Seabirds are a class of birds that are adapted to marine environments. It can be said that their subsistence depends on the sea. There are many kinds of seabirds with peculiar customs and colorful colors and shapes, so we invite you to learn more about them by reading this article.
sea birds
You will be able to realize that they are very different from each other, regarding lifestyle, customs, behaviors and physiological aspects. By studying them you will realize that among them there are cases of convergent evolution, because they have evolved with similar adaptations to difficulties of the same nature, especially in relation to environmental and food problems.
The first seabirds are known to have evolved in the Cretaceous period, although modern families originated in the Paleogene. A general characteristic of seabirds is that they tend to live a long time, their sexual maturity and reproduction occur later than in land birds, and fewer young individuals are observed in their populations, which require more time and dedication from adults.
Many of these species establish their nests in colonies, which can be of various sizes, from a dozen birds to millions. Some species are known to carry out extensive annual migrations, thanks to which they may have to cross the equator or in many cases they can circumnavigate the Earth.
They have many methods to obtain their food. Some can do it on the surface of marine waters and others can do it in its depths, and even with each other. We can find that there are coastal or pelagic species, while others may be completely far from the sea in some periods of the year.
As far as the morphology of seabirds is concerned, we will say that this is due to many causes. We can take for example the symmetry of the body of the birds, which is established by the type and the activity that they must carry out during the flight, and which can be grouped into categories such as hunting, mobilization to nesting places or reproduction and migration.
The body mass of an average seabird is about 700 g, the wingspan is about 1,09 m, and the total area of the wings is 0,103 m2. But these measurements will depend on elements such as the flight mechanism and the etiology of the species.
The chronicle of the relationship between seabirds and human beings is very extensive. They have always provided food for hunters, provided guidance to fishermen on their way to their fishing grounds, and guided sailors to the shores. Due to the fact that many of these species are at risk due to the activities carried out by human beings, they are taken into account by movements in favor of environmental conservation.
Classification
We will begin by indicating that there is no single scientific conceptualization by which it can be established, without a doubt, which groups, families and species are seabirds and most of those that exist are, to some extent, arbitrary definitions. The name seabird does not have any taxonomic value; it is just a kind of grouping, somewhat artificial, that is not used by scientists in their classification.
It could even be thought that it is a form of traditional or colloquial taxonomic classification, since it includes multiple taxonomic groups, but excludes some species. Or as two scientific specialists in the field, EA Schreiber and J. Burger, have said, it is about designating them by the characteristic that all seabirds have in common and that is that they feed in seawater, but, as occurs in other biological claims, some of them don't.
Traditionally, all the sphenisciforms and procellariiforms have been classified as seabirds, along with all the pelecaniformes, with the exception of the aningids and some caradriforms, composed of the stercorarids, lárids, sterids, alcids and rhynchopids. It is usual that phalaropes are also included, because, despite the fact that they are wading birds, two of their three species are oceanic for nine months a year, during which they cross the equator and feed in the open sea. .
Gaviforms and podicipediforms, which do not nest in lakes but spend the winter in the sea, are classified as waterfowl. There are also some mergynes within the family Anatidae that are truly marine in winter, but are excluded by convention from this group. Many waders and herons could be considered marine, because they live on the coast, but they are not classified that way.
Evolution and fossil record
Due to the fact that seabirds have to spend a large part of their lives in sedimentary environments, that is, in environments in which there is almost permanent sedimentation, they are well represented in the fossil records. It is known that they arose in the Cretaceous period.
It is known that the Hesperornithiformes belong to that period, which are a group of non-flying birds, which are similar to loons, which could dive in a similar way to these, and loons, which use their legs to move under water, although this family had a beak with sharp teeth.
Although it seems that the Hesperornis do not seem to have left descendants, the first modern seabirds also had their origin in the Cretaceous period, with a species that has been called Tytthostonyx glauconiticus, and that seems to be related to the procellariforms or the pelecaniformes.
In the Paleogene, the oceans were dominated by the first procellariids, which were giant penguins and two extinct families, Pelagornithidae and Plotopteridae, which were a group of large birds similar to penguins. The modern genera began their great dissemination in the Miocene epoch, although the Puffinus, which includes the modern maned shearwater and sooty shearwater, are from the Oligocene epoch.
The greatest variety of seabirds seems to have occurred in the late Miocene and Pliocene period. At the end of the latter, the oceanic food chain underwent a great transformation due to the global extinction of a large number of species, and then came the expansion of the number of mammals in the sea, which hindered the fact that seabirds recovered its ancient diversity.
Features
It can be said that seabirds have many characteristics that are common to them, but they have many more that are different, as many as the number of species that can be found, because each one has something in particular, so we are going to make an approximation to the characteristics of seabirds, depending on various perspectives:
For its Adaptations for Maritime Life
Cormorants, like the long-eared cormorant, exhibit a unique layer of feathers, which allows less air to pass through, but still absorbs water. This versatile adaptation makes it easier for them to thermoregulate and combat natural buoyancy.
Seabirds have multiple adaptations to be able to live and take their food in the sea. The morphology of their wings is due to the era in which they evolved, in such a way that, by observing them, a researcher can learn information about the way they behave and their way of feeding.
Long wings and low wing loading are typical features of pelagic species, while birds that can dive tend to have shorter wings. Species such as the wandering albatross, which finds its food on the ocean surface, have a lower powered flight and depend on a type of glide that has received the name of dynamic, because in this type of glide, the wind is deflected by the waves, which makes it possible for the bird to rise, as well as the possibility that they glide down or down. ascent.
Some petrels, alcids and penguins have wings that are conducive to moving underwater and, in some cases, such as the latter, they do not have the ability to fly. These birds are prepared to dive up to 250 m and are capable of storing oxygen, either in air sacs or through the myoglobin in their muscles.
Penguins have a larger blood volume, which makes it easier for them to store more oxygen. By the time they dive, they can also cause their heart rate to slow down and deliver blood only to the organs that are vital.
In general, seabirds have webbed feet, a fact that allows them to move easily on the surface of the water and, in the case of several species, they are useful for diving. Procellariiforms have an unusually strong sense of smell for a bird, and they use it to find their food in large expanses of the ocean, and probably also to find the places where their colonies are found.
The supraorbital glands have the function of helping seabirds to osmoregulate and eliminate the salt they ingest when drinking and feeding, especially when they feed on crustaceans. The excretions of these glands, which are located in the head, exit through the nasal cavity and are composed almost exclusively of sodium chloride, although concentrations in small amounts of potassium and bicarbonate can also be found, along with a minimal portion of urea.
These glands are under the influence of the parasympathetic nerve and can be stopped with anesthesia and drugs such as carbon dioxide inhibitors. This is an essential adaptation, because the kidneys of these birds are not capable of processing and eliminating very high concentrations of this substance; and while it is true that all birds have a nasal gland, it is not as developed as that of cormorants or penguins.
In fact, seabirds have supraorbital glands ten to one hundred times larger than those of land birds, because their size is related to the amount of salt to which the birds are exposed. Hyposmotic regulation, that is, the conservation mechanism of organisms that live in conditions of extreme salinity, also occurs through the reduction of flows that are excreted, as is the case of urine, which is reduced to prevent water is lost.
With the exception of cormorants and some terns, and similar to most birds, all seabirds have plumage that is resistant to water. But, if we compare them with the species of birds that live on land, they have more feathers, in order to better protect their body.
As a consequence of the density of their plumage, it is what prevents the bird from getting wet, while the cold is avoided because they also have a thick layer of down. Cormorants have a unique layer of feathers, which allows less air to pass through and therefore absorbs water. Thanks to this adaptation, they can swim without fighting against the buoyancy caused by retaining air between the feathers, but they also retain the enough of this to prevent them from losing too much heat when in contact with water.
The plumage of most seabirds, which is limited to black, white, or gray color variations, is less conspicuous than that of land birds. tropical or some penguins, but the greatest color is found in the beaks and legs.
Seabirds have a camouflage function due to their plumage as a form of defense, the color of the Antarctic duck-petrel, which is the same color used by the battleships of the United States Navy, reduces its visibility at sea; and the lower white part that many species possess may have a function that helps them hide from prey. The fact that the tips of their wings are usually black, due to melanin, helps them to avoid deterioration and friction on the feathers.
Diet and feeding
Seabirds evolved to be able to obtain their food from the seas and oceans. If they are observed carefully, it will be possible to verify that their physiology and behavior are designed according to their diet. Their living conditions have caused species from different families and even different orders to develop similar strategies in the face of the same difficulties, which is an excellent example of convergent evolution. This can be seen in the convergence between penguins and alcids.
It has been established that seabirds have four basic feeding strategies in the sea: feeding on the surface, chasing food by diving, diving, and preying on larger vertebrates. Of course, within each of these categories there are numerous variations.
surface feeding
In general, seabirds obtain their food from the surface of the ocean, because the currents tend to concentrate food such as krill, forage fish, squid and other prey that they will have within their reach using only the head sinking strategy.
In turn, this method can be classified into two: surface feeding during flight, which is what petrels, frigatebirds and hydrobatids do; and feeding while swimming, as occurs with fulmars, gulls, various shearwaters, and petrels.
In the first category we will find some of the seabirds that have a more acrobatic style. Some take snacks from the water, as frigatebirds and some ternids do, and others scamper and circle on the surface of the water, like some hydrobatids. Many of them don't even bother to land on the water, and some, like frigatebirds, find it difficult to take flight again if they do.
Another type of seabird that does not land to feed is the Rynchopidae, which have a unique method of hunting that involves flying close to the surface with their jaws in the water, which automatically close when their bills touch something. Its beak reflects its unusual lifestyle because the lower jaw is longer than the upper jaw.
In this group we can find that many of the birds that can swim also have unusual beaks, adapted to a specific prey. The genera Pachyptila and Halobaena have beaks with filters called lamellae, with which they are able to filter plankton from the water they drink. Many albatrosses and petrels have hook-shaped beaks, which makes it easier for them to hunt their prey, when they move fast.
Gulls are seen to have less specific beaks, indicating a more opportunistic lifestyle. In the province of Buenos Aires, the seagulls benefit from the fisheries and consume young specimens of anchovy and yellow croaker. The kelp gull is, within the laridae family, the one with the widest trophic spectrum; Olrog's gull is rather a specialist. Everything will depend on the lifestyle of the seabird.
pursuit dive
This type of practice is the one that exerts the greatest harassment on seabirds due to its functions and its evolutionary patterns, but the reward is being able to have a larger feeding area than those of those birds that stay on the surface. They are capable of executing propulsion movements underwater with the help of their wings, as in the case of penguins, alcids, pelecanoids and some species of petrels, or with the help of their legs, such as cormorants, loons, loons and some types of fish-eating ducks.
In general, those that can be propelled with their wings are faster than those that can be propelled with their legs. But in both cases, using their wings or feet for diving has limited their usefulness for other activities: loons and loons walk with great difficulty, penguins can't fly, and alcids have sacrificed flight efficiency instead. favor of diving
For example, the razorbill requires 64% more energy to fly than a petrel of the same size. Many shearwaters fall somewhere between the two because they have longer wings than typical jet-powered divers. their wings, but greater wing loading than other procellariids that obtain their food from the surface, which makes them able to dive to considerable depths, while allowing them to travel large areas more efficiently.
Within this family, the best diver is the Tasmanian shearwater, which has been recorded swimming 70 m under the sea. Several species of albatross also have the ability to dive, although to a limited extent; the sooty albatross reaches depths of 12 m. Of all the divers that pursue their prey, the most efficient in the air are albatrosses, and it is no coincidence that they are the worst swimmers.
In polar and subpolar climates, diving is the most common way of foraging, since it is not energetically viable in warmer waters. Because they lack the ability to fly, many diving birds are more restricted to their foraging area than others, particularly in the breeding season when nestlings need to feed regularly and abundantly.
plummet
Gannets, boobies, fetontiformes, some ternids and the brown pelican dive from the air. This is very useful, because it allows them to use the energy of their momentum to overcome natural buoyancy resistance, which is caused by air trapped in their plumage, and use less energy than other divers.
In this way they can consume the food elements distributed more widely, especially in the case of impoverished tropical seas. In general terms, this is the most specialized method of hunting that exists among seabirds; other more versatile birds, such as gulls and skuas, use it, but with less skill and from lower heights.
Brown pelicans take years to fully develop the dexterity required to master the dive; once they have matured, they will be able to dive from a height of 20 m above the surface of the water and adjust their body before impact, to avoid any damage. It has been claimed that this group of birds can only hunt in clear water, as this would allow them to have a better view of their prey from the air.
Although this method is predominant in the tropics, the link that has been established between this technique and the clarity of the water has not been solidly established. Some species that use this strategy, like surface-feeding birds, have relied on tuna and dolphins to move schools to the surface.
Kleptoparasitism, carrion and predation
Within this very broad category of feeding strategy, other strategies of seabirds that are located in the next trophic level are included. Kleptoparasites are seabirds that normally feed on the food of other birds. In particular, frigate birds and skuas make use of this technique, but also gulls, terns and other species opportunistically steal food.
The habit that some seabirds have of nesting at night has been understood as a way to get away from the pressure exerted by air piracy. Normally, this behavior becomes habitual in the breeding season of the chicks, when the parents have to carry food to the nests and are hindered by young adults, faster than older birds.
It has been proven that kleptoparasites have the ability to select their victims very well. However, kleptoparasitism does not play an essential role in the diet of any species, rather it is a nutritional supplement obtained through hunting.
The result of a study on the way in which the common frigatebird steals food from the masked gannet concluded that the former was able to obtain, in the best of assumptions, 40% of the food it needed, but that on average it only scored 5%. Many species of gull feed on the carrion of birds or marine mammals when given the opportunity, as do giant petrels.
Some albatross species also feed on carrion: an analysis of squid beaks revealed that many of the squid eaten by albatrosses are too bulky for the birds to have caught alive, and included intermediate-deep water species , which is out of reach of these birds.
We can find seabirds that also feed on other seabirds, such as seagulls, skuas and pelicans, which sometimes prey on eggs, chicks and young adults from nesting colonies. In turn, giant petrels can take prey the size of little penguins and seal pups.
Lifecycle
The lives of seabirds are very different from birds that live on land. In general, it can be said that they are strategists, they live longer, between twenty and sixty years, delay their mating until they are ten years old and invest more effort in a smaller number of offspring. Several species only have one clutch per year, unless you lose the first. Unless that happens to a bleak mowl and to many species, such as procellariiforms or sulids, which only lay one egg per year.
Seabirds have the habit of caring for their young for a very long time, which can last up to six months, one of the longest breeding periods among birds. One of these cases is that of the common guillemot, since, although their chicks shed feathers, they remain next to their parents in the sea for several months.
Frigatebirds are the birds that exercise the most parental care, with the exception of a few birds of prey and the southern ground hornbill, a species in which the chicks fledge after four or six months and then remain under the tutelage of their parents until for fourteen more months. Due to the extended period of care for their young, reproduction in these birds occurs every two years, instead of annually.
This extreme duration of the reproductive cycle of life is possibly an evolution in response to the disadvantages of marine life, among which is hunting prey that is widely dispersed, as well as the frequency with which reproduction failures occur, due to unfavorable marine conditions and inherent lack of predators compared to land-dwelling birds.
Due to the greater effort involved in raising the young and because, on occasions, finding food means traveling far from the place where the nest is located, in all marine species, with the exception of phalaropes, two parents take part in the care of the chicks and the pairs are monogamous, at least for a season.
Some species of seabirds, such as gulls, alcids and penguins, remain in the same mate for several seasons, and many species of petrels do so for life. Albatrosses and procellariids, which mate for life, take several years to form a pair bond before going on to have offspring; albatrosses perform a very elaborate courtship dance, with various techniques, which is part of the formation of this bond.
Ecological niches in seabirds
You can see the fact that different species of seabirds live together in the same habitat where food is not enough, which is why they must change their eating habits so that they can survive in that place. This ability to specialize their food is known to scientists as an ecological niche.
A group of researchers at the Max Planck Institute for Ornithology in Radolfzell, Germany, has learned just how flexible ecological niches are. Discovering that the habits with which diving seabirds carry out their predation are very different, in terms of time and place, even within the same species, as well as in the case of different species.
It has also been concluded that ecological niches are not inflexible, and not only suffer the effects of the different characteristics that each natural habitat of seabirds may present, but are also affected by the need that birds have to hide from their predators. and to avoid the possibility of having competition between their neighbors, and also give rise to different modes of behavior within the same species.
Seabirds are very suitable species to investigate because they are animals that share a limited food supply in their habitat. Seabirds have to live on land during their breeding and breeding season, and during this time they are forced to share space and food with many other birds.
It has already been said that the chicks are reared in nesting colonies, often located in places that guarantee the birds protection from their predators. But we must take into account that the place where the food is found is located mostly in coastal waters. Therefore, the birds must separate from their colony to get food and be able to return to the colony to feed the chicks.
In one of the Malvinas Islands, a team from the Max Planck Institute for Ornithology was able to observe in detail the hunting habits of four diving seabirds. Studies show that seabirds of different species, as well as colonies of the same species, differ in their temporal and spatial distribution, and seek their food in different areas of the sea, often very far away, and at different temperatures and depths.
The ecological niches of the species studied are much less rigid than previously observed. It was concluded that the few changes in the area in which they live, in their behavior, or the requirement to avoid predators and antagonists, help to consolidate this type of specialization.
Nesting and colony formation
Studies have determined that 95% of seabirds live in colonies and that these are among the largest aggregation places for birds in the world. Colonies that have more than a million individuals have been documented, both in the tropics, as occurs in Kiritimati, located in the Pacific, and in the polar latitudes, which is the case of Antarctica.
These very large groups have almost exclusively the purpose of nesting. Whenever they are outside of the mating season, non-breeding birds will try to locate themselves in areas where there is the greatest amount of prey.
The organization and disposition of the colonies is very changeable. It is possible to get nests made individually, separated by spaces from each other, as in an albatross colony, or concentrated nests, as in a guillemot colony. In most of these settlements several species may nest, usually visibly separated by some niche differentiation.
Seabirds can nest in trees, if any, in plants, as they sometimes build their nests in them, on cliffs, in underground burrows and in rocky crevices. It is normal to observe that there is great competition between birds of the same or different species. Aggressive birds such as sooty terns are sometimes able to drive less dominant species out of more desirable nesting areas.
In the winter period, the petrel avoids competing with the Pacific shearwater, because the latter is very aggressive. At times when mating seasons overlap, Pacific Shearwaters are capable of killing young petrels in order to use their burrows.
Many seabirds maintain nesting site fidelity and use the same hiding place, nest or settlement for periods that can extend for several years and aggressively defend that territory from rivals. This behavior increases the chances of their reproductive success, provides a suitable place for couples to get together and reduces the effort of having to search for a new place.
However, re-searching may have good mating results, provided the new terrain is productive. Usually, young adults mating for the first time return to their natal colony and build their nests near where they hatched. .
The capacity possessed by seabirds, which is called philopatry, is so powerful that research on Laysan albatrosses established that the average distance between the hatching site and the place where a bird established its own territory was 22 m; another study, this time on Cory's shearwaters nesting near Corsica, established that nine out of 61 young males returned to mate in their natal colony and established their nest in the hiding place in which they grew up, even two mated with his own mother.
Philopatry apparently favors mating success and influences mate choice in the case of the Cape gannet and the Australian gannet. Colonies are located on islands, cliffs, or headlands, in areas where mammals have very difficult access. They possibly choose their mating grounds based on the protection that the landscape features can offer; furthermore , seabirds are clumsy on land.
Coloniality is seen in birds that do not defend their foraging areas, such as swiftlets, which have a highly variable food source, and perhaps that is why it is seen so frequently in seabirds. Another likely The prerogative is that colonies can act as information gathering places, where seabirds heading out to sea to feed can learn what prey is available by observing their returning mates.
On the other hand, among the drawbacks is that the colonies can have the negative effect of rapidly spreading diseases. Another negative aspect is that they quickly attract the attention of their predators, mainly other birds. Many species are forced to take special precautions, such as returning to their nests at night, in order to avoid predation.
Immigration
Like other species, seabirds have a habit of migrating after the mating season. Of all, the journey made by the arctic tern is the longest, because it crosses the terrestrial equator to spend the summer in Antarctica. Several species also perform trans-equatorial migrations, both from north to south and in the opposite direction.
The group of elegant terns that nests in Baja California separate after the mating season into groups that travel north to the central coast of California, while others travel south to Peru and Chile to stay in the current zone. of Humboldt. Sooty Shearwaters perform an annual migration cycle that rivals that of Arctic Terns. This group of birds nests in New Zealand and Chile and during the summer they move to the North Pacific coasts, such as Japan, Alaska and California, which means an annual journey of 64 km.
Other species migrate over smaller distances from nesting sites and their dispersal in the high seas is determined by the availability of food. If ocean conditions are not adequate, seabirds migrate to areas with better conditions, perhaps permanently if the bird is young.
After they sprout, young birds have a tendency to scatter more than adults and in different areas, so they are often seen outside the normal range for that species. Some birds, such as alcids, do not migrate in an organized fashion, but it is likely that the group may head south as winter approaches. However, some species do not disperse, as occurs in some hydrobatids, pelecanoids and phalacrocoracids, but remain close to their nesting colony throughout the year.
out of the sea
The characteristics of this group of birds indicate that they spend their entire lives in the ocean, many species of seabirds, throughout their lives, reside to a greater or lesser extent inland. Several species reproduce tens, hundreds or even thousands of kilometers away from the coast. Several of these species return to the ocean to feed.
Researchers of seabird life have found nests of snow petrels 480 km inside the Antarctic continent, although they can find very little to eat around those locations. The marbled murrelet nests in old growth forests and it looks for large coniferous branch trees and many branches to build its nest there. Other species, such as the Californian gull, manage to nest and feed in lakes, then go to the coasts in the winter.
Several species of phalacrocoracids, pelicans, gulls and terns never cross the sea, because they inhabit lakes, rivers, swamps, and some gulls live in cities and agricultural land. In these assumptions, it is thought that they are terrestrial or freshwater birds that have marine ancestors.
Other seabirds, especially those that make their nests in the tundra, such as the stercorariids and the phalaropes, migrate by land as well. Other species, such as petrels, razorbills, and gannets, are more restricted in their habits, but sometimes stray from the sea as vagrants. This usually occurs in inexperienced young birds, but also in many exhausted adults when enduring heavy storms, an event known as a wreck, in which many sightings are appreciated by birders.
Relations with the human being
There are many links that unite seabirds with human beings, and in this article we are going to explain several of them:
seabirds and fishing
Seabirds have maintained a long relationship with fishing and sailors, and in it we will find that there are benefits and disadvantages. By tradition, the men who are dedicated to fishing have used seabirds as signalers of the presence of schools, of ocean banks with potential fishing resources and with possible places to anchor and place their nets.
This association of seabirds with land was essential in making it easier for Polynesians to locate small islands in the Pacific. Likewise, these birds have provided food to fishermen far from the mainland, in the same way as bait. Even tied cormorants have been used to catch fish. Indirectly, fishing has benefited from the guano produced by the colonies, because it has the function of fertilizer for the surrounding beaches.
In contrast, the negative effects of seabirds on the fishing industry are limited, in most cases, to the pillage of aquaculture facilities. On the other hand, in the longline type of fishing, the birds steal the baits. There are reports of prey depletion due to seabirds, but, although various evidence of this has been collected, its effects are considered minimal to those of marine mammals and predatory fish, such as tuna.
Several species of seabirds have benefited from fishing companies, particularly discarded fish and offal. For example, the latter make up 30% of the food for these birds in the North Sea and up to 70% of the food in other seabird populations. This can cause other effects, such as the spread of the northern fulmar within the British territory, which is caused in part by the existence of food thanks to discards.
This is a form of feeding that usually benefits surface-feeding birds such as gannets and petrels, but is not helpful to birds that pursue their food by diving, such as penguins.
The fishing industry also produces its negative effects on seabirds, especially albatrosses, which tend to live for a long time and are slow to mate; This is a major concern for conservationists. The bycatch of birds that get caught in nets or hooked on fishing lines has had a strong impact on population numbers.
Albatrosses drown in tuna fishing lines that are set by fisheries that use the longline method. In general, every year hundreds of thousands of birds are trapped and die, which is very worrying, considering He says that several of these species are very rare and peculiar, as is the case with the short-tailed albatross, which has been reduced to 2000 individuals.
According to a study by the National Program of On-Board Observers of the Uruguayan Tuna Fleet, the species that have been most affected by these incidents with longline fishing are the black-browed albatross, the fine-billed albatross and the white-throated shearwater Seabirds are also thought to suffer from the consequences of overfishing.
Exploitation
One of the causes of the decrease in specimens of many species is mainly due to hunting and the collection of seabird eggs, among which are the giant auk and the brilliant cormorant. These birds were hunted for their meat by the peoples settled on the coasts throughout the history of their settlements. In southern Chile, archaeological excavations in middens have provided evidence of hunting by albatrosses, cormorants and shearwaters from approximately 5000 years ago.
This caused several species to become extinct in different areas. Another very alarming fact is that at least 20 of 29 species no longer breed on Easter Island. In the XNUMXth century, the hunting of these birds for their fat and feathers for the hat trade reached industrial levels.
Muttonbirding or shearwater chick harvesting became a major industry in New Zealand and Tasmania, and the Solander's petrel, known in those areas as the providence petrel, became well known for its supposedly miraculous arrival on the island of Norfolk, where it represented a windfall for hungry European settlers.
In the Malvinas Islands, hundreds of thousands of penguins are captured year after year to sell their oil. For a long time, the eggs of seabirds have been an important source of food for sailors who make long voyages; Another cause of increased consumption is the proliferation of urban settlements in coastal areas near a bird colony.
In the mid-XNUMXth century, San Francisco egg collectors managed to collect almost half a million eggs in one year on the Farallon Islands, marking a historic milestone from which the birds have yet to recover.
Unfortunately, hunting and egg collecting activities still persist today, although with less intensity than in previous times, and measures have been imposed for greater control.
An example of this is that the Maori of Stewart Island continue to collect Sooty Shearwater chicks, in the same way they have done for centuries, using traditional methods, which are called kaitiakitanga, to carry out the collection, but today they collaborate with the University of Otago in the study of these populations. On the other hand, in Greenland indiscriminate hunting is placing many species in serious danger.
Other threats
There are other human causes that have led to the decline or extinction of populations, colonies and species of seabirds. Of these, probably the most dangerous is the introduction of other species. Seabirds, who nest particularly on small, remote islands, have forgotten many of their defensive activities against predators.
Feral cats can prey on birds the same size as an albatross, and many introduced rodents, such as the Polynesian rat, tend to steal eggs that are hidden in their burrows. Other introduced species that can cause problems are goats, cattle, rabbits and other herbivores, particularly as birds require vegetation for shelter and shade for their chicks.
Colony disturbances caused by humans is also a big drawback. Visitors, including well-intentioned tourists, can scare adults from their nests, leaving eggs and chicks exposed to predators. There have also been reports of nests being destroyed by visitors.
Several investigations carried out regarding penguins in Argentine Patagonia and New Zealand prove that tourism negatively influences the conditions of these birds. An analysis of the impact of natural tourism on populations of the Long-Eyed Penguin highlighted that the presence of humans on the beaches makes it difficult for adults to find enough food for their chicks, which has a direct effect on their body mass and their chances of survival.
But, the results of another investigation revealed that the Magellanic penguin, which lives in Patagonia, does not leave its nest in the presence of human beings, which seems to establish that it is feasible to make the reproduction of this species coincide with controlled tourism.
A major drawback has been pollution, because it is the cause of the alarming decline of some species. The treatment of toxins and polluting substances is also a great cause for alarm. It is a proven fact that seabirds were victims of DDT until the use of that chemical was prohibited, due to the serious damage it caused to the environment.
Studies have shown that the effects of DDT on the western gull resulted in a population imbalance that caused the pre-eminence of female individuals, problems in the development of the embryo and difficulties in reproducing. In the 90s, the use of this substance also produced serious effects on the Magellanic penguin and the Kelp Gull in the Argentine sea.
Seabirds are also extremely vulnerable to oil spills, as the oil destroys the waterproofing of their plumage, causing the birds to drown or die of hypothermia. Another type of pollution, which is light, also has a detrimental effect on some species, especially nocturnal seabirds such as petrels.
Conservation
The interest in preserving these birds and the protection measures have been implemented since very remote times. In the XNUMXth century, Cuthbert of Lindisfarne had already promulgated what is considered to be the first conservation law for birds in the Farne Islands. Despite this, many species had become extinct by the XNUMXth century, as is the case of the giant auk, the Pallas cormorant or the Labrador duck.
At the end of the XNUMXth century, the first laws for the protection of birds and the first hunting regulations were created that prohibited lead shot, since it had been shown that they had poisoned many birds. Lead poisoning causes anemia severe and of great disorders of the circulatory, immune and nervous systems, as well as causing damage to the liver, kidneys and fertility of birds.
The truth is that lead poisoning can cause death in days or weeks, and has harmful effects on the ability of seabirds to carry out their migration process.
In the United States, the threats facing seabirds are not unknown to scientists in the conservation movement. In 1903, President Theodore Roosevelt decreed that Pelican Island, Florida, would be a national wildlife refuge, in order to protect the colonies of birds that nest there, in particular the brown pelican that nests there. . In 1909 he protected the Farallon Islands.
Currently, many colonies have received protection measures, such as those formed on Heron Island in Australia or on Triangle Island in British Columbia. Ecological restoration techniques have been implemented, in which New Zealand is a pioneer nation, that allow the removal of exotic invaders from islands that are getting bigger and bigger.
Cats in the wild have been expelled from Ascension Island, as have polar foxes from the Aleutian Islands and rats from Campbell Island. The expulsion of introduced species has allowed the number of individuals to increase. of species under threat and even the return of expatriate species has been achieved. After the cats left Ascension Island, seabirds returned to nest there for the first time in more than a hundred years.
Research on seabird colonies has been key to improving their conservation and protecting the spaces they use for their reproduction. In the case of the European shag, which inhabits the Western Palearctic, its migrations are determined by fidelity to a specific site.
Research and studies carried out on the Cíes Islands colony in Spain indicate that, since reproduction is usually more successful when seabirds conquer new places, the criteria for selecting protected areas should not only be based on the number or the size of the populations, but must also take into account the etiology of the species.
In the case of the kelp gull, which nests on the Argentine coast and Patagonia, it is considered very necessary to establish a conservation program that takes into account their mating habits. Likewise, some species of seabirds can act as species sentinel, that is, its health and conservation status serves as an indication of the rest of the populations, this is what happens with the brown pelican on the islands of the Gulf of California, in Mexico.
The conservation status of seabirds in Spain was unknown until the 1980s, when information began to be made public. This despite the fact that in 1954 the Spanish Society of Ornithology was founded. Starting in the 1980s, evidence shows that the situation of birds in Spain improved.
In 2016, the O Grove Ornithological Reserve was created in Pontevedra, Galicia, which is the first in that region. It has marine territories and in it you can find species such as the Balearic shearwater and the European shag. In parallel, in Latin America there are also several initiatives that seek to protect fauna in general and seabirds in particular.
An example of these initiatives is the research that is being carried out in the natural reserve of Gorgona Island in Colombia, or the numerous protected areas in the province of Buenos Aires, in Argentina. But if we truly want to guarantee the conservation of seabirds, their ethology and mating cycles need to be considered.
One of the measures that can be taken would be to reduce the number of seabirds killed as a result of longline fishing, using techniques such as setting fishing lines at night, dyeing hooks blue or placing them under water, increasing the weight lines or use scarecrows.
Over time, more international fishing fleets are being forced to use these techniques. The international ban on net fishing has succeeded in significantly reducing the number of lost birds and other marine animals. In any case, drifting nets, an accident that is often an effect of this kind of illegal fishing, continues to be a serious problem for marine fauna.
One of the projects of the Millennium initiative, which constitutes the previous step to achieve the Millennium Development Goals, which includes what was born in the United Kingdom as the Scottish Seabird Center, which was located near large bird refuges in the Rock Bass, on Fidra and on the islands around it. This area is the habitat of huge colonies of gannets, auks, stercorariids and various other species.
This center makes it possible for visitors to watch live videos taken from the islands and become aware of the threats that affect these birds and how they can be protected. Furthermore, this way of communicating about seabird life has regenerated the image of bird conservation in England.
Another aspect that must be considered is that tourism focused on seabirds generates income for the communities that have their settlement on the coast and gives greater publicity to the way in which the measures for their care should be implemented and respected. An example of this is what happens with the northern royal albatross colony at Taiaroa Head in New Zealand that attracts forty thousand tourists a year.
At the end of the XNUMXth century, the emphasis on the protection of seabirds was followed by that of the conservation of their habitats, which involved the conservation and recovery of lagoons, estuaries, marshes, wintering or resting sites for these birds, and its food resources, through regulations on the status of species that can be hunted and that are not the subject of scientific studies.
Among the international agreements and conventions that exist, is the Agreement on the Conservation of Albatrosses and Petrels, which was ratified by Argentina, Australia, Brazil, Chile, Ecuador, Spain, France, Norway, New Zealand, Peru, the United Kingdom, South Africa and Uruguay; the Bern Convention and the AEWA.
In popular culture
There are several species of seabirds that are little studied and little known. However, some, particularly albatrosses and seagulls, have found their place in the popular consciousness. Albatrosses have been described as the most legendary birds and are associated with a variety of myths and legends.
In the first place, the scientific designation of the family to which the albatrosses belong, which is the Diomedeidae, has its seat in a myth of the defeat of the Argive hero Diomedes and his transformation into a bird. Another example of popular myth is the widespread superstition among sailors that it is bad luck to harm them.
This myth derives from a poem by Samuel Taylor Coleridge called The Rime of the Ancient Mariner, in which a sailor is condemned to carry around his neck the carcass of an albatross he killed.
The second poem that also gave rise to popular myths is the one called The Flowers of Evil by Charles Baudelaire and is called The Albatross (L'albatros), a composition made in three quatrains and in Alexandrian verse; there, the author describes the habit that sailors have of hunting these birds and the consequence that this produces in them, birds that are first so majestic and then so clumsy.
In this last poem, the poet compares himself to an albatross, because his giant wings prevent him from walking. In the creation of popular music this bird also had importance. The 2014 electro house song I'm an Albatraoz, which gained widespread commercial recognition and fame, is based on the story of a woman who identifies with an albatross, as opposed to another, who is named Laurie , which is associated with a mouse.
Gulls are the most well-known type of seabird, as they are often found in man-made habitats such as coastal cities or garbage dumps, and are usually intrepid in nature. Therefore, they also have their place in popular myths.
According to a myth of the Lilloet indigenous people, the seagull was the one who had the obligation to guard the daylight, until the raven stole it, which is closely related to the general symbology of birds, which represent impulses of elevation and spirituality.
We have also found in literature, as a metaphor, as can be seen in the work Juan Salvador Seagull by Richard Bach, or to demonstrate the proximity to the sea, or the way it was used in The Lord of the Rings of JRR Tolkien, both in the insignia of Gondor and therefore Númenor, which was also used in the stage decoration of the film adaptation, and in the song that Legolas sings in the Ithilien forest, in which he reveals his nostalgia for the land to which he will depart, the last abode of the elves.
Furthermore, in Anton Chekhov's The Seagull, an unsuccessful actress who is the main character in the story, Nina, sees an embalmed seagull and esteems it as a symbol that she does not quite understand; this representation is a prolepsis of the suicide of the one in love with her, who in the play was the playwright Tréplev. The seagull in this literary piece can be a representation of madness and freedom.
But it's not just about the albatross or the seagull. Many species have also served as a source of inspiration for humans. Pelicans have long been associated with mercy and altruism, based on a myth in early Western Christian religion, according to which these birds opened their chests to feed their hungry chicks. This representation is also an allegory of Christ.
Seabirds in danger
It is known that there are about three hundred species of seabirds, among which there are one hundred and ten species that are seriously threatened, which constitutes about sixty million individuals, which means that they have suffered a decrease of 70% since 1950.
The threats that produce the greatest effects are those that manage to alter their habitat, such as pollution, climate change and commercial fishing. According to scientific information there are nine orders of seabirds which are:
- fetontiformes, which have three species known as rabijuncos;
- pelecaniformes, which are divided into three species of pelicans, and are not threatened or at risk;
- podicipediformes, with four species of grebes and grebes, among which is an endangered species, the red-necked grebe;
- gaviformes, with five species of loons, divers, without threats or risks to their existence;
- sphenisciformes, which are divided into eighteen species of penguins, with ten species threatened and at risk;
- anseriformes, divided into one hundred and eighty species in three families, but only twenty-one species of seabirds, including ducks, serretas and eiders, of which four are threatened and at risk;
- suliformes, with forty-five species of seabirds, including frigatebirds and cormorants, of which fifteen are threatened and at risk;
- caradriiformes, which have XNUMX species, including gulls, terns and puffins, of which XNUMX are threatened and at risk; and
- procellariiforms, which have one hundred and forty species, including albatrosses, shearwaters, petrels, of which sixty-four are threatened).
Seabirds and plastic
The consequences of the appearance of plastic in the seas on turtles, whales and dolphins are well known by specialists and non-specialists, and there is documentation that proves it. However, what is not yet well documented is the effect that plastic has caused on seabirds and that is beginning to cause more concern today, because it has been shown that dumping waste into the sea is an activity that has not stopped.
The effect produced by plastics is becoming increasingly known in a better way. 80 of the 135 species of birds that have been studied between the years 1962 and 2012 have ingested plastic.
Furthermore, on average, 29% of the birds, taken into account individually, had plastic residues in their intestines during the analyzed period. These are the results of a compilation of research published in the journal PNAS (Proceedings of the National Academy of Sciences of the United States of America) in 2015 and carried out by scientists from the University of California.
It is believed that if these same analyzes were carried out today, the percentage of plastic ingestion would reach 90% of the birds. In fact, it has been said that the ingestion of plastic is increasing in seabirds and will be observable in 99% of the species in the year 2050, therefore, the only solution to prevent this from happening is to implement measures that help manage waste effectively.
toxins in the body
The most serious repercussion in the consumption of plastic waste that, due to its accumulation in the stomach, can end up obstructing the digestive tract, and even cause the death of the bird due to starvation or suffocation. Another effect is that plastics can degrade in the stomach and contribute toxins to the body, an aspect that affects the health and physiology of birds. And finally, entanglement and snags occur with nets, hooks and other parts of fishing gear or even with floating debris that comes from the mainland.
The amount of plastic consumed by seabirds has been dramatically recorded by Laysan albatrosses (Phoebastria immutabilis), an endogenous species to Hawaii. Through this area of the Pacific Ocean runs one of the places where there are turns of ocean currents, concentrating a large amount of waste. It might be thought that adult albatrosses would ignore litter, and if they did, they have the ability to expel waste through their mouths.
The problem occurs when they are feeding the chicks, who collect all the plastic waste that the parents bring them. The effects are visible, after the end of the mating and breeding season, when all the birds migrate and leave behind, in the colony, the exposed corpses in which the mortality produced by the accumulation of plastic consumed by the offspring can be seen. . These types of images can be found on the internet and a thorough study is not required to determine the causes.
What factors explain this ingestion?
There are several seabirds that have an unusual sense of smell, and are guided by it to find food. They often use dimethyl sulfate as a guide compound, which is a chemical that emanates from plankton. The bad news is that this same substance is also released by the decomposing plastic, which causes the birds to become confused and consume it.
This discovery was released in the journal Science Advances, by scientists from the University of California. Consequently, the birds identify that smell with marine areas of plankton, which are naturally highly productive, ideal for finding their prey, but it does not come from an area where they can find them, and they let themselves be guided by the smell to find their prey. food, being a mixture of their olfactory guide with their visual guide what leads the birds to consume the plastic.
The ingestion of plastic elements produces negative effects, particularly in the group of procellariiformes, pelagic birds, which obtain their food by fishing far from the coast, in the center of the ocean, as is the case of petrels, albatrosses, shearwaters and the fulmars.
In the Mediterranean Sea, this issue particularly affects the three species of shearwaters that live there, the Mediterranean, the Coryx and the Balearic, and the European storm-petrel, birds that usually move across the high seas and are strange to see from the coast , even if they approach their colonies, since they only visit their nests at night.
Gulls or cormorants are not likely to die from ingesting plastic, as they are capable of regurgitating food debris that they cannot digest, and expelling it through their mouths. But many species of birds, like shearwaters, don't have that ability. Anything that enters your body either stays in it or is excreted through the cloaca.
It has been determined that in the case of shearwaters, there is a high degree of plastic intake, although in general they are small fragments. But the most harmful contamination is that of microplastics, whose presence has been observed in almost all the birds that are observed. In this case, the issue is not that the plastic causes obstructions in the bird's body, but that it becomes poisoned, due to the toxins that the plastic generates and that pass into the body when it degrades.
It is common to find birds that have become entangled in fishing gear or debris. A study in this regard concluded that gannets are relatively frequently entangled with plastics, especially nets. It is thought that the reason is that they confuse certain nets with their prey, especially when they are very brightly colored, such as red or blue. These birds can see underwater, so they see something with a color that catches their attention, they go for it and get stuck.
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