Gulls are also seabirds, as many of them do spend a significant part of their lives at sea, despite what those of us who live by the sea attest.
But when we speak of seabirds from a birder point of view, we tend to mean more those birds whose names evoke the scent of nautical mile upon mile of crystalline brine and the skin-reddening whip of wild winds: fulmars and frigatebirds; gannets and guillemots, pelicans, petrels, puffins; skuas, auks, and albatrosses.
they live in colonies numbering upwards of a few dozen to some in their millions
Collectively there are around 350 bird species who depend on the marine environment for their survival. Whilst there are vastly different types of birds who are classed as a seabird, they all experience the same environmental and feeding challenges.
A few things that they all have in common is that they are usually the apex predator of the niche they occupy, they tend to live longer than most “land” birds, they dedicate a significant part of their lives – around six months – to their young, and they live in colonies numbering upwards of a few dozen to some in their millions.
The one common characteristic that all seabirds share is that they feed in salt water. Because so many of them digest salt water whilst feeding and of course drinking, they have developed a salt gland next to their nasal cavities that helps regulate their blood and organ water content, and this gland secretes almost pure sodium chloride.
Seabirds also almost always have webbed feet to help them manage the forever moving surface of the water or for propulsion when diving.
With a few exceptions, all seabirds have far more feathers protecting their bodies than land birds, and these are almost always waterproof. This dense plumage not only protects many birds from getting wet, but insulates against the cold winds.
Opting for function over form, seabird plumage is usually drab and neutral, with variations on a theme of black, white and grey (save for a few species like the penguins and birds known as tropic birds).
These slate grey and dark tones above provide excellent camouflage against aerial predators, so much so that the US Navy adopted the colour of Antarctic prions for their battleships.
White underbellies provide the protection from monsters of the deep below, mimicking the daylight, blending the bird in with the sun’s glare or the clouds.
their plumage is not waterproof, so if the get wet, they become waterlogged and drown
Many seabirds take their sustenance from just beneath the surface, with a few resorting to diving. Marine currents often bring food such as krill, fish and squid to within reach of a submerged beak.
Depending on the species, surface feeders will either skim as they fly or dip as they settle on the waves and swim down a short way.
Storm petrels even “dance”, pattering and hovering just above the water’s surface, and some birds like the frigatebird never land in the water, as they would be unable to get airborne again – their plumage is not waterproof, so if they get wet, they become waterlogged and drown.
Not so great for a seabird. Quite why a seabird evolved to be vulnerable to getting wet is not entirely understood, but there is always a counter to a flaw – the primary diet of frigatebirds is flying fish and flying squid.
These birds have adapted to have the largest wing surface area for their body weight of any bird, weighing just one kilogram and having a wing span of two metres.
Their exceptional eyesight and ability to soar and glide at speed makes it far easier for them to spot and reach the feeding frenzies of tuna and dolphins from four metres above the waves; the fish and squid trying to evade the jaws of the submerged predators take to the air and, unfortunately for them, usually then end up leaping directly into the mouth of the frigatebird.
Seabirds who dive for their food have a greater area in which to feed, but their ability to do so often comes at a cost to other functions – loons and grebes walk with extreme difficulty, penguins can’t fly, and auks are very inefficient fliers.
Shearwaters, however, can dive to considerable depths and maintain long distance flight; the short-tailed shearwater can dive below 70 metres (230 ft). Of all the pursuit divers, the most efficient fliers are the albatrosses, but they are the poorest divers.
Gannets, boobies, tropicbirds, some terns and brown pelicans are all plunge divers, diving into the water from flight, which uses less energy than pursuit diving by using the momentum of the dive to override the pressure of all that air trapped in their feathers trying to keep them buoyant.
However, for this they need clear waters so that they can see their prey from the air. If this is lacking, they will usually keep watch like the frigatebirds for dolphins hunting and pushing shoals towards the surface.
The gang's all here
As mentioned, feeding at sea has inhibited many birds from having good mobility on land, so they make their nesting and breeding grounds as inaccessible as possible to land animals – remote islands or outcrops, craggy headlands and sheer cliffs.
It is also thought that seabirds live in colonies to share information – the sea is very big and the food is very small, and often hidden beneath an undulating mirror.
Colonial behaviour has these advantages but they can also sometimes be their downfall – disease can spread disastrously quickly, and adverse weather events can often take out great numbers, with burrows flooding and cliff nests being scattered to the maelstrom below.
Just because seabirds live in hard-to-get places, it doesn’t mean that nothing can get them, and a colony of tightly-grouped birds are vulnerable to devastating attacks from other airborne species, having nowhere else to hide.
Crest of the heatwave
It’s an axiom of our times that birds are the perfect indicators of the planet’s wellbeing. The marine environment covers more than 70% of the world’s surface; it influences the climate and weather patterns, and anywhere between 50-80% of our atmosphere is generated and maintained by the photosynthetic lifestyles ofoceanic plankton (one particular species, Prochlorococcus, is the smallest photosynthetic organism on Earth, and produces up to 20% of the oxygen, more than all of the tropical rainforests combined).
Marine mechanisms are still poorly understood, despite or because of the fact there’s so much of it to research, so scientists look to the behaviours, breeding cycles and success or failures of seabird populations as to how well the seas are doing. And the signs aren’t looking good.
it’s the scale of the temperature climb that has got many worried
We are getting more familiar with heatwaves at home each year; the same is also true of the marine world. Some of us may recall the emergence of something along the Pacific coast of North America termed The Blob – an unusual and large mass of relatively warm water that came to being in late 2013 and eventually dissipated in 2016.
At 1,000 miles long and wide, and 300m deep, it was 2.5°C / 4.5°F warmer than normal. Warm waters carry far less nutrients than the cold upwellings, which means less phytoplankton, therefore less zooplankton, therefore very little food for those near or at the top of the food chain.
Between the summer of 2015 and the spring of 2016, 62,000 dying or dead emaciated common murres washed up on the western seaboard beaches of America.
Studies found that they had all died of starvation, and as ocean currents typically only bring a fraction of the birds who die at sea ashore, it’s thought there could have been a million more lost beneath the waves. Two thirds of them were adults, which then went on to have an impact on breeding populations.
Heatwaves are normal occurrences at sea, but it’s the scale of the temperature climb that has got many worried, and their frequency is increasing, too.
Since the emergence of The Blob, scientists have been scrambling to comprehend the mechanisms and repercussions of marine heatwaves, and you can read a collection of current research and models here.
As with all things, climate change, biodiversity threats and knock-on effects are intertwined like seaweed through a rusted shipwreck.
Pulling it apart is time-consuming so, in the meantime, all most of the world can do is firefight. But the work being done to anticipate marine heatwaves is picking up pace, and many hope that if we can predict when they are coming, steps can be taken to mitigate the inevitable effects;stop fishing here or there and allow populations to recover, focus breeding efforts here or there to boost numbers again, store or farm seeds, corals or other plants in less vulnerable regions to then replace what has been lost, and so on.
The ocean-going birds of the world may be out of sight for so many of us, but they should never be out of mind. The health and existence of seabirds is critical to understanding the waters that provide the wind to the sails of our world, and to weather the coming storm, we need to listen out for the seabird’s cry.