How do swallow-tailed gulls mate?<\/h2>\n
Nesting can happen at any time of the year, provided food is abundant \u2013 the birds are asynchronous breeders, meaning they don\u2019t stick to a fixed reproductive season. As a result, while colonies are never empty, not all birds are present at any given time. Each pair has its own breeding cycle of 9\u201310 months, roughly half of which is spent raising a single chick.<\/p>\n
The remainder is spent far from the Gal\u00e1pagos, mainly off the coast of Peru, in the heart of the Humboldt Current, with the birds never making landfall. This is when their dapper black hoods moult to white, and the bright red rings around their bulging round eyes fade away. When they are ready to nest, they moult again, regaining all those contrasting colours, ready for their return to the archipelago.<\/p>\n
As nocturnal hunters, returning to their nests before dawn, swallow-tailed gulls tend to spend their days quietly. They doze through the hottest hours, with just the occasional territorial scrap interrupting the peace. Only when the sun dips below the horizon does the colony come to life, the birds\u2019 drawn-out screeches serving as signals for small flocks to lift off and head for the far horizon.<\/p>\n
How do they hunt?<\/h2>\n
These nightly hunting forays aren\u2019t random searches for food, as might be the case in other scavenging gulls. The swallow-tailed\u2019s favourite prey items are squid and deep-sea fish, elusive sea creatures that rise from the ocean depths in the dead of night in search of plankton.<\/p>\n
Various other comings and goings take place in the darkness, with parent birds exchanging incubating and chick-guarding duties. Night-time on land is dangerous even for a nocturnal gull, as short-eared owls, which have equally good vision, prowl the colony for vulnerable youngsters. Other potential predators include larger gulls, hawks and herons.<\/p>\n Sunrise marks a new hubbub of activity, and this is my favourite time to observe a colony. The birds pay no attention to my presence, and I can watch them for hours, pondering the many secrets their lives still hold.<\/p>\n Pairs will be variously courting, building nests from tiny pebbles or fragments of coral, engaging in protracted mating rituals, or feeding their chicks regurgitated squid. Often, panic will break out when a marauding frigatebird attempts to steal the catch, with neighbouring birds joining forces to form a screaming, whirling, defensive mob.<\/p>\n Parents take it in turns to brood their single egg or nestling, and might delicately preen each other\u2019s facial feathers in a gesture of tenderness. In a courting pair, the female will sometimes \u2018beg\u2019 like a chick, peeping with her head low and beak upwards. An attentive partner will respond by regurgitating an entire squid for her.<\/p>\n Every so often I am left utterly incredulous by the gigantic size of some of the squid that are served up to both partners and chicks, already partially digested. How these birds manage to catch such hefty creatures in total darkness, and haul them all the way back to shore in their distended stomachs, is anyone\u2019s guess.<\/p>\n There is still a lot we have to learn about the swallow-tailed gull but, in recent months, remarkable research has uncovered tantalising new insights, piquing my interest in these birds all over again. A study using tiny satellite-trackers, led by ornithologist and Gal\u00e1pagos native Sebasti\u00e1n Cruz, has demonstrated that this is the only known seabird that actively prefers to fish on the darkest nights.<\/p>\n Cruz and his team discovered that the swallow-tailed gull has a flexible sleep schedule, adjusting its activities in response to the lunar cycle. The brighter the moon, they found, the less the birds were absent from the colony. The pattern suggests that swallow-tailed gulls forage at sea when normally deep-dwelling prey are most abundant at the surface, feeding in the darkness to avoid detection.<\/p>\n Interestingly, Gal\u00e1pagos fur seals schedule their foraging activity in a similar manner: like the gulls, they rely heavily on nocturnal squid.<\/p>\n The study also found that swallow-tailed gulls roam far and wide on their night-time foraging trips. Tracking individual birds travelling from distinct colonies to known feeding grounds far out at sea, the researchers revealed that the gulls were exceeding distances of 100km per night.<\/p>\n It\u2019s an incredible new finding \u2013 though just how this species manages to hunt and travel in pitch darkness, in a way that is completely different to other members of its family, is still not fully understood.<\/p>\n Look carefully at a swallow-tailed gull and there are some clear adaptations that enable its night-hunting behaviour. Most obvious are the enormous eyes, equipped with bulbous, light-gathering lenses and a tapetum lucidum \u2013 a layer of reflective tissue behind the retina that bounces the light back a second time, magnifying its intensity.<\/p>\n There\u2019s also the colour of its \u2018pecking spot\u2019, located at the tip of the beak and serving as a guide for chicks begging to be fed. In most gull species this is bright red or yellow, but in the swallow-tailed, it\u2019s white. For a species that returns to the nest under cover of darkness with its catch, paler markings are much easier to see.<\/p>\n Earlier research has also reported certain features that, at the time, were not necessarily seen as relating to hunting technique \u2013 for example, the bird\u2019s buoyant flight. Compared to other gull species, the swallow-tailed\u2019s wings, particularly its primary feathers, are longer and highly flexible, as is its widely fanning tail. These features provide exceptional manoeuvrability in mid-air, an obvious asset when snapping at squid that skip only briefly out of the water.<\/p>\n Occasionally, when I\u2019ve used a torch on a boat at night, hunting gulls have flown into the beam, revealing entire undersides in a remarkably reflective white. Watching squid leap from the water and the birds in hot pursuit, I couldn\u2019t help but wonder if those flashing white wings, even when illuminated only by stars, could be sufficiently disruptive to flush prey into the air.<\/p>\n Finally, there is that strange crackling call, something between a rattle and a creak. Intriguingly, it reminds me of the sound that dolphins make underwater. Could it be that the swallow-tailed gull, along with all its other unique characteristics, is also the only seabird to somehow use echolocation to detect its airborne prey?<\/p>\n While echolocation \u2013 in which an animal can \u2018visualise\u2019 its surroundings by interpreting a sound as it bounces off surfaces such as the sea \u2013 is a widespread navigational tool among bats, it is rare in the avian world, known only from cave-nesting oilbirds in the South American rainforest and some swiftlets, who likewise inhabit dark caverns.<\/p>\n Sebasti\u00e1n Cruz recently embarked on a new study using tiny sound recorders temporarily attached to the hunting gulls. Originally sceptical about the possibility of seabird echolocation, he was excited to discover that the swallow-tailed gull emits at least two types of click pattern \u2013 a simple volley and a complex burst.<\/p>\n The regular volleys seem to correspond to some form of echolocation, while the rapid-fire bursts are more typically associated with a focused \u2018read\u2019 of a moving object. The latter may be connected to those squid-chasing episodes that I myself have witnessed, though of course we can\u2019t be sure.<\/p>\n Next on Sebasti\u00e1n\u2019s agenda is an expedition at sea, recording the bird\u2019s vocalisations while using only infra-red cameras to rule out the potential effect of a ship\u2019s lights, which have been a factor during my own observations. I\u2019m excited to see what more his team will learn about the hunting adaptations of this enigmatic bird.<\/p>\n There are more than 50 species of gulls worldwide, from the Arctic to the Antarctic, and from the high Andes mountains to the open seas.<\/p>\n Anyone who simply thinks of \u2018seagulls\u2019 (a misnomer, as they are collectively called gulls, not seagulls) as those raucous and pesky sandwich-robbers at a beach picnic is sorely mistaken. None could be further from that characterisation than the mysterious, elegant swallow-tailed gull \u2013 which is, at last, starting to give up some of its secrets.<\/p>\nSwallow-tailed gull behaviour<\/h2>\n
Why do they hunt at night?<\/h2>\n
What do they look like?<\/h2>\n
What makes the swallow-tailed gull unique?<\/h2>\n