Phalacrocorax carbo
Phalacrocorax carbo
The great cormorant (Phalacrocorax carbo (Linnaeus, 1758)) is an aquatic bird belonging to the Phalacrocoracidae family.
Systematics –
From the systematic point of view it belongs to the Eukaryota Domain, Animalia Kingdom, Phylum Chordata, Aves Class, Suliformes Order, Phalacrocoracidae Family and therefore to the Phalacrocorax Genus and to the P. carbo Species.
Geographical Distribution and Habitat –
The great cormorant is a widespread bird throughout Eurasia and Australasia, as well as in the north-eastern regions of North America and in the northern parts of Africa. It is a species mostly linked to the waters that are both salty and fresh.
The species breeds in the extreme North-East of the United States, in Terranova and in Greenland; in Europe, from northern Norway to the Mediterranean basin. On the African continent, inhabits the Mediterranean and Atlantic coasts as far as Mauritania and is widespread in southern Africa. In Asia, it is present as far as India and China; in Japan, only the island of Honshu hosts its own subspecies. Elsewhere, it is found in East Africa and Southeast Asia. Another subspecies lives in Australia, Tasmania, New Zealand and the Chatham Islands.
It is therefore a “cosmopolitan” species, which inhabits practically all continents. The nominal subspecies (Phalacrocorax carbo carbo) inhabits the northern Atlantic coasts; the subspecies Phalacrocorax carbo sintesis is found in central and southern Europe and in Asia. In Italy, the Cormorant is a regular, migratory, locally extending and stationary nesting winter visitor.
These birds, which prefer the sheltered seas, avoid the deep waters even close to the land and rarely move away from the shores: they can be seen on the lakes, the basins, the deltas, the estuaries, the great watercourses, generally when the current is weak, more rarely if it is torrents.
In Italy the species always nests in proximity to the water: the largest site of presence is that of Valle Santa (Regional Park of the Po Delta).
Description –
Phalacrocorax carbo is a bird that has a long and tapering black body. It has a robust beak with a characteristic hook shape and by means of a long and elastic “S” shaped neck it is able to feed on fish, absorbing them directly into the esophagus.
It is a species that often reaches large dimensions: the length can vary from 79 to 102 cm and the wingspan from 121 to 160 cm. The weight ranges from 1.5 to 5.3 kg. The Cormorant has permeable feathers and spends a lot of time in the sun drying out.
The feathers of the wings are bronze colored, bordered in black and create a chromatic contrast with the rest of the body; the lower plumage is almost entirely black. The adult males and females are distinguished from the young, which, in the first year of life, have a belly covered with white feathers that form a large or more extensive patch. During the second year, this white band disappears, but they still remain recognizable by the brownish color of the plumage, which begins to resemble that of adults only during the third year of life.
The moult of adults takes place twice a year: from July (after the breeding season) to December for tail feathers and, before nesting, from January to April for feathers of the head, neck and body.
The legs, with large membranes, allow a powerful push under water, where the species can fish up to a depth of 6 meters.
Biology –
The biological cycle of Phalacrocorax carbo sometimes starts in the heart of winter. In this period the first rituals of the nuptial parade often take place, even if it is only at the end of February, but above all in March and April, that the sexual activity is more intense (the chicks will be born between April and July).
The most evident manifestation of this event is given by the nuptial livery: the plumage thus acquires brilliant shades with greenish reflections, purple or bronze, depending on the exposure to the sun’s rays, with showy white spots on the thighs; the nuptial livery of the continental cormorants is enriched, in the same period, with whitish feathers on the head and neck. The wedding dress is ephemeral: along the Breton coasts, for example, it is “worn” for a maximum of one month a year, as noted by the French ornithologist Marion.
The females are attracted by the calls of the male and approaches the chosen one, who then folds his head back several times and emits hoarse cries keeping the beak half-open and the wings slightly dangling. The female imitates him. During mating, the male holds the female’s neck and beak in its beak. Then the birds make each other toilets. During the mating season, the wedding parades and mating follow one another and can last until the beginning of the incubation of the eggs.
The maritime populations build the nest with algae mixed with various types of debris, on rocky islets or in cliff cliffs.
Those that nest in the hinterland instead set up a nest made of twigs, on the trees and sometimes in the reeds, at a distance of 2 or 3 meters (but also 10 meters) from the ground, near the rivers or bodies of water in which they feed themselves.
These materials are however always collected and transported by the male, while the female takes charge of the actual construction; it perfects its work even after the first eggs have been laid and works there for the entire breeding period of the young. The same nest is reused every year, sometimes becoming so large that it can reach one meter both in height and in the base diameter; the inner cup can be 30-40 centimeters wide. There are frequent fights between birds when the colony is very populated and the nests are attached to each other.
The first broods occur around mid-April and the last at the beginning of June. Each female lays 3 or 4 eggs (rarely 5 or 6), which are pale blue or greenish in color, long and oval (63 mm long and 40 mm wide at the most); these weigh an average of 55 grams and are placed, one after the other, at 2-3 day intervals.
The incubation of the eggs lasts from 28 to 31 days and begins with the laying of the first egg: the hatches are thus staggered over time and the last born of a brood can break the shell ten days after the others. The eggs are hatched both by the female and by the male who alternate also in search of food.
Incubation shifts have a variable duration depending on the natural environment and the individual species. When one of the partners returns to the nest to replace the hatching, he often carries out a sort of greeting to be recognized and to strengthen the bonds of the couple. If the companion does not want to abandon the brood, it may happen that the newly arrived bird tries to push it gently out of the nest. When an egg hatches, the shell is removed from the nest by one of the two adults. A new deposition can take place, in July or August, if the eggs of the first brood have been destroyed.
At birth, the chicks are balls of whitish down with a disproportionate neck.
The father and mother take turns to feed each chick on average twice a day. When the adult reaches the platform of the nest, it approaches the little that wants to feed and opens the beak: the chick then completely shoves its head in the goiter to take food, a whitish mixture of predigested fish meat.
The first flight of the small cormorants occurs at around 50 days, but returns regularly to the nest to be fed for over a month. After this period, the young cormorants become independent. The plumage at this point has taken on a dark brown color, while the belly is whitish: it will remain so in the first 3 years of life. Sexual maturity is reached only around 4-5 years, very rarely around 3 years. This does not prevent the young man from trying to mate even before he has reached the appropriate age, but his attempts are destined for failure.
Once they reach independence, the young cormorants begin to wander, starting in June and July, until the migration to the South begins at the arrival of autumn. The cormorants are erratic until they reach sexual maturity and, in summer, move along the coasts or in the humid areas of the interior, sometimes very far from the place where they were born.
Ecological Role –
The great cormorant is a bird that usually moves in flocks of a few units up to hundreds of individuals. It is a gregarious and nesting species from the third to fifth year of life in colonies. Daytime dormitories and roosts are located in wetlands scarcely frequented by humans.
These are extremely social birds. They live together in colonies that, during the reproduction period, include several hundred pairs. During the winter then the tendency to cohabitation is further accentuated and the birds are grouped in thousands along the rivers or on the large expanses of water obtaining several advantages: greater profitability in fishing, reinforcement of the cohesion of the groups and solicitation of nuptial behaviors. At night the cormorants gather in hundreds or thousands of resting places, dormitories, consisting of large trees that line the rivers, forming “clusters” of birds that settle there from sunset until late at night.
The cormorants, taking advantage of the mighty wings, can make daily trips of several tens of kilometers to reach the feeding areas or places of rest and mating. During the journey, the flocks are arranged in a wedge-shaped formation that facilitates their flight: a bird stands at the head of the group so that the others can move forward in its wake with less effort. The role of “guide” is taken in turn and regularly by other specimens.
When the breeding season is over, almost the entire colony sets off for the South: making a long flight that goes from several hundred kilometers to 2000, in order to reach the suitable wintering areas.
The essential diet of Cormorano is represented by fish. However, this bird spends only 20% of their day fishing, preferably in the morning and early afternoon: the search for food usually ceases long before sunset.
Studies conducted in the marine environment have shown that this species, although it eats many varieties of fish, prefers cod, hake, eel, herring and sardines. In fresh water the cormorant eats especially perch, catfish, bream, roach, tench and trout. In artificial basins, where catfish abounds, this is the most sought after prey also because it is easy to catch.
The cormorant is a lazy animal: he does not like to spend too much time looking for food. It swallows between 400 and 700 grams of fish per day, about 15-17% of its weight, generally choosing the most abundant and easiest to catch in its feeding area. Sometimes it needs some time to swallow the fish, if it is large. It may also happen that a bird that is too voracious is suffocated by the enormous bite: several specimens have been found dead due to their great greed. The great voracity has caused serious trouble for the cormorant, who has often been accused of plundering fish breeding basins and then ruthlessly hunted by man.
Seagulls often fly near the common cormorant because they indirectly feed on the fruits of its fishing.
From an ecological point of view, the Nordic populations (Europe, North America, Greenland, Iceland) are the least sedentary and migrate, for winter, up to over the 40th parallel. In the twentieth century this distribution has undergone great changes, above all in the inner lands, due, on the one hand, to the persecution of which these birds have been victims by fishermen and, on the other, by the transformation of some habitats.
Guido Bissanti
Sources
– Wikipedia, the free encyclopedia.
– C. Battisti, D. Taffon, F. Giucca, 2008. Atlas of breeding birds, Gangemi Editore, Rome.
– L. Svensson, K. Mullarney, D. Zetterstrom, 1999. Guide to the birds of Europe, North Africa and the Near East, Harper Collins Publisher, United Kingdom.