his pedal extremities splayed in contrast against his bright white underbelly. Once he’s done enough to attract a female, the putative pair will engage in an exaggerated foot-raising exercise, each bird flapping from one webbed foot to the other. As things get really serious, the boobies go in for ‘sky-pointing’, when one of the pair (usually the male) stretches its neck and bill towards the sky, extends its wings to the sides and lets out an evocative cry, rather like a mournful blast on a Peruvian panpipe. The birds will also bring each other twiggy little offerings in a symbolic nest-building ritual, swinging the gift up and around before placing it near the other bird’s feet.
Why so much emphasis on feet? A very neat and simple experiment gives us some clues. Cross-fostering is a standard trick used by zoologists in an effort to disentangle the influence of genetic and environmental factors on phenotype (a catch-all term that translates, roughly, as ‘what an individual is like’). In 2002, researchers working with blue-footed boobies on an island off Mexico created a colony of unwitting foster parents. When an egg hatched in one nest, they swiped the chick and swapped it with another of a similar age. So all the booby pairs they toyed with had the same number of chicks; it’s just that one of them was not their own. This set-up allowed the researchers to demonstrate that the colour of the caregiving male’s feet seems to have an influence on chick condition: the gaudier the feet of the foster father, the faster and fatter his chicks will grow.
The most likely explanation for this is that the blueness is an honest indicator of fitness, a badge of quality, an unforgeable certification of health. What does foot colour reveal? At least a couple of things. First, it communicates something about the male’s nutritional status. We know this because if a male blue-footed booby is deprived of food for just forty-eight hours, the colour will rapidly drain from his feet. This is because he’s no longer getting the natural carotenoid pigments from his diet that he uses to gloss his feet. Give him back his food, and the colour will flush back into them in a matter of hours. Second, foot colour may also reveal something about health. When researchers injected males with a low-level challenge to their immune system, their feet got progressively duller over the course of the infection. The reason for this is that carotenoids play a role in stimulating the immune system. Only males in fine fettle can afford to channel these valuable compounds into their feet.
If you’re a female blue-footed booby, then it would make sense to go for the most colourful male you can. He is feeding well and disease-free, he may pass on some of his innate hunting talents or immune strength to your chicks and he is likely to provide well for them as they grow. The researchers confirmed that females pay attention to this trait with another nifty little trick: just after the female had laid her first egg, they took makeup (a ‘non-toxic and water-resistant blue’) to the feet of half the males in their sample, turning their feet from vivid aquamarine (the most attractive) to a pale blue (considerably less desirable). The other males acted as controls.
The faded males didn’t seem to notice their change in status but continued to display and court their partners much as they had been. The females, however, were not so ambivalent. They suddenly reduced the frequency of sky-pointing, symbolic nest building and sex. That’s not all. When females paired with these painted males came to lay their second eggs, they were of significantly smaller volume with significantly smaller yolks than those laid by partners of the controls. The conclusion is clear: a female booby will keep a beady eye on the colour of her partner’s feet, using it to constantly reassess the value of their relationship and her investment in it.
But is this just about females choosing males? Before we move on from blue-foots to consider the two other booby species in the Galápagos, we need to address the fact that female boobies also have blue feet (though admittedly not quite as garish as those of males). In the same way that nipples are a developmental—if redundant—exigency in male mammals, so the biochemical shenanigans that male boobies use to convert dietary carotenoids into bluish pigments might just be something females must put up with. Alternatively, males might be exerting some kind of choosiness themselves. Why not? In most bird species, females are notable for their drab appearance and absence of elaborate sexually selected traits. But in those species where males contribute substantial amounts to the breeding effort—as in the blue-footed booby, for instance—one might expect males to be a bit more discerning about whom they mate with.
In a follow-up study that showed an admirable absence of gender bias, the booby researchers sought to find out, repeating the makeup experiment but this time painting the feet of females rather than males. Lo and behold, males pay attention to a female’s foot colour too. Dulled-down females received much less attention from their partners—and indeed from other males in the colony. It’s all in the feet. If they are bright blue, verging on green, the bird is likely to be happy, healthy and attractive. If they are pale blue, almost white, then it’s struggling.
The Nazca booby is a less comical spectacle, an altogether snazzier bird with a white glossy body and a Zorro-like mask around its eyes. Is it hiding something? Those ornithologists who’ve taken a good look at its behaviour have discovered it is. Nazca boobies lay two eggs, the second as insurance against the failure of the first. But when both hatch, the first chick to do so—let’s call her A chick—wastes no time in attacking her younger sibling, forcefully ejecting B chick from the nest. Because the Nazca female lays its eggs several days apart, A chick has a distinct size advantage, and the greater that advantage, the quicker A chick is to expel its diminutive sibling. Unfed and unprotected, B chick faces certain death, its corpse destined to be hoovered up by a hungry frigatebird or other scavenging beast.
This is not all. Nazca booby society holds an even darker secret. For some reason, juvenile females suffer higher mortality than males. The result is there are many more adult males than females. Those males that can’t find a partner get up to something really nasty, wandering through a colony in broad daylight in search of unguarded Nazca nestlings (a fairly common sight once they reach around one month of age and their parents begin to go on extended foraging trips). In around one-third of instances, the unemployed adult will behave rather nicely to the chick, standing beside it, preening it or even presenting it with gifts of twigs, pebbles or feathers. More often, though, the adult will abuse the youngster, jabbing at it with its bill, plucking out its down or biting it and shaking. Occasionally, these advances are sexual too, the aggressor climbing onto the chick’s back and squashing it beneath its feet as it attempts to mate.
Apart from the emotional trauma caused by this abuse (at which we can only guess), the nestlings may suffer an injury and, as a result, can die. A red scratch or gaping wound is hard to conceal against such brilliant white fluff, and mockingbirds will peck at a nestling’s wound to top up their diet with some nutritious Nazca blood. Perhaps the most startling finding is that those boobies bullied as chicks are more likely to go on to torment nestlings as adults. In an extraordinary paper published in 2011, the Nazca researchers referred to a ‘cycle of violence’, a phrase usually reserved for discussions of child abuse in humans. Their findings, they concluded, ‘provide the first evidence from a nonhuman of socially transmitted maltreatment directed toward unrelated young in the wild’. When I first visited the Galápagos in 2003, I found the Nazca more attractive than the blue-footed booby. Now I’m not so sure.
In contrast to the blue-footed and Nazca boobies (which are only found in the eastern Pacific), the red-footed booby can be found throughout the world’s major oceans. But in the Galápagos it has a peculiarly limited distribution. This may have something to do with its food of choice—flying fish—which means it’s sensible to set up home on the peripheral islands of Genovesa, Wolf and Darwin with good access to the deep sea. However, there may be another reason too. The red-foot’s foraging trips can take parents away from the nest for long periods, with nestlings typically left unattended for over ten hours every day. Being so vulnerable to the depredations of the Galápagos hawk, the red-footed booby has only been able to establish itself on islands where the hawk is absent. Indeed, the disappearance of hawks from San Cristóbal and Floreana (owing to the human presence there) seems to have allowed red-footed boobies to establish new colonies on these islands.
Juvenile red-foots appear to be particularly playful, sometimes gathering in large flocks of around one hundred birds and engaging in what’s been described as ‘a curious communal game’. Working on Wolf in the 1980s, a pair of ornithologists observed the booby game on several occasions and described its rules: ‘The game, if we may call it so, always started near the summit of the island.’ From their observation point the scientists could not quite see what the birds were playing with (‘it might be a feather, a leaf or a stick’), but one individual would kick off proceedings by dropping the ‘toy’ into the cloud of birds below. ‘After a few seconds of free fall it is caught by a second bird and carried upwards, only to be dropped again and subsequently picked up by yet another bird.’ The game would finish when the wind had carried the flock out to sea and the toy had fallen onto the surface. On the same expedition, the ornithologists also noted several peculiar objects (‘3 short plastic thongs, 1 toy soldier and 1 toy bassoon’) beneath the nesting and roosting spots of the red-footed boobies. ‘Are these the boobies’ “toys”?’ they wondered. ‘How else can these strange objects make their way to the top of Wolf Island?’ How indeed?
Galápagos red-footed boobies are also notable for the fact that most individuals are brown (apart, of course, from their crimson boots, their blue bill infused with pink and the inky stain around their eyes). A quick survey of populations elsewhere reveals that white-feathered red-foots are by far the most common, making up around 95 percent of the global population. But there are also a few populations—as in the Galápagos—where brown is the dominant hue.
This is the sort of pattern that would have fascinated Darwin, and it has caused a good deal of head scratching amongst red-footed booby researchers. We now know that the brownness in Galápagos red-footed boobies is caused by a couple of mutations in a single gene—that encoding the melanocortin-1 receptor (small variations of which are known to cause dramatic changes in pigmentation). But is there something more interesting going on here? Is it possible that brown boobies are at some kind of advantage over white boobies in the Galápagos? Perhaps the darker feathers offer some kind of thermoregulatory benefit? Maybe brownness plays an important role in pairing, rather like the blueness of the blue-footed booby’s feet. Perchance it provides the birds with some kind of camouflage, helping them to sneak up on their prey. Or what if, as has been suggested for brownish red-foots that live on Europa (a small island in the Mozambique Channel between continental Africa and Madagascar, not the smallest of Jupiter’s four Galilean moons), the brown makes them less susceptible to avian bullying by the likes of frigatebirds? We don’t yet know.
Frigatebirds
In the Galápagos, there are two species of frigatebird: the great and the magnificent. These can be pretty hard to distinguish, though the great frigatebird is the smaller of the two, and its adults have a greenish tint to their feathers rather than the magnificent frigatebird’s purple gloss. The youngsters, often perched patiently in a scrubby nest of twigs, are easier to tell apart: the chest and neck of a great frigatebird juvenile tends to be rust stained, whereas an immature magnificent has a more vulturous look, its white chest and head standing out against its otherwise dark plumage. Just why these youngsters take so long to reach full-blown adulthood (at least eight years for a great frigatebird female and around ten years for a male) remains a bit of a mystery. But the development of adult plumage appears to proceed in fits and starts, sometimes with no moult for up to four years. This suggests that perhaps these birds face an internal energy crisis, unable to gather sufficient food to afford the expense of refreshing their feathers. This is why many of the juveniles have a distinctly ragged, rather unsavoury look about them.
Both great and magnificent frigatebirds have huge wings relative to their body size. This might make for an awkward lolling gait and an ungainly, flapping take-off, but once airborne it allows them to stay aloft for long periods, cover great distances and reach speeds of around one hundred miles per hour. Their deeply forked tail gives extraordinary manoeuvrability, helping them to snatch at flying fish or scoop squid from the ocean’s surface without entering the water (as they’d struggle to get airborne again). These aerial acrobatics also mean they can dabble in kleptoparasitism (thieving to you and me). A frigatebird often looks out to sea from its thorny perch, keeping a jet-black eye out for incoming traffic: red-billed tropicbirds, terns, boobies. When it spies a suitable target, it attacks. For the seabird returning from its feeding grounds, the sensible thing to do is to regurgitate a morsel of half-digested fish, which is usually enough to divert the attacker from its offensive so as to pluck its winnings out of the air. If nothing is forthcoming, however, the frigatebird will strike, its hooked bill grasping the victim’s tail or wing to encourage it to release some of its catch. These assaults can be brutal, with both birds dropping out of the sky and the smaller bird coming away with damaged feathers or, worse, a broken wing.
During their troubled adolescent years, it can be rather hard to tell a male from a female frigatebird. But once a juvenile finally graduates to adulthood, it becomes a doddle to separate the sexes: both great and magnificent frigatebird females are marked out by their neat, understated white bib; the males go in for far more garish attire, an astonishingly crimson, turkey-like wattle they can inflate to the size of a football. Like the blue-footed booby’s feet, this is clearly a signal that females pay attention to. This is especially obvious in a frigatebird colony during the breeding season, when males thrust out their wings, throw their heads to the sky and pump up their throats. It’s not just the sight that’s impressive; the sound is too. These courting birds begin to click, uttering a deep staccato that resonates inside their ballooning necks. The sight of dozens, sometimes hundreds, of such males showing off to females in a concentrated spot is reminiscent of what zoologists refer to as a lek, a mating ritual where females browse the wares on offer, mate with the most attractive male, then head off to rear the offspring as a single parent. But unusually for species with such ostentatious males, both great and magnificent frigatebirds form male-female partnerships, and males make a substantial contribution to the breeding effort.
Why, then, do males go to all the trouble of producing a fancy wattle and spend day upon day trying to impress the ladies? It probably has something to do with the balance of males and females. In one study of great frigatebirds on Tern Island in the middle of the Pacific, researchers found that amongst unpaired birds, there were typically two or three males (and sometimes up to ten) for every female. It remains unclear why this is so. Perhaps the sex ratio is somehow skewed at birth. Perhaps females are more likely to die. Or perhaps, with their greater overall investment in reproduction, not all females in a population can afford to breed every year. Whatever the reason, it looks like the extraordinary puffed-up courtship of the male frigatebird is a price worth paying for a chance of some seriously scarce action. It certainly seems to work. Those males that can afford to do the most displaying have a significantly greater chance of ending up in a meaningful relationship with a member of the opposite sex.
So far, none of the seabirds we’ve looked at is peculiar to the Galápagos. Eagle-eyed as ever, Darwin made this observation himself, noting far higher levels of endemism amongst the land birds than the seabirds. The explanation is simple. As a general rule, seabirds travel further than land birds and tend to move in groups, so they will have found it relatively easy to reach the Galápagos and settle without much disturbance, as Darwin put it, to ‘their mutual relations.’ There are, however, several notable exceptions, seabirds that have now become completely tied to the Galápagos, found nowhere else on earth.
The Albatross
One of them is the waved albatross, a colossal bird with wings that span more than 2m from tip to tip. The only place visitors can reliably encounter this species is at Punta Suarez on Española, one of the most popular visitor sites in the Galápagos. From the dock at the eastern tip of the island, a trail winds up onto the eroded flat top of the island, which acts like a runway for the albatrosses, allowing them to build up speed before launching off the island’s sheer southern perimeter. In fact, waved albatrosses have even colonised a bona fide but abandoned landing strip on the island, cleared during World War II to service a US radar base.
En route to the albatrosses, we’ll just take a short digression to consider a couple other stunning (though not endemic) seabirds on show at Punta Suarez. Red-billed tropicbirds can be seen nesting in rocky crevices beside the tourist trail or cruising just off the island, their impressively long tail streamers steadying them against the prevailing south-easterly wind. It’s also a good place to see swallow-tailed gulls, a beautiful bird with black tips to its wings, a slate-coloured head and what looks like a dab of white paint on its bill. They are also unusual amongst gulls for being nocturnal, a disposition discovered in the 1960s by a dedicated researcher who spent several nights sleeping rough on South Plaza (where there’s also an active colony of these gulls). He set an alarm to wake him on the hour every hour so he could see what the gulls were up to. At dusk, he found, the birds began to leave the colony en masse so that by the time it was dark, the only individuals left on land were those incubating eggs or brooding chicks. By feeding at night the swallow-tailed gull may be sidestepping the competition, able to forage undisturbed by larger, more aggressive seabirds like boobies, frigatebirds and albatrosses. They are also probably after particular prey species that come to the sea surface at night, as they prefer to forage during a full moon, when the abundance of these creatures is greatest. The swallow-tailed gull’s bright-orange eye ring is wide, exposing a relatively large area of the eyeball to its environment and helping it to see in the dark.
Back to the endemic waved albatross. Between January and March, most of the birds are at sea. But from April onwards they begin to return, males first to stake out an area of clifftop and await the return of their long-term partners. These bonds between males and females are reaffirmed every year in a ritualized ceremony. Females lay a single egg between April and June but concentrated in May, usually on a flat patch of ground or beneath a bush. In the first few days of incubation, one or the other of the parents may move the egg, shuffling it along on top of its feet as emperor penguins do during the Antarctic winter. There’s an obvious risk of breakage during such a manoeuvre, so there has to be a good reason why they do this. Nobody has really come up with a satisfactory one. Perhaps they’ve taken a dislike to a neighbour. Over the next two months, the male and female will share the burden of incubation, with one coming and the other going. This becomes more frequent as hatching approaches, with switching occurring every four days or so. Then an awkward chick emerges, with patchy brown down eventually puffing up to give the youngster a fluffy, daffy air. The parents will brood the young chick for several weeks, followed by a slightly more relaxed guard for a couple more, before they are prepared to leave it alone for days on end.
Owing to the size of the albatross, it’s relatively easy to fit one with a satellite transmitter to find out where they go. When researchers did this in the 1990s, they found that the waved albatrosses head towards the coastal waters of mainland Ecuador and Peru. The signal from one bird was picked up more than 1,200 km from the Galápagos, at a latitude level with Lima.
FIGURE 3.1. The waved albatross. The courting ritual of this elegant seabird is an intricate affair, captured in these sketches by Frederick Peabody Drowne in October 1897. ‘They have a manner of fencing with their bills that is ludicrous and remarkable,’ wrote Charles Harris, chief naturalist on the expedition. Reproduced from Walter Rothschild and Ernst Hartert, Novitates Zoologicae 6, no. 2 (1899): 7–205; see Drowne’s entry for 26 October 1897.
Once the chick is strong enough to be left alone, it stands a good chance of surviving. Still, there’s a lot of death amongst these hatchlings, with only around one in four breeding females rearing a chick to the point of fledging. Over the course of this chick-rearing phase, juvenile birds hatched in previous years start to return, and in November and December the colony reaches a crescendo of behaviour, with plenty of interactions between birds and courtship displays between existing pairs and wannabe breeders. This involves an impressive range of movements, from what looks like deferent head bobbing and circling, to jaw gaping and snapping, to a rapid rapier-like exchange of bill clacks, to a plaintive lowing thrown to the sky.
The Penguin and the Cormorant
In contrast to the waved albatross, with its long-distance movements, two other endemic seabirds do not fly: the Galápagos penguin and the flightless cormorant. The most suitable place for these species to feed and breed is in the productive west, between Isabela and Fernandina. Even then, they face similar pressures to the fur seals and sea lions. In the particularly harsh El Niño of 1982–1983, for instance, when fur seals and sea lions were so hard hit, only one in four penguins and cormorants survived.
For both the penguin and the cormorant, the unpredictable arena that is the Galápagos has had several consequences. The Galápagos penguin is famously small, with adults weighing in at just 2 kg, about half the size of their closest living relative, the Humboldt penguin from Chile and Peru. Only with its diminutive stature and relatively thin feathering can a bird most commonly associated with colder climes hang on so far north. The flightless cormorant, by contrast, seems to have grown in stature (it has more than twice the body mass of its closest living relative, the neotropic cormorant of Central and South America), possibly to improve on its capacity to dive. Whereas all other species of cormorant are pretty nifty swimmers, the flightless variety’s heavier frame and more powerful feet mean that, for a given depth, it can stay down for longer. This shift away from flight could never have happened in a world full of predators. But in the Galápagos, where the only land-based threat to the flightless cormorant comes from the Galápagos hawk, the costly flight apparatus—large flight muscles, huge wings—was essentially redundant. ‘I believe that the nearly wingless condition of several birds, which now inhabit or have lately inhabited several oceanic islands, tenanted by no beast of prey, has been caused by disuse,’ wrote Darwin.
FIGURE 3.2. The Galápagos penguin. This species is famously small, with adults weighing in at just 2 kg, about half the size of their closest living relative, the Humboldt penguin from Chile and Peru. Reproduced from Osbert Slavin, Transactions of the Zoological Society of London 9 (1877): 447–510.
As with much else in the Galápagos, the capricious conditions mean that the penguin and the cormorant must also be flexible when it comes to breeding. If the waters on the western edge of the archipelago are too hot (greater than 24°C to be precise), there simply won’t be enough food for the penguins to breed. If the waters are cooler (22°C or lower), food will likely be sufficient, but breeding is still costly. Once they have put on enough weight, penguins will come ashore to moult, shedding old feathers and growing new ones. This takes between ten and fifteen days to accomplish, during which time they will not feed and may lose as much as a quarter of their body weight. Once a pair has located a suitable nest site, preferably one that’s sheltered from the equatorial sun’s egg-frying glare, the female will lay one egg (or a second if there’s a lot of food to be had). If conditions take a turn for the worse, they will abandon first one of the chicks and then, if things get really bad, the other.
For cormorants, breeding is an even more intriguing affair. For most bird species, females typically invest more in reproduction than males, so are particularly choosy about whom they mate with (see blue-footed boobies and frigatebirds above). For the flightless cormorant, the roles are somewhat reversed. Although there is no way for the female to get around the cost of producing eggs (she’ll typically lay three in a single reproductive event), she is far smaller than the male and, as a consequence, has pared down most of her other maternal duties to a minimum. It’s the male that must build the nest, usually a fancy arrangement of seaweed harvested from the seabed. It’s the male that brings most of the food to the newly hatched chicks. It’s the male that’s best able to keep predatory hawks away from the brood. And once the chicks have fledged (after a couple of months), it’s the male that’s left in the lurch when the female abandons him and her young offspring to go in search of a new partner. In a whimsical world, this is the female’s way of increasing her chances of reproductive success. It might not seem particularly fair on the male. But it works.
If living off the oceans is a risky business, it doesn’t come much easier on land. Let us leave the waves, the currents, the fish, the marine mammals and the seabirds and look to the rocky shoreline of the Galápagos. It is time to think about plants, where they came from, how they got here and how on earth they managed to survive.
