Nombre en español: Pato Real

Nombre en ingles: Mallard

Nombre científico: Anas platyrhynchos

Familia: Anatidae

Foto: Francisco Piedrahita

Canto: Stanislas Wroza

El ánade real o azulón (Anas platyrhynchos)​ es una especie de ave anseriforme de la familia Anatidae. Es un patode superficie muy común y extendido por el hemisferio norte. Habita áreas de temperatura templada de Norteamérica, Europa, Asia y el norte de África. Como ave migratoria también frecuenta Centroamérica y el Caribe, y ha sido introducido en Australia y Nueva Zelanda. Probablemente es el más conocido de todos los patos, y los patos domésticos pertenecen a esta especie.

Taxonomía y evolución

El ánade fue una de las muchas aves descritas científicamente por Carlos Linneo en su obra Systema naturæ de 1758, y todavía lleva su nombre binomial original.

Los ánades reales hibridan con sus parientes más cercanos dentro del géneroAnas, como el ánade sombrío, y con algunas especies más alejadas como ánade rabudo, produciendo diversos híbridos que pueden ser totalmente fértiles. Este inusual fenómeno que se produce entre las especies de patos es debido a que el azulón y los demás patos del género Anas han evolucionado muy rápido y recientemente, a finales del Pleistoceno. Esta radiación de linajes se mantienen separados al no coincidir sus áreas de distribución o por motivos de comportamiento, pero todavía no son genéticamente incompatibles.​ Además los azulones son con específicos de los patos domésticos (Anas platyrhynchos domesticus) y completamente fértiles en su cruzamiento.

A juzgar por su biogeografía el azulón parece estar más próximo a sus parientes indopacíficos que a los americanos. Según las secuencias de su ADN mitocondrial de los bucles de desplazamiento,​ habrían evolucionado en una región de Siberia y alrededores. Además aparece repentinamente entre los restos fósiles de Europa sin tener un candidato claro para ser su ancestro en la zona. La paleoespecie de gran tamaño que formaban al menos las poblaciones europeas y del oeste de Asia durante el Pleistoceno se ha denominado Anas platyrhynchos palaeoboschas.

Existen diferencias en el ADN mitocondrial entre los ánades reales de Norteamérica y Eurasia,​ pero no se encuentra un patrón claro de diferenciación en su genoma nuclear. Aparecen haplotipos típicos de los parientes cercanos norteamericanos y del ánade picopinto en los azulones de los alrededores del mar de Bering. Hay una población de ánades reales en las islas Aleutianas que parece estar evolucionando hacia una subespecie, ya que su flujo genético con las demás poblaciones es muy reducido.

El tamaño de los ánades reales varía clinalmente, por lo que los individuos de Groenlandia son más grandes, robustos y con el pico más corto que las poblaciones del sur. Algunos ornitólogos separan a los azulones de Groenlandia en una subespecie (A. p. conboschas).

Descripción

El ánade real es un pato de tamaño medio, aunque ligeramente más pesado que la mayoría de los patos de superficie. Mide entre 50-65 cm de largo (de los cuales dos tercios corresponden al cuerpo), tiene una envergadura alar de 81-98 cm, y suele pesar entre 0,72-1,58 kg. Sus medidas corporales estándar son: cuerda máxima del ala entre 25,7 y 30,6 cm, pico entre 4,4 y 6,1 cm y tarso entre 4,1 y 4,8 cm.

Presenta un marcado dimorfismo sexual en su plumaje. El macho en plumaje reproductivo es inconfundible. Su cabeza y cuello son de color verde oscuro brillante enmarcados con una lista blanca a modo de collar. Su pecho es castaño con tonos púrpura. El resto de su plumaje es grisáceo (más oscuro en las partes superiores) salvo el obispillo y las plumas centrales de la cola, rizadas hacia arriba, que son negros, las plumas laterales de la cola, que son blancas, y el espejuelo de las alas. La hembra tiene un plumaje de colores más apagados, predominantemente veteado en tonos pardos, de marcado contraste entre tonos claros y oscuros debido a que cada pluma puede ser en parte desde el pardo oscuro al crema claro. Esta coloración es compartida por la mayoría de las hembras de patos de superficie. Su cabeza es principalmente de tonos crema con una lista ocular y píleo oscuros. Ambos sexos tienen un característico espejuelo en sus plumas secundarias de color azul iridiscente (o morado según el ángulo en que se vea) con un borde interior negro y otro exterior blanco. En el caso de la hembra, el espejuelo permite diferenciarla de las hembras de otras especies de patos. El pico del macho es amarillo con la punta negra, mientras que el de la hembra es más oscuro, oscilando del naranja manchado al pardo negruzco. Las patas de ambos son de color naranja. Tras la época de cría, los machos mudan su plumaje pasando al plumaje de eclipse, de tonos similares al de las hembras. Al final de esta muda estival, ambos sexos pierden las plumas de vuelo aproximadamente durante un mes (periodo de mancada), por lo que temporalmente carecen de su característico espejuelo.

Al nacer los patitos están cubiertos de plumón de color amarillo en las partes inferiores y el rostro, y pardo negruzco en las superiores, con algunas motas amarillas. Sus patas y pico son negruzcos. Con el primer emplumado los patitos adquieren un plumaje de tonos pardos similar al de las hembras, aunque más veteado, y sus patas y pico se van aclarando. El periodo de emplumado termina a los dos meses tras la eclosión. Los juveniles empiezan a volar a los tres o cuatro meses, cuando sus alas y musculatura están completamente desarrolladas. Los juveniles pueden distinguirse por el color de su pico, amarillo para los machos y naranja o pardo para las hembras; su pecho, que es pardo rojizo en el caso de los machos, y las plumas centrales de la cola, que están rizadas hacia arriba en los machos y son rectas en las hembras.

Al acercarse al periodo de madurez sexual (entre los 6-10 meses), el plumaje de las hembras permanece igual mientras que el de los machos va cambiando paulatinamente hasta alcanzar los tonos del adulto. Este cambio en el plumaje es similar al de los machos adultos al llegar la primavera y volver a adquirir el plumaje reproductivo. La madurez sexual de los azulones se produce a los 14 meses y tienen una esperanza de vida de tres años.

Los patos domésticos pueden ser de coloración similar a los patos silvestres, blancos y de otros colores no presentes en las poblaciones salvajes.

Son una especie ruidosa, los machos emiten un graznido nasal agudo a modo de bocinazo, mientras que las hembras producen el cuac más grave que en general se atribuye a los patos.

Distribución y hábitat

Los ánades reales están ampliamente distribuidos por el hemisferio norte y han sido introducidos en algunas regiones del hemisferio sur. Se encuentran de forma natural en Norteamérica desde Alaska y Groenlandia hasta México, las islas de Hawái, la mayor parte de Eurasia desde Islandia y Escandinavia por el oeste hasta Siberia, China y Japón por el este, además del norte de África. Ha sido introducido en Australia y Nueva Zelanda. Es un ave migratoria de larga distancia en las partes septentrionales de su área de distribución, pasando el invierno en las del sur. Por ejemplo, los de Norteamérica pasan el invierno en México, y también se adentran regularmente en América Central y el Caribe entre septiembre y mayo.

Los azulones habitan en una gran variedad de hábitats y climas, desde la tundra ártica a las regiones subtropicales. Se encuentra tanto en humedales de aguas dulces como salada, incluidos los lagos, las lagunas, los ríos, pantanos y estuarios, además de las ensenadas someras y el mar abierto cercano a la costa; y también los parques y zonas urbanas. Prefieren las aguas poco profundas, de menos de un metro, y suelen evitar las más profundas. Y se sienten atraídos por las masas de agua con vegetación acuática.

Comportamiento

Es un ave muy gregaria fuera de la época de cría, y puede formar grandes bandadas. Es un pato bastante arisco y desconfiado, que raramente permite el acercamiento a corta distancia, siendo normalmente el primero que huye ante la presencia humana (salvo los residentes en las urbes). Se agrupa para sestear durante el día y por la noche se desplaza a los comederos. Su gran capacidad de adaptación y aprovechamiento de distintas fuentes de alimentos son las razones de su numerosa población.

Alimentación

Generalmente se alimentan en la superficie del agua, llegando a sumergir medio cuerpo, o pastan cerca de las orillas. Los ánades reales son omnívoros y muy flexibles respecto a sus elecciones alimenticias. Su dieta puede variar según varios factores, como la época de su ciclo de reproducción, variaciones en la disponibilidad de alimentos y la competencia inter e intraespecífica.​ La mayor parte de la dieta del azulón se compone de gran variedad de semillas y otra materia vegetal, incluidas raíces y tubérculos, e invertebrados como gasterópodos, insectos (entre los que se encuentran los escarabajos, moscas, mariposas, libélulas y figáneas), crustáceos y gusanos, también se ha registrado que comen pequeñas ranas. Se ha registrado que durante la época de cría los machos consumen un 37,6 % materia animal y un 62,4 % de materia vegetal, especialmente Echinochloa crus-galli, y las hembras que no ponen huevos comen un 37,0 % de materia animal y un 63,0 % de materia vegetal. En cambio las hembras que van a poner huevos consumen un 71,9 % de materia animal y solo un 28,1 % materia vegetal.​ El resto del año la mayoría de la dieta de este pato está formada por plantas, especialmente durante la migración de otoño y el invierno.

Reproducción

Los ánades reales generalmente forman parejas (en octubre y noviembre en su área autóctona) solo hasta que las hembras ponen los huevos al principio de la primavera. En este periodo el macho la deja y se une a otros machos en espera de la época de muda estival que empieza en junio (en el hemisferio norte). Una vez adquiridas las plumas de contorno del plumaje de eclipse los machos pierden las plumas de vuelo quedando durante aproximadamente sin capacidad de vuelo, por lo que permanecen escondidos entre la vegetación acuática. Las hembras no sufrirán este proceso hasta haber terminado de criar a su nidada. En el periodo previo a la muda los machos todavía están sexualmente activos y algunos permanecen a la espera para engendrar puestas de reposición, con aquellas hembras que han perdido o abandonado la anterior) o para aparearse por la fuerza con cualquier hembra de pato que aparezca aislada, sin importar su especie o si está criando una prole de patitos.

El periodo de anidamiento puede ser muy estresante para las hembras ya que pueden poner más de la mitad de su peso en huevos. Para ello necesita mucho descanso y una zona de alimentación libre de depredadores. Cuando busca un lugar para anidar la hembra prefiere zonas ocultas, inaccesibles para los depredadores terrestres, o que tengan pocos depredadores en los alrededores. La puesta consta de entre 8-13 huevos, que son incubados durante 27-28 días hasta su eclosión. La hembra cuida a sus crías en solitario, que tardan 50-60 días en desarrollarse. Sus patitos son nidífugos y capaces de nadar y alimentarse solos desde el primer día. Los polluelos al nacer están recubiertos de plumón amarillo o marrón con la cara y otras manchas amarillas. La impronta les impulsa a seguir y quedarse junto a su madre, así no solo los protege y da calor sino que aprenden lo que necesitan sobre su hábitat y dónde y cómo alimentarse. Cuando los patitos se han convertido en juveniles capaces de volar, aprenden y recuerdan sus rutas migratorias tradicionales al permanecer junto a su madre hasta la siguiente época de cría.

Con frecuencia cuando se forman las parejas uno o varios machos quedan de lado. Estos grupos a veces persiguen a hembras de pato aisladas, incluso a las de otras especies, hasta que las cansan y entonces copulan con ella por turnos. Lebret (1961) y Cramp y Simmons (1977) denominaron a este comportamiento «vuelo de intento de violación». Los machos de azulón ocasionalmente persiguen a los machos de otras especies de patos, o incluso entre ellos, con la misma intención. En un caso se documentó «necrofilia homosexual», un macho copuló con otro macho al que había perseguido en vuelo y estaba muerto tras chocar con una ventana de vidrio.​ Esta investigación fue galardonada con el premio Ig Nobel de 2003.

Los ánades reales son en ocasiones objetivo de parásitos de puesta oportunistas como los porrones americanos, malvasías canelas, porrones bola, ánades frisos, ánades rabudos, patos cuchara, cercetas coloradas, porrones osculados y otros azulones. Estos huevos generalmente son aceptados cuando se parecen a sus propios, pero si no la hembra de azulón intenta expulsarlos o incluso abandona el nido si el parasitismo se produce durante la puesta.

Estado de conservación

A diferencia de otras aves acuáticas el ánade real se ha beneficiado de las alteraciones humanas del medio ambiente. Son muy adaptables y son capaces de vivir, e incluso prosperar, en medios humanizados y urbanos, que antes podían haber sustentado a otras especies de patos más sensibles. Su población y área de distribución son enormes, y aunque se cree que su población está disminuyendo ligeramente no se acerca ni de lejos a los umbrales de amenaza, por lo que la UICN lo considera una especie bajo preocupación menor.

La suelta de azulones en regiones donde no son nativos causa problemas debidos a la hibridación con los patos nativos, ya que se producen híbridos fértiles que contaminan genéticamente las poblaciones locales, y merman la posibilidad de supervivencia de los patos autóctonos más escasos. Los azulones son considerados una especie invasora en Nueva Zelanda y Sudáfrica. Allí, y en otros lugares, los ánades reales se están extendiendo con ayuda de la creciente expansión urbana e hibridan con sus parientes cercanos locales. Con el tiempo la hibridación ha creado un continuo de formas intermedias entre estas especies y el azulón, empezándose así a revertir el proceso de especiación. Esto ha causado preocupación por parientes del ánade real como el pato de Hawái, la subespecie A. s. superciliosa del ánade cejudo,​ el ánade sombrío, el ánade jaspeado, el ánade malgache,​ el ánade picolimón,​ el pato mexicano,​ en este último caso llegando incluso a cuestionarse si estas aves deberán considerarse una especie. En Florida se ha prohibido la posesión y cría de ánades reales para evitar así la hibridación con los patos jaspeados nativos. El ánade picopinto está sufriendo introgresión por parte de la población de azulones del Krai de Primorie, posiblemente debida a los cambios del hábitat debidos alcalentamiento global.

A su vez el acervo genérico los ánades reales silvestres, que son los ancestros de los patos domésticos, puede contaminarse por la hibridación de los patos domésticos y los patos asilvestrados.

Genoma

El genoma del ánade real fue secuenciado en 2013. Con su obtención, se observaron características importantes del mismo, como la contracción de familias de genes de la inmunidad con respecto a sus familias equivalentes en mamíferos. Además, dado que esta ave es un reservorio natural del virus de la gripe aviar, se identificaron genes cuyos patrones de expresión se alteran en respuesta a la infección de este virus, concretamente tras la infección con el subtipo H5N1.

Mallard

The mallard (/ˈmælɑːrd/ or /ˈmælərd/) (Anas platyrhynchos) is a dabbling duck that breeds throughout the temperate and subtropical Americas, Eurasia, and North Africa and has been introduced to New Zealand, Australia, Peru, Brazil, Uruguay, Argentina, Chile, Colombia, the Falkland Islands, and South Africa. This duck belongs to the subfamily Anatinae of the waterfowl family Anatidae. The male birds (drakes) have a glossy green head and are grey on wings and belly while the females (hens or ducks) have mainly brown-speckled plumage. Both sexes have an area of white-bordered black or iridescent blue feathers called a speculum on their wings; males especially tend to have blue speculum feathers. The mallard is 50–65 cm (20–26 in) long, of which the body makes up around two-thirds the length. The wingspan is 81–98 cm (32–39 in) and the bill is 4.4 to 6.1 cm (1.7 to 2.4 in) long. It is often slightly heavier than most other dabbling ducks, weighing 0.72–1.58 kg (1.6–3.5 lb). Mallards live in wetlands, eat water plants and small animals, and are social animals preferring to congregate in groups or flocks of varying sizes. This species is the main ancestor of most breeds of domesticated ducks.

The female lays eight to thirteen creamy white to greenish-buff spotless eggs, on alternate days. Incubation takes 27 to 28 days and fledging takes 50 to 60 days. The ducklings are precocial and fully capable of swimming as soon as they hatch.

The mallard is considered to be a species of least concern by the International Union for Conservation of Nature (IUCN). Unlike many waterfowl, mallards are considered an invasive species in some regions. It is a very adaptable species, being able to live and even thrive in urban areas which may have supported more localised, sensitive species of waterfowl before development. The non-migratory mallard interbreeds with indigenous wild ducks of closely related species through genetic pollution by producing fertile offspring. Complete hybridisation of various species of wild duck gene pools could result in the extinction of many indigenous waterfowl. The wild mallard is the ancestor of most domestic ducks, and its naturally evolved wild gene pool gets genetically polluted by the domesticated and feral mallard populations.

Taxonomy and evolution

The mallard was one of the many bird species originally described in the 1758 10th edition of Systema Naturae by Carl Linnaeus. He gave it two binomial names: Anas platyrhynchos and Anas boschas. The latter was generally preferred until 1906 when Einar Lönnberg established that A. platyrhynchos had priority as it appeared on an earlier page in the text. The scientific name comes from Latin Anas, «duck» and Ancient Greek πλατυρυγχος, platyrhynchus, «broad-billed» (from πλατύς, platys, «broad» and ρυγχός, rhunkhos, «bill»). The genome of Anas platyrhynchos was sequenced in 2013.

The name Mallard originally referred to any wild drake, and it is sometimes still used this way. It was derived from the Old French malart or mallart for «wild drake» although its true derivation is unclear. It may be related to, or at least influenced by, an Old High German masculine proper name Madelhart, clues lying in the alternate English forms «maudelard» or «mawdelard». Masle (male) has also been proposed as an influence.

Mallards frequently interbreed with their closest relatives in the genus Anas, such as the American black duck, and also with species more distantly related, such as the northern pintail, leading to various hybrids that may be fully fertile. This is quite unusual among such different species, and is apparently because the mallard evolved very rapidly and recently, during the Late Pleistocene. The distinct lineages of this radiation are usually kept separate due to non-overlapping ranges and behavioural cues, but have not yet reached the point where they are fully genetically incompatible. Mallards and their domesticated conspecifics are also fully interfertile.

Genetic analysis has shown that certain mallards appear to be closer to their Indo-Pacific relatives while others are related to their American relatives. Mitochondrial DNA data for the D-loop sequence suggests that mallards may have evolved in the general area of Siberia. Mallard bones rather abruptly appear in food remains of ancient humans and other deposits of fossilbones in Europe, without a good candidate for a local predecessor species. The large ice age palaeosubspecies that made up at least the European and west Asian populations during the Pleistocene has been named Anas platyrhynchos palaeoboschas.

Mallards are differentiated in their mitochondrial DNA between North American and Eurasian populations, but the nuclear genome displays a notable lack of genetic structure. Haplotypes typical of American mallard relatives and spotbills can be found in mallards around the Bering Sea. The Aleutian Islands hold a population of mallards that appear to be evolving towards a subspecies, as gene flow with other populations is very limited.

Also, the paucity of morphological differences between the Old World mallards and the New World mallard demonstrates the extent to which the genome is shared among them such that birds like the Chinese spot-billed duck are highly similar to the Old World mallard, and birds such as the Hawaiian duck are highly similar to the New World mallard.

The size of the mallard varies clinally; for example, birds from Greenland, though larger, have smaller bills, paler plumage, and stockier bodies than birds further south, and are sometimes classified as a separate subspecies, the Greenland mallard (A. p. conboschas).

Description

The mallard is a medium-sized waterfowl species that is often slightly heavier than most other dabbling ducks. It is 50–65 cm (20–26 in) long – of which the body makes up around two-thirds – has a wingspan of 81–98 cm (32–39 in), and weighs 0.72–1.58 kg (1.6–3.5 lb). Among standard measurements, the wing chord is 25.7 to 30.6 cm (10.1 to 12.0 in), the bill is 4.4 to 6.1 cm (1.7 to 2.4 in), and the tarsus is 4.1 to 4.8 cm (1.6 to 1.9 in).

The breeding male mallard is unmistakable, with a glossy bottle-green head and a white collar that demarcates the head from the purple-tinged brown breast, grey-brown wings, and a pale grey belly. The rear of the male is black, with white-bordered dark tail feathers. The bill of the male is a yellowish-orange tipped with black, with that of the female generally darker and ranging from black to mottled orange and brown. The female mallard is predominantly mottled, with each individual feather showing sharp contrast from buff to very dark brown, a coloration shared by most female dabbling ducks, and has buff cheeks, eyebrow, throat, and neck, with a darker crown and eye-stripe.

Both male and female mallards have distinct iridescent purple-blue speculum feathers edged with white, which are prominent in flight or at rest but temporarily shed during the annual summer moult. Upon hatching, the plumage of the duckling is yellow on the underside and face (with streaks by the eyes) and black on the back (with some yellow spots) all the way to the top and back of the head. Its legs and bill are also black. As it nears a month in age, the duckling’s plumage starts becoming drab, looking more like the female, though more streaked, and its legs lose their dark grey colouring. Two months after hatching, the fledgling period has ended, and the duckling is now a juvenile. Between three and four months of age, the juvenile can finally begin flying, as its wings are fully developed for flight (which can be confirmed by the sight of purple speculum feathers). Its bill soon loses its dark grey colouring, and its sex can finally be distinguished visually by three factors: 1) the bill is yellow in males, but black and orange in females; 2) the breast feathers are reddish-brown in males, but brown in females; and 3) in males, the centre tail feather (drake feather) is curled, but in females, the centre tail feather is straight. During the final period of maturity leading up to adulthood (6–10 months of age), the plumage of female juveniles remains the same while the plumage of male juveniles gradually changes to its characteristic colours. This change in plumage also applies to adult mallard males when they transition in and out of their non-breeding eclipse plumage at the beginning and the end of the summer moulting period. The adulthood age for mallards is fourteen months, and the average life expectancy is three years, but they can live to twenty.

Several species of duck have brown-plumaged females that can be confused with the female mallard. The female gadwall (A. strepera) has an orange-lined bill, white belly, black and white speculum that is seen as a white square on the wings in flight, and is a smaller bird. More similar to the female mallard in North America are the American black duck (A. rubripes), which is notably darker-hued in both sexes than the mallard, and the mottled duck (A. fulvigula), which is somewhat darker than the female mallard, and with slightly different bare-part colouration and no white edge on the speculum.

In captivity, domestic ducks come in wild-type plumages, white, and other colours. Most of these colour variants are also known in domestic mallards not bred as livestock, but kept as pets, aviary birds, etc., where they are rare but increasing in availability.

A noisy species, the female has the deep quack stereotypically associated with ducks. Male mallards make a sound phonetically similar to that of the female, a typical quack, but it is a deep and raspy and can also sound like breeeeze. When incubating a nest, or when offspring are present, females vocalise differently, making a call that sounds like a truncated version of the usual quack. They hiss if the nest or offspring are threatened or interfered with. When taking off, the wings of a mallard produce a characteristic faint whistling noise.

The mallard is a rare example of both Allen’s Rule and Bergmann’s Rule in birds. Bergmann’s Rule, which states that polar forms tend to be larger than related ones from warmer climates, has numerous examples in birds, as in case of the Greenland mallard which is larger than the mallards further south. Allen’s Rule says that appendages like ears tend to be smaller in polar forms to minimise heat loss, and larger in tropical and desert equivalents to facilitate heat diffusion, and that the polar taxa are stockier overall. Examples of this rule in birds are rare as they lack external ears, but the bill of ducks is supplied with a few blood vessels to prevent heat loss, and, as in the Greenland mallard, the bill is smaller than that of birds farther south, illustrating the rule.

Due to the variability of the mallard’s genetic code, which gives it its vast interbreeding capability, mutations in the genes that decide plumage colour are very common and have resulted in a wide variety of hybrids such as Brewer’s duck (mallard × gadwall, Anas strepera).

Distribution and habitat

The mallard is widely distributed across the Northern and Southern Hemispheres; in North America its range extends from southern and central Alaska to Mexico, the Hawaiian Islands, across Eurasia, from Iceland and southern Greenland and parts of Morocco (North Africa) in the west, Scandinavia and Britain to the north, and to Siberia, Japan, and South Korea, in the east, south-eastern and south-western Australia and New Zealand in the Southern hemisphere. It is strongly migratory in the northern parts of its breeding range, and winters farther south. For example, in North America, it winters south to the southern United States and northern Mexico, but also regularly strays into Central America and the Caribbean between September and May.

The mallard inhabits a wide range of habitats and climates, from Arctic tundra to subtropical regions. It is found in both fresh- and salt-water wetlands, including parks, small ponds, rivers, lakes and estuaries, as well as shallow inlets and open sea within sight of the coastline. Water depths of less than 0.9 metres (3.0 ft) are preferred, with birds avoiding areas more than a few metres deep. They are attracted to bodies of water with aquatic vegetation.

Behaviour

Feeding

The mallard is omnivorous and very flexible in its choice of food. Its diet may vary based on several factors, including the stage of the breeding cycle, short-term variations in available food, nutrient availability, and interspecific and intraspecific competition. The majority of the mallard’s diet seems to be made up of gastropods, invertebrates (including beetles, flies, lepidopterans, dragonflies, and caddisflies), crustaceans, worms, many varieties of seeds and plant matter, and roots and tubers. During the breeding season, male birds were recorded to have eaten 37.6% animal matter and 62.4% plant matter, most notably Echinochloa crus-galli, and nonlaying females ate 37.0% animal matter and 63.0% plant matter, while laying females ate 71.9% animal matter and only 28.1% plant matter. Plants generally make up the larger part of a bird’s diet, especially during autumn migration and in the winter.

The mallard usually feeds by dabbling for plant food or grazing; there are reports of it eating frogs. However, in 2017 a flock of mallards in Romania were observed hunting small migratory birds, including grey wagtail and black redstart, the first documented occasion they had been seen attacking and consuming large vertebrates. It usually nests on a river bank, but not always near water. It is highly gregarious outside of the breeding season and forms large flocks, which are known as sords.

Breeding

Mallards usually form pairs (in October and November in the Northern Hemisphere) until the female lays eggs at the start of the nesting season, which is around the beginning of spring. At this time she is left by the male who joins up with other males to await the moulting period, which begins in June (in the Northern Hemisphere). During the brief time before this, however, the males are still sexually potent and some of them either remain on standby to sire replacement clutches (for female mallards that have lost or abandoned their previous clutch) or forcibly mate with females that appear to be isolated or unattached regardless of their species and whether or not they have a brood of ducklings.

Egg clutches number 8–13 creamy white to greenish-buff eggs free of speckles. They measure about 58 mm (2.3 in) in length and 32 mm (1.3 in) in width. The eggs are laid on alternate days, and incubation begins when the clutch is almost complete. Incubation takes 27–28 days and fledging takes 50–60 days. The ducklings are precocial and fully capable of swimming as soon as they hatch. However, filial imprinting compels them to instinctively stay near the mother, not only for warmth and protection but also to learn about and remember their habitat as well as how and where to forage for food. When ducklings mature into flight-capable juveniles, they learn about and remember their traditional migratory routes (unless they are born and raised in captivity).

During the breeding season, both male and female mallards can become aggressive, driving off competitors to themselves or their mate by charging at them. Males tend to fight more than females, and attack each other by repeatedly pecking at their rival’s chest, ripping out feathers and even skin on rare occasions.

The drakes that end up being left out after the others have paired off with mating partners sometimes target an isolated female duck, even one of a different species, and proceed to chase and peck at her until she weakens, at which point the males take turns copulating with the female. Lebret (1961) calls this behaviour «Attempted Rape Flight», and Stanley Cramp and K.E.L. Simmons (1977) speak of «rape-intent flights». Male mallards also occasionally chase other male ducks of a different species, and even each other, in the same way. In one documented case of «homosexual necrophilia», a male mallard copulated with another male he was chasing after the chased male died upon flying into a glass window. This paper was awarded an Ig Nobel Prize in 2003.

Mallards are opportunistically targeted by brood parasites, occasionally having eggs laid in their nests by redheads, ruddy ducks, lesser scaup, gadwalls, northern shovellers, northern pintails, cinnamon teal, common goldeneyes, and other mallards. These eggs are generally accepted when they resemble the eggs of the host mallard, but the hen may attempt to eject them or even abandon the nest if parasitism occurs during egg laying.

Predators and threats

Mallards of all ages (but especially young ones) and in all locations must contend with a wide diversity of predators including raptors, mustelids, corvids, snakes, raccoons, opossums, skunks, turtles, large fish, felids, and canids, including domesticated ones. The most prolific natural predators of adult mallards are red foxes(which most often pick off brooding females) and the faster or larger birds of prey, i.e. peregrine falcons, Aquila eagles, or Haliaeetus eagles. In North America, adult mallards face no fewer than 15 species of birds of prey, from northern harriers and short-eared owls (both smaller than a mallard) to huge bald and golden eagles, and about a dozen species of mammalian predator, not counting several more avian and mammalian predators who threaten eggs and nestlings.

Mallards are also preyed upon by other waterside apex predators, such as the grey heron, European herring gull, the wels catfish, and the northern pike. Crows (Corvus spp.) are also known to kill ducklings and adults on occasion. Also, mallards may be attacked by larger anseriformes such as swans (Cygnus spp.) and geeseduring the breeding season, and are frequently driven off by these birds over territorial disputes. Mute swans (Cygnus olor) have been known to attack or even kill mallards if they feel that the ducks pose a threat to their offspring.

The predation-avoidance behavior of sleeping with one eye open, allowing one brain hemisphere to remain aware while the other half sleeps, was first demonstrated in mallards, although it is believed to be widespread among birds in general.

Status and conservation

Since 1998, the mallard has been rated as a species of least concern on the IUCN Red List of Endangered Species. This is because it has a large range–more than 20,000,000 km² (7,700,000 mi²) –and because its population is increasing, rather than declining by 30% over ten years or three generations and thus is not warranted a vulnerable rating. Also, the population size of the mallard is very large.

Unlike many waterfowl, mallards have benefited from human alterations to the world – so much so that they are now considered an invasive species in some regions. They are a common sight in urban parks, lakes, ponds, and other man-made water features in the regions they inhabit, and are often tolerated or encouraged in human habitat due to their placid nature towards humans and their beautiful and iridescent colours. While most are not domesticated, mallards are so successful at coexisting in human regions that the main conservation risk they pose comes from the loss of genetic diversity among a region’s traditional ducks once humans and mallards colonise an area. Mallards are very adaptable, being able to live and even thrive in urban areas which may have supported more localised, sensitive species of waterfowl before development. The release of feral mallards in areas where they are not native sometimes creates problems through interbreeding with indigenous waterfowl. These non-migratory mallards interbreed with indigenous wild ducks from local populations of closely related species through genetic pollution by producing fertile offspring. Complete hybridisation of various species of wild duck gene pools could result in the extinction of many indigenous waterfowl. The wild mallard itself is the ancestor of most domestic ducks, and its naturally evolved wild gene pool gets genetically polluted in turn by the domesticated and feral populations.

Over time, a continuum of hybrids ranging between almost typical examples of either species develop; the speciation process is beginning to reverse itself. This has created conservation concerns for relatives of the mallard, such as the Hawaiian duck, the New Zealand grey duck (A. s. superciliosa) subspecies of the Pacific black duck, the American black duck, the mottled duck, Meller’s duck, the yellow-billed duck, and the Mexican duck, in the latter case even leading to a dispute as to whether these birds should be considered a species (and thus entitled to more conservation research and funding) or included in the mallard species. Ecological changes and hunting have also led to a decline of local species; for example, the New Zealand grey duck population declined drastically due to overhunting in the mid-20th century. Hybrid offspring of Hawaiian ducks seem to be less well adapted to native habitat, and using them in re-introduction projects apparently reduces success. In summary, the problems of mallards «hybridising away» relatives is more a consequence of local ducks declining than of mallards spreading; allopatric speciation and isolating behaviour have produced today’s diversity of mallard-like ducks despite the fact that, in most, if not all, of these populations, hybridisation must have occurred to some extent.

Invasiveness

Mallards are causing severe «genetic pollution» to South Africa’s biodiversity by breeding with endemic ducks even though the Agreement on the Conservation of African-Eurasian Migratory Waterbirds – an agreement to protect the local waterfowl populations – applies to the mallard as well as other ducks. The hybrids of mallards and the yellow-billed duck are fertile, capable of producing hybrid offspring. If this continues, only hybrids occur and in the long term result in the extinction of various indigenous waterfowl. The mallard duck can cross breed with 63 other species, posing a severe threat to indigenous waterfowl’s genetic integrity. Mallards and their hybrids compete with indigenous birds for resources, including nest sites, roosting sites, and food.

Availability of mallards, mallard ducklings, and fertilised mallard eggs for public sale and private ownership, either as livestock or as pets, is currently legal in the United States except for the state of Florida, which has currently banned domestic ownership of mallards. This is to prevent hybridisation with the native mottled duck.

The mallard is considered an invasive species in New Zealand, where it competes with the local New Zealand grey duck, which was overhunted in the past. There, and elsewhere, mallards are spreading with increasing urbanisation and hybridising with local relatives.

The Eastern or Chinese spot-billed duck is currently introgressing into the mallard populations of the Primorsky Krai, possibly due to habitat changes from global warming. The Mariana mallard was a resident allopatric population – in most respects a good species – apparently initially derived from mallard-Pacific black duck hybrids; unfortunately, it became extinct in the late 20th century.

The Laysan duck is an insular relative of the mallard, with a very small and fluctuating population. Mallards sometimes arrive on its island home during migration, and can be expected to occasionally have remained and hybridised with Laysan ducks as long as these species have existed. However, these hybrids are less well adapted to the peculiar ecological conditions of Laysan Island than the local ducks, and thus have lower fitness. These ducks were found throughout the Hawaiian archipelago before 400 AD, after which they suffered a rapid decline during the Polynesian colonisation. Now, their range includes only Laysan Island. It is one of the successfully translocated birds, after having become nearly extinct in the early 20th century.

Relationship with humans

Domestication

Mallard have often been ubiquitous in their regions among the ponds, rivers, and streams of human parks, farms, and other man-made waterways – even to the point of visiting water features in human courtyards.

Mallard have had a long relationship with humans. Almost all domestic duck breeds derive from the mallard, with the exception of a few Muscovy breeds. Mallards are generally monogamous while domestic ducks are mostly polygamous. Domestic ducks have no territorial behaviour and are less aggressive than mallards. Domestic ducks are mostly kept for meat, as their eggs have a strong flavor. They were first domesticated in Southeast Asia at least 4000 years ago, during the Neolithic Age, and were also farmed by the Romans in Europe, and the Malays in Asia. It is also common for mallards to mate with domestic ducks and produce hybrid offspring that are fully fertile. Due to this, mallards have been found to be contaminated with the genes of the domestic duck.

Hunting

Mallards are one of the most common varieties of ducks hunted as a sport. The ideal location for hunting mallards is considered to be where the water level is somewhat shallow. Hunting mallards might cause the population to decline in some places, at some times, and with some populations. In certain countries, the mallard may be legally shot but is protected under national acts and policies. For example, in the United Kingdom, the mallard is protected under the Wildlife and Countryside Act 1981, which restricts certain hunting methods or taking or killing mallards.

As food

Since ancient times, the mallard has been eaten as food. The wild mallard was eaten in Neolithic Greece. Usually, only the breast and thigh meat is eaten. It does not need to be hung before preparation, and is often braised or roasted, sometimes flavoured with bitter orange or with port.

Wikipedia/eBird/xeno-canto