Ganso Común/Greylag Goose/Anser anser

Anatidae

El ánsar común, ganso común u oca común es una especie de ave anseriforme de la familia Anatidae autóctona de Eurasia y el norte de África. Esta especie es el ancestro silvestre de las ocas domésticas de Europa. Los gansos domésticos se han asilvestrado y extendido en otras partes del mundo, como en Australia.

Descripción

El ánsar común es el más grande y robusto de los gansos del género Anser. Se caracteriza por su cuerpo voluminoso, su largo cuello y su pico grueso y de color naranja o rosado, mientras que sus patas son rosadas.​ Mide entre 74 y 91 cm de largo, con una longitud de alas de entre 41,2 y 48 cm, lo que le confiere una envergadura alar de entre 147 y 180 cm.​ Su cola mide entre 6,2 y 6,9 cm, su pico mide entre 6,4 y 6,9 cm de largo, y su tarsos entre 7,1 y 9,3 cm. Suele pesar entre 2,16 y 4,56 kg, con una media alrededor de 3,3 kg. Los machos suelen ser más grandes que las hembras, siendo el dimorfismo sexual más pronunciado en la subespecie oriental rubirostris, que además es más grande de media que la subespecie nominal.

Su plumaje es gris parduzco, con las alas, la cabeza y cuello más oscuros, y el pecho y vientre más claros, con motas negras variables, siendo su parte caudal inferior blanquecina. Su cuello está ligeramente rayado longitudinalmente. Las plumas de su dorso y flancos tienen el borde blanquecino y tiene una línea blanca en el flanco superior. Sus coberteras están ligeramente coloreadas en contraste con las plumas de vuelo negruzcas.

Muchos gansos recién nacidos están cubiertos por plumón de color pardo oliváceo en la parte superior y amarillento oscuro en la inferior, y posteriormente cambia a un plumón gris parduzco más uniforme. Su pico inicialmente es gris negruzco y se va volviendo amarillento. Sus patas son de color gris oliváceo. Los juveniles son algo más parduzcos, aunque se diferencian principalmente de los adultos por la falta de motas negras en el vientre.​ Los gansos comunes pueden llegar a vivir diecisiete años.

Su voz es muy fuerte, a modo de trompeteo de tipo hoooonk, igual que la de las ocas domésticas.

Distribución y hábitat

Es un ganso de distribución paleártica e indomalaya. Habita en casi toda Europa y gran parte de Asia, en zonas costeras y humedales. Cría principalmente en el norte y este de Europa, extendiéndose su zona de cría por una franja que va desde Islandia, las islas Británicas y las costas de Escandinavia y llega hasta el norte de China y la mitad sur del Krai de Jabárovsk, en el sureste de Rusia, pasando por Asia Central y Mongolia. En invierno migra al sur de Europa, oriente medio y el norte de la región indomalaya, además del extremo noroccidental de África (el norte de Marruecos, Túnez y Argelia). La mayor parte de los gansos de Europa pasan el invierno en las marismas del Guadalquivir, las lagunas de Villafáfila,​ el lago Ischkeul de Túnez y en el oeste de Argelia.

Los gansos domésticos se asilvestran con facilidad y han producido poblaciones estables en Australia.

Taxonomía

La primera descripción científica de esta especie fue realizada por Carlos Linneo en su obra Systema naturae en 1758 con el mismo nombre que en la actualidad, Anser anser.​ Se reconocen tres subespecies:

• Anser anser anser – cría en el noroeste de Eurasia y pasa el invierno en el norte de África, España y resto de la Europa mediterránea e Irán;
• Anser anser rubrirostris – cría en el noreste de Eurasia y pasa el inverno en el sur de Asia;
• Anser anser domesticus – todas las variedades de ocas domésticas procedentes de Eurasia.

Comportamiento

Los gansos comunes pueden ser tanto diurnos como nocturnos. Si son perturbados con frecuencia accederán a sus zonas de alimentación solo por la noche. Los gansos comunes son aves migratorias que se desplazan hacia el sur o el suroeste en invierno, aunque existen poblaciones sedentarias en zonas costeras o menos frías que son sedentarias, como las que crían en el noroeste de Europa. Esta especie es uno de las últimos gansos en emprender la migración invernal.​ Es característica de su migración la formación en V, que reduce la resistencia del aire, en la que los individuos se turnan en la posición de cabeza que es en la que más cuesta avanzar. Sus rutas migratorias no están marcadas genéticamente sino que los individuos de cada población tienen que aprenderlas siguiendo a los veteranos. Fuera de la época de cría los gansos forman grandes bandadas que permanecen juntas en los humedales y zonas de alimentación.

Alimentación

Se alimenta pastando hierbas y brotes del suelo; a veces escarba buscando raíces y bulbos. También recolectan plantas flotantes, pero raramente sumergen su cabeza en el agua.​ En otoño suelen rebuscar entre los rastrojos de los campos de maíz y a finales de verano en los de cereales en busca de los energéticos granos.​ Por razones de seguridad prefieren pastar en lugares despejados, por eso los pastizales dedicados al ganado y los campos de labor son ideales para ellos.

Reproducción

Los ánsares comunes por lo general se emparejan de por vida, pero si pierden a su pareja lo reemplazarán por otro. Dependiendo de la ubicación la época de cría empieza entre mediados de marzo y finales de abril. El lugar de nidificación preferido de los gansos grises son los lagos con amplias extensiones de cañaverales alrededor y prados adyacentes, que utilizan para alimentarse, aunque también pueden desplazarse lejos para pastar. Los ánsares comunes también pueden criar en los pantanos, marismas, en las islas fluviales boscosas, ríos de corriente lenta y llanuras de inundación. Suelen reproducirse en colonias poco densas con gran distancia entre nidos.

Anida en el suelo, en un hueco que tapiza parcialmente. Solo en las zonas muy húmedas los nidos se ubican sobre grandes acumulaciones de plantas palustres. Pone de cuatro a seis huevos en una sola nidada por año, siendo las puestas desde finales de marzo a principios de junio. Sus huevos son blancos y de forma casi elíptica. Por lo general cada huevo es puesto a intervalos de poco más de veinticuatro horas. La incubación la realiza solo la hembra, mientras que el macho se queda cerca del nido. La eclosión se produce tras unos veintisiete a veintinueve días, y los polluelos tardan en desarrollarse entre cincuenta y sesenta días. Generalmente los juveniles se quedan junto a sus padres hasta la siguiente época de cría y hacen juntos la migración.

Gansos domésticos

Existen numerosas razas domésticas europeas que se crían como aves de corral, aunque todas se consideran pertenecientes a la subespecie Anser anser domesticus. Son criadas especialmente por su carne y para elaborar foie gras, aunque también se consumen sus huevos. También son usadas como aves ornamentales en estanques de parques y jardines. Entre las variedades domésticas destacan:

• el ganso de Toulouse o ganso de Tolosa – ave procedente de la cría selectiva del ganso común salvaje en Toulouse, Francia.
• la oca del Ampurdán – ave procedente de la cría selectiva del ganso común salvaje en el norte de Cataluña. Se caracteriza por ser blanca y poseer un característico copete sobre la cabeza.

Estas aves son reconocidas por su agresividad territorial en las granjas tanto con otras aves como con los humanos, y por eso las ocas han sido usadas tradicionalmente como animales guardianes en las granjas, que logran ser incluso más eficientes que un perro guardián alertando a sus dueños de la presencia de un intruso, debido a que están siempre alerta y organizan un gran alboroto de gritos y graznidos en cuanto detectan a un extraño.

Estos gansos domésticos también son aprovechados para consumo humano, principalmente sus huevos, su carne y su hígado con el cual se fabrica el preciado paté foie gras.

Conservación

Desde sus tasas de población más bajas en la década de 1970, cuando la población silvestre total europea era de unos 20.000 ejemplares, la tendencia de su población ha sido aumentar, con aproximadamente 170.000 ejemplares en los años 1980, hasta unos 250.000 gansos en 2003. Esto ha supuesto no solo que sus zonas tradicionales de reproducción hayan aumentado su densidad, sino que también se han expandido a zonas donde habían desaparecido, especialmente en Alemania y los Países Bajos.

Greylag goose

The greylag goose (Anser anser) is a species of large goose in the waterfowl family Anatidae and the type species of the genus Anser. It has mottled and barred grey and white plumage and an orange beak and pink legs. A large bird, it measures between 74 and 91 centimetres (29 and 36 in) in length, with an average weight of 3.3 kilograms (7.3 lb). Its distribution is widespread, with birds from the north of its range in Europe and Asia migrating southwards to spend the winter in warmer places. It is the type species of the genus Anser and is the ancestor of the domestic goose, having been domesticated at least as early as 1360 BC. The genus name is from anser, the Latin for «goose».

Greylag geese travel to their northerly breeding grounds in spring, nesting on moorlands, in marshes, around lakes and on coastal islands. They normally mate for life and nest on the ground among vegetation. A clutch of three to five eggs is laid; the female incubates the eggs and both parents defend and rear the young. The birds stay together as a family group, migrating southwards in autumn as part of a flock, and separating the following year. During the winter they occupy semi-aquatic habitats, estuaries, marshes and flooded fields, feeding on grass and often consuming agricultural crops. Some populations, such as those in Southern England and in urban areas across the species’ range, are primarily resident and occupy the same area year-round.

Taxonomy

Anser anser, the greylag goose, is a member of the waterfowl family Anatidae. It was first described by the Swedish naturalist Carl Linnaeus in 1758 as Anas anser, but was transferred two years later to the new genus Anser, erected by the French zoologist Mathurin Jacques Brisson, where it is the type species. Two subspecies are recognised; A. a. anser, the western greylag goose, breeds in Iceland and north and central Europe; A. a. rubrirostris, the eastern greylag goose, breeds in Romania, Turkey and Russia eastwards to northeastern China. The two subspecies intergrade where their ranges meet. The greylag goose sometimes hybridises with other species of goose including the barnacle goose (Branta leucopsis) and the Canada goose (Branta canadensis), and occasionally with the mute swan (Cygnus olor).^[3] The greylag goose was one of the first animals to be domesticated; this happened at least 3000 years ago in Ancient Egypt, the domestic breed being known as A. a. domesticus. As the domestic goose is a subspecies of the greylag goose they are able to interbreed, with the offspring sharing characteristics of both the wild and tame birds.

Description

The greylag is the largest and bulkiest of the grey geese of the genus Anser, but is more lightly built and agile than its domestic relative. It has a rotund, bulky body, a thick and long neck, and a large head and bill. It has pink legs and feet, and an orange or pink bill with a white or brown nail (hard horny material at tip of upper mandible). It is 74 to 91 centimetres (29 to 36 in) long with a wing length of 41.2 to 48 centimetres (16.2 to 18.9 in). It has a tail 6.2 to 6.9 centimetres (2.4 to 2.7 in), a bill of 6.4 to 6.9 centimetres (2.5 to 2.7 in) long, and a tarsus of 7.1 to 9.3 centimetres (2.8 to 3.7 in). It weighs 2.16 to 4.56 kilograms (4.8 to 10.1 lb), with a mean weight of around 3.3 kilograms (7.3 lb). The wingspan is 147 to 180 centimetres (58 to 71 in). Males are generally larger than females, with the sexual dimorphism more pronounced in the eastern subspecies rubirostris, which is larger than the nominate subspecies on average. Three domesticated hybrids of greylag geese at Koutavos Lagoon, Cephalonia, Greece.Three eastern greylag geese (A. a. rubrirostris) at Keoladeo National Park in Rajasthan, India

The plumage of the greylag goose is greyish brown, with a darker head and paler breast and belly with a variable amount of black spotting. It has a pale grey forewing and rump which are noticeable when the bird is in flight or stretches its wings on the ground. It has a white line bordering its upper flanks, and its wing coverts are light coloured, contrasting with its darker flight feathers. Its plumage is patterned by the pale fringes of the feathers. Juveniles differ mostly in their lack of black speckling on the breast and belly and by their greyish legs. Adults have a distinctive ‘concertina’ pattern of folds in the feathers on their necks.

The greylag goose has a loud cackling call similar to that of the domestic goose, «aahng-ung-ung», uttered on the ground or in flight. There are various subtle variations used under different circumstances, and individual geese seem to be able to identify other known geese by their voices. The sound made by a flock of geese resembles the baying of hounds. Goslings chirp or whistle lightly, and adults hiss if threatened or angered.

Distribution and habitat

This species has a Palearctic distribution. The nominate subspecies breeds in Iceland, Norway, Sweden, Finland, the Baltic States, northern Russia, Poland, eastern Hungary and Romania. It also breeds locally in the United Kingdom, Denmark, Germany, Austria, the Czech Republic, Slovakia and North Macedonia. The eastern race extends eastwards across a broad swathe of Asia to China. European birds migrate southwards to the Mediterranean region and North Africa. Asian birds migrate to Azerbaijan, Iran, Pakistan, northern India, Bangladesh and eastward to China. In North America, there are both feral domestic geese, which are similar to greylags, and occasional vagrant greylags. Greylag geese seen in the wild in New Zealand probably originated from the escape of farmyard geese, and a similar situation has occurred in Australia, where feral birds are now established in the east and southeast of the country.

In their breeding quarters, they are found on moors with scattered lochs, in marshes, fens and peat-bogs, besides lakes and on little islands some way out to sea. They like dense ground cover of reeds, rushes, heather, bushes and willow thickets. In their winter quarters, they frequent salt marshes, estuaries, freshwater marshes, steppes, flooded fields, bogs and pasture near lakes, rivers and streams. They also visit agricultural land where they feed on winter cereals, rice, beans or other crops, moving at night to shoals and sand-banks on the coast, mud-banks in estuaries or secluded lakes. Large numbers of immature birds congregate each year to moult on the Rone Islands near Gotland in the Baltic Sea.

Since the 1950s, increases in winter temperatures have resulted in greylag geese, breeding in central Europe, reducing their winter migration distances. Wintering grounds closer to home can therefore be exploited, meaning that the geese can return to set up breeding territories earlier the following spring.

In Great Britain, their numbers had declined as a breeding bird, retreating north to breed wild only in the Outer Hebrides and the northern mainland of Scotland. However, during the 20th century, feral populations have been established elsewhere, and they have now re-colonised much of England. These populations are increasingly coming into contact and merging.

The greylag goose has become an invasive species in several areas. In Norway, the number of greylag geese is estimated to have increased three- to fivefold between 1995 and 2015. As a consequence, farmers’ problems caused by goose grazing on farmland has increased considerably. This problem is also evident for the pink-footed goose. In the Orkney islands the population has increased dramatically: there were 300 breeding pairs, increasing to 10,000 in 2009, and 64,000 in 2019. Due to extensive damage caused to crops, the hunting season for the greylag goose in the Orkney islands is now most of the year.

Behaviour

In a group, many pairs of eyes are on watch.

Greylag geese are largely herbivorous and feed chiefly on grasses. Short, actively growing grass is more nutritious and greylag geese are often found grazing in pastures with sheep or cows. Because of its low nutrient status, they need to feed for much of their time; the herbage passes rapidly through the gut and is voided frequently. The tubers of sea clubrush (Bolboschoenus maritimus) are also taken as well as berries and water plants such as duckweed (Lemna) and floating sweetgrass (Glyceria fluitans). In wintertime they eat grass and leaves but also glean grain on cereal stubbles and sometimes feed on growing crops, especially during the night. They have been known to feed on oats, wheat, barley, buckwheat, lentils, peas and root crops. Acorns are sometimes consumed, and on the coast, seagrass (Zostera sp.) may be eaten. In the 1920s in Britain, the pink-footed goose «discovered» that potatoes were edible and started feeding on waste potatoes. The greylag followed suit in the 1940s and now regularly searches for tubers on ploughed fields. They also consume small fish, amphibians, crustaceans, molluscs and insects. Six eggs in the nest at Mekszikópuszta, HungaryA group of gosling of greylag goose

Greylag geese tend to pair bond in long-term monogamous relationships. Most such pairs are probably life-long partnerships, though 5 to 8% of the pairs divorce and re-mate. Birds in heterosexual pairs may engage in promiscuous behavior, despite the opposition of their mates.

Homosexual pairs are common (14 to 20% of the pairs may be ganders, depending on flock), and share the characteristics of heterosexual pairs with the exceptions that the bonds appear to be closer, based on the intensity of their displays. Same-sex pairs also engage in courtship and sexual relations, and often assume high-ranking positions in the flock as a result of their superior strength and courage, leading some to speculate that they may serve as guardians of the flock. The orientations of the birds are generally flexible, as more than half of widowers re-pair with a bird of the opposite sex.

The nest is on the ground among heather, rushes, dwarf shrubs or reeds, or on a raft of floating vegetation. It is built from pieces of reed, sprigs of heather, grasses and moss, mixed with small feathers and down. A typical clutch is four to six eggs, but fewer eggs or larger numbers are not unusual. The eggs are creamy-white at first but soon become stained, and average 85 by 58 millimetres (3.3 by 2.3 in). They are mostly laid on successive days and incubation starts after the last one is laid. The female does the incubation, which lasts about twenty-eight days, while the male remains on guard somewhere near. The chicks are precocial and able to leave the nest soon after hatching. Both parents are involved in their care and they soon learn to peck at food and become fully-fledged at eight or nine weeks,^[11] about the same time as their parents regain their ability to fly after moulting their main wing and tail feathers a month earlier. Immature birds undergo a similar moult, and move to traditional, safe locations before doing so because of their vulnerability while flightless. A migrating flock

Greylag geese are gregarious birds and form flocks. This has the advantage for the birds that the vigilance of some individuals in the group allows the rest to feed without having to constantly be alert to the approach of predators. After the eggs hatch, some grouping of families occur, enabling the geese to defend their young by their joint actions, such as mobbing or attacking predators. After driving off a predator, a gander will return to its mate and give a «triumph call», a resonant honk followed by a low-pitched cackle, uttered with neck extended forward parallel with the ground. The mate and even unfledged young reciprocate in kind.

Young greylags stay with their parents as a family group, migrating with them in a larger flock, and only dispersing when the adults drive them away from their newly established breeding territory the following year. At least in Europe, patterns of migration are well understood and follow traditional routes with known staging sites and wintering sites. The young learn these locations from their parents which normally stay together for life. Greylags leave their northern breeding areas relatively late in the autumn, for example completing their departure from Iceland by November, and start their return migration as early as January. Birds that breed in Iceland overwinter in the British Isles; those from Central Europe overwinter as far south as Spain and North Africa; others migrate down to the Balkans, Turkey and Iraq for the winter.

In human culture

Ancient Egyptianstele showing Amun-Ra as goose, man, and ram. 25th dynasty, c. 700 BC.

The greylag was once revered across Eurasia. It was linked with the goddess of healing, Gula, a forerunner of the Sumerian fertility goddess Ishtar, in the cities of the Tigris-Euphrates delta over 5,000 years ago. In Ancient Egypt, geese symbolised the sun god Ra. In Ancient Greece and Rome, they were associated with the goddess of love, Aphrodite, and goose fat was used as an aphrodisiac. Since they were sacred birds, they were kept on Rome’s Capitoline Hill, from where they raised the alarm when the Gauls attacked in 390 BC. Wood engraving «The Tame Goose, Anas anser» by Thomas Bewick, A History of British Birds, 1804

The goose’s role in fertility survives in modern British tradition in the nursery rhyme Goosey Goosey Gander, which preserves its sexual overtones («And in my lady’s chamber»), while «to goose» still has a sexual meaning. The tradition of pulling a wishbone derives from the tradition of eating a roast goose at Michaelmas, where the goose bone was once believed to have the powers of an oracle. For that festival, in Thomas Bewick’s time, geese were driven in thousand-strong flocks on foot from farms all over the East of England to London’s Cheapside market, covering some 8 or 9 miles (13 or 14 km) per day. Some farmers painted the geese’s feet with tar and sand to protect them from road wear as they walked. Greylag geese were domesticated by at least 1360 BC, when images of domesticated birds resembling the eastern race, Anser anser rubirostris (which like modern farmyard geese, but unlike western greylags, have a pink beak) were painted in Ancient Egypt. Goose feathers were used as quill pens, the best being the primary feathers of the left wing, whose «curvature bent away from the eyes of right-handed writers». The feathers also served to fletch arrows. In ethology, the greylag goose was the subject of Konrad Lorenz’s pioneering studies of imprinting behaviour.

Fuentes: Wikipedia/eBird/xeno-canto