Thu, 19 Jan 2023
— A lot more than meets the eye.
As a child growing up in the then-remote Galápagos Islands, the birds that surrounded my island home — unafraid as they were — fascinated me. Before long I had learned to recognize every species with ease, but it was their oft-surprising behavior and specialized natural history that truly captured my imagination. While the total number of resident species may be modest (73, including two introduced ones that turned wild), their uniqueness and extraordinary adaptations — to both land and sea — make their evolution and life histories far more fascinating than their mere identification. How they live and what they do at times can be truly startling, and for over 50 years now, this is what I’ve focused both my photography and my personal observations upon.
It isn’t necessary to be an expert researcher (or a birder, book in hand) to identify a Blue-footed booby. But what is actually far more interesting than the color of its feet is the extraordinary techniques these birds use for their precision diving, sometimes plunging from on-high like arrows, at others slicing through the surface horizontally by skimming the wavetops, depending on their prey.
It is useful to know that the only way to distinguish between male Magnificent and Great frigatebirds in the field relies on the purplish, versus greenish, metallic sheens on their respective backs.But how many people realize that their feeding habits are totally different? While the Magnificent frigate is a coastal scavenger, the Great hunts the high seas, snatching flying-fish on the wing, when these are flushed into flight by other marine predators.
Frigatebirds have the largest wing-surface to body-weight ratio of any bird alive. In fact, their hollow bones are so lightly built that an individual’s complete plumage, when taken separately, actually weighs more than its entire skeleton. Despite spending most of their life at sea, frigatebird feathers aren’t waterproof like other seabirds’, so they perform virtually all life functions — except breeding — on the wing: feeding, preening, bathing, sleeping, molting. Some use tropical thunderheads as natural elevators, circling within the cloud to rise up to 8,000 ft, from where they can cover huge areas of ocean without exerting a wingbeat.
Unique traits among Galápagos birds span both land and sea.For example, while many of the world’s seabird species range widely, using vastly dispersed island groups to nest, in contrast, a full 11 of the 18 breeding Galápagos seabirds are endemic at either species or subspecies level.This includes the rarest gull in the world, the Lava gull, with a stable population of around 500 individuals.
Flightless cormorants are the largest in their family, having traded flight for unrivalled diving abilities (recorded as deep as 230ft), and spending their entire lives within a few miles of their natal colony, a range they share with the second smallest and only truly tropical penguin, also endemic to Galápagos. The Swallow-tailed gull, (see my previous blog about the two endemic Galápagos gulls) on the other hand, has turned away from the land, and with enormous eyes adapted for nocturnal hunting, flies far out into the Humboldt Current as far south as offshore Peru, as does the Waved albatross, the only truly tropical member of the world’s 22 recognized species of these largest of all seabirds.
Even some of the more ordinary-looking Galápagos seabirds, which were once thought to be wide-ranging, have been recognized as endemic species upon closer examination, like the endangered Galápagos petrel and the Galápagos shearwater (left), perhaps the commonest yet least noticed of all species. The enigmatic White-vented (or Elliot’s) storm petrel (right) is the smallest of all seabirds, weighing as little as half an ounce, yet its nesting sites remain a complete mystery to this day.
Unsurprisingly, however, it is by far within the land bird group that isolation has resulted in the highest degree of evolutionary divergence, as well as behavioral innovations. All but one of the 30 residents in this group (not counting two feral introduced species) can be found nowhere outside of Galápagos. While the most cryptic — and third flightless species after penguin and cormorant — is the secretive Galápagos rail (below right), the most brilliantly colorful of them all is also endemic: Darwin’s flycatcher (sometimes referred to as the Galápagos vermilion flycatcher, below left) which could only be mistaken, at a glance, not with another bird species, but with a red hibiscus flower!
Identification for many Galápagos land birds is simple.If it’s a dove, it must be the Galápagos dove. If it’s a mockingbird on Española Island, it’s an Española mockingbird; likewise for San Cristobal Island. But how fascinating to then discover that these birds often live in family clans, where younger generations support their elders, closing ranks in territorial defense.
Or the Galápagos hawk (the only fully diurnal resident raptor), where the opposite happens: juveniles are evicted by their parents as they mature, so all the immature birds on a given island flock together in a roaming band of several dozens to overwhelm territory holders by their sheer numbers.
And while the mere glimpse of a bright yellow songbird can bring the certainty of a Yellow warbler sighting (endemic subspecies), less well known is the fact that this adaptable passerine regularly bathes in seawater tidepools
Behavioral surprises abound among Galápagos birds. Flightless cormorants practice sequential polyandry. Females (smaller than males) frequently begin a new breeding cycle with a different male while leaving their previous mates to provide food on their own for their growing chicks. The hawks too often use a polyandric strategy, but in this case, it is the female who is the larger partner, sharing a year-round territory with up to eight males, all of whom share equal hunting duties and mating privileges in a long-term, stable relationship.
Last but not least, come the 17 species collectively known as Darwin’s finches, who break all traditional bounds of identification and biology, and do so on many fronts. Deriving from a single ancestor (a wayward tanager of some sort, geneticists tell us), evolution and adaptation have played some funny tricks in isolation.
In practice, this means that the keen birder must first divorce him or herself from the tried-and-tested notion of color as the main identification feature: with plumages varying from beige through mottled grey, to black, or mixtures thereof, the birds’ colors might at best narrow down the options to genus level, but not species — in actual fact, plumage shades more accurately reflect age and sex of the individual.Likewise for the colors of legs (all of them black), or beaks, which can vary all the way from pale yellow to completely black, reflecting only age and reproductive status, but definitely NOT the species!
The only remaining tools for the identification of Darwin’s finches are the shapes and sizes of their respective beaks (in themselves highly variable within species). Often more helpful than visual ID is a process of elimination regarding the location of the sighting, since a number of species inhabit just a single island. Even the birds’ songs are confounding, with a high degree of variation from place to place, and even more so from island to island, in the case of the more widespread species within the archipelago. Indeed, while studies have shown that the strongest reproductive barriers between species may be the songs that are passed on from fathers to sons, hybridization is quite common.
Evolutionary studies of Darwin’s finches, as so meticulously demonstrated by Drs. Peter and Rosemary Grant, have highlighted some truly astonishing abilities to adapt and change in response to environmental factors within just a few generations. This leaves the observer to ponder whether these innocuous small birds, rather than representing an evolutionary conundrum that defies the accepted rules of character displacement (where similar species living together tend to diverge from each other), in Galápagos we may be seeing something totally different. Could it be that here is an evolutionary system that works on the basis of a sort of ‘genetic melting pot’, where crisscrossing genetic material can serve to re-amalgamate traits as and when variable environmental conditions offer them a selective advantage?
Finally, if evolution — and therefore the individual identification — of Darwin’s finches can present a few headaches, their inventive behavior is second to none in the bird world: Little birds that attack much larger birds to drink their blood, and also roll their eggs down steep rocks to break them and drink their contents; birds that select, shape and use twigs and cactus spines as tools to hunt insects; birds that elicit a collaborative response from giant tortoises and iguanas to enable them to eat their ticks; birds that specialize in puncturing cactus flowers and fruit; birds with big beaks and small beaks, and massive beaks, and thin beaks, each one used cleverly for its own special purpose.
These
easy-to-carry pocket guides
are available
in Galápagos shops.
For the careful observer, the joys of birdwatching in Galápagos are endless.
