Nombre en español: Arrocero Norteño
Nombre en inglés: Dickcissel
Nombre científico: Spiza americana
El arrocero americano (Spiza americana) también denominado arrocero norteño, gorrión de pecho amarillo, sabanero americano, sabanero arrocero y sabanero común, es una especie de ave paseriforme de la familia de los cardinálidos. Anteriormente, se incluyó dentro de la familia Emberizidae. Es el único representante del género Spiza.
Es de hábitos migratorios, anida en el centro-sur de Canadá y en la parte central de los Estados Unidos, y pasa el invierno en México, Centro y Sudamérica.
Su nombre Spiza deriva del griego y significa Pinzón mientras que el epíteto americana se estableció haciendo referencia al continente americano.
El adulto mide unos 15 cm. Posee un pico grueso, triangular, gris-azulado pálido. Ambos sexos presentan la cabeza gris, con ceja amarilla y garganta amarilla y blanca. El dorso, rabadilla, alas y cola son pardos, con listas longitudinales negruzcas.
Los machos, en época reproductiva, se distinguen por una «barbilla» negra en el área de la garganta, que se desvanece en otoño e invierno; además, tienen el pecho amarillo brillante y el vientre blanquecino, con flancos grisáceos. El patrón de coloración, aunque no la anatomía, recuerda al del pradero Sturnella magna.
La hembra es bastante parecida a la hembra del gorrión doméstico (Passer domesticus). Se distingue por ser más pálida, por la lista infraocular blanca, el pico gris-azulado, y manchas amarillentos en el pecho.
Distribución y hábitat
Se reproduce desde el centro-sur de Canadá (provincia de Ontario) y la parte central de los Estados Unidos, entre las Montañas Rocosas y los Apalaches. En invierno migra en grandes bandadas hacia México —donde se vuelve abundante en particular en el sur—, Centroamérica y el norte de América del Sur (norte de Colombia, norte de Venezuela y Guyana). También puede registrarse casualmente en las Antillas y en Ecuador.
Se alimentan de insectos y semillas. Prefiere terrenos abiertos donde sean abundantes los pastizales. En su área de invernada, habita terrenos bajos de clima tropical, siendo muy abundante en campos de cultivo, sobre todo en arrozales, lo que le ha valido el nombre de arrocero. Puede ser nocivo para la agricultura y en algunas regiones se le considera una plaga.
En Colombia se encuentra hasta 1600 m de altura sobre el nivel del mar desde límites con Panamá y desde allí hacia el oriente por las tierras bajas del norte del país hasta el oriente de la Guajira y hacia el sur hasta el valle medio del río Magdalena. También se encuentra al oriente de los Andes desde el suroriente de Boyacá hasta el sur del Meta.
Durante el periodo reproductivo se alimenta de semillas y artrópodos como saltamontes, orugas, mosquitos, arañas y escarabajos. En las áreas invernales come principalmente semillas de pastos, arroz y sorgo y en menor proporción insectos y arañas.
Se reproduce en Norteamérica entre mayo y agosto o septiembre. El macho puede ser polígamo y la cantidad de parejas que tenga puede estar relacionado con la calidad de su territorio. El nido es construido completamente por la hembra, tiene forma de copa y para su construcción utiliza tallos de pastos, hojas y lo recubre con pastos más finos, pelo de caballo y raíces. Generalmente lo sitúa a baja altura sobre vegetación herbácea y en él pone de 3 a 6 huevos de color azul pálido, los cuales también son incubados únicamente por la hembra durante 12 a 13 días. Las crías está listas para abandonar el nido entre el día 8 a 10 después de la eclosión y la hembra los sigue alimentando alrededor de dos semanas más. Se ha encontrado que los nidos son frecuentemente parasitados por (Molothrus ather).
Es una especie migratoria que se desplaza desde Norteamérica hacia Centroamérica y Suramérica a pasar el periodo invernal. Tiene el hábito frecuente de reunirse en bandadas de varios centenares o miles en áreas de alimentación.
The dickcissel (Spiza americana) is a small American seed-eating bird in the family Cardinalidae. It is the only member of the genus Spiza, though some sources list another supposedly extinct species (see below).
Male in nonbreeding plumage – Maywood, IllinoisMale in nonbreeding plumage – Ouachita National Forest
Dickcissels have a large pale bill, a yellow line over the eye, brownish upperparts with black streaks on the back, dark wings, a rust patch on the shoulder and light underparts. Adult males have a black throat patch, a yellow breast and grey cheeks and crown. This head and breast pattern is especially brilliant in the breeding plumage, making it resemble an eastern meadowlark. Females and juveniles are brownish on the cheeks and crown and are somewhat similar in appearance to house sparrows; they have streaked flanks.
In flight they make a low, «electric», buzzing fpppt. From an open perch in a field, this bird’s song is a sharp dick dick followed by a buzzed cissel, also transcribed as skee-dlees chis chis chis or dick dick ciss ciss ciss.
Systematics and taxonomy
The dickcissel is part of a group of Cardinalidae that apparently also includes Amaurospiza, Cyanocompsa, Cyanoloxia and Passerina. Spiza is the only one among these that lacks blue structural colors in its plumage. Though the color pattern and habits of the dickcissel make it stand apart from other Cardinalidae, its robust cone-shaped bill – stouter than in American sparrows or true finches which it somewhat resembles at first glance – gives away its relationships.
The scientific name of the dickcissel means simply «American finch». Furthermore, its genus name Spiza derives from the Ancient Greek word σπίζα (spíza), a catch-all term for finch-like birds. Many bird genera contain the suffix -spiza, but none of these were generally held to be a really close relative of Spiza itself. Amusingly, Amaurospiza seems to have turned out to be one of the closest living relatives of the dickcissel after all.
A problematic specimen is often discussed under the name of Spiza townsendi (or Spiza townsendii, the original misspelt specific name proposed by John James Audubon). This individual was collected on May 11, 1833, by Audubon’s colleague John Kirk Townsend in New Garden Township, Chester County, Pennsylvania. The specimen remains unique and nothing is known about what it represents with certainty; it had thus even been suggested to be an extinct relative. In 2014, Kyle Blaney photographed the bird in Ontario, proving its continuing existence.
It is commonly called «Townsend’s dickcissel» (or «Townsend’s bunting», «Townsend’s finch») in reference to the collector whom the scientific name honors. Rather than a distinct species or subspecies, it is (as certainly as this can be said in absence of direct proof) a color variant. Comparing the birds, it is immediately obvious that the yellow lipochrome pigments are entirely absent in «Townsend’s dickcissel». The specimen has foxed today, giving it an altogether beige hue, but when originally shot, the olive areas of the head were grey as the cheeks, and the yellow and buff on face and underside was pure white. The brown wings and tail were rufous, due to the pheomelanins not being tinged by lipochromes.
A color mutation?
Thus, this bird is very likely certainly the result of a simple genetic change, perhaps just a single point mutation, affecting some part of the carotinoid metabolism – essentially the same thing that happens in albinism but in a different metabolic pathway. Though the bird seemed to be healthy and had survived to maturity when it found its untimely end through Townsend’s gun, no other such specimens have been documented before, nor ever since. Albinism and other pigment aberrations are not infrequently seen in birds, and the lack of further specimens is somewhat puzzling in that respect.
No specific details are known about the dickcissel’s lipochrome metabolism; it may be that it happens to be more fine-tuned than in other birds, so that most mutations therein will be lethal and Audubon’s bird was simply one of the very few individuals that survived. It stands to note that in wild birds, varying from species to species some color aberrations are less frequently seen than others, and that in captive birds such as canaries, some color mutations have only arisen a handful of times at most during several centuries of dedicated breeding and screening for novel color variants (see also Budgerigar colour genetics). While only a complete molecular biological study of the dickcissel’s metabolism and the specimen’s ancient DNA stands any reasonable chance to resolve the question with certainty, the hypothesis of an extremely uncommon color mutation is plausible, and such phenomena certainly occur in other Passeroidea.
Alternatively, the bird was considered a hybrid, but the present state of knowledge of the dickcissel’s relations makes this not very plausible – there are a number of species with which Spiza could conceivably produce hybrids – such as Passerina – but the lack of even the slightest hint of blue structural colors in Townsend’s specimen and it moreover being not different from a dickcissel in habitus makes the hybrid theory suspect. Regardless, Townsend noted observed the bird making vocalizations reminiscent more of an indigo bunting (Passerina cyanea), and by comparing mitochondrial and nuclear DNA sequences of the specimen with those of the dickcissel, the indigo bunting, and perhaps other Passerina, the hybridization hypothesis should be far more easy to prove or reject than a color aberration. On the other hand, there is not enough known on whether dickcissels pick up their characteristic vocalizations from conspecific males or whether they are innate, and thus no firm conclusion regarding Townsend’s observations has been made.
Their breeding habitat is fields in midwestern North America. They migrate in large flocks to southern Mexico, Central America, and northern South America. They may occur as vagrants well outside of their normal range.
Dickcissels forage on the ground or in fields. They mainly eat insects and seeds. Outside of the nesting season, they usually feed in flocks. They are considered a pest by farmers in some regions because flocks can consume large quantities of cultivated grains.
The birds migrate to their breeding range rather late, with the first arriving only in May, with most birds only arriving in early June. They nest near the ground in dense grasses or small shrubs, or up to 3–4 ft (91–122 cm) high in bushes and trees. Males may have up to six mates, with most attracting only one or two, and several failing to attract any mates at all. Yet if such «bachelors» survive until next summer, they will get another try to attract females, as the partners only stay together for raising one brood. Dickcissels are thus among the few songbirds that are truly polygynous. When they leave for winter quarters by early August or so, what little pair bond existed during the summer is broken up.
Dickcissel populations frequently fluctuate in numbers, even to the extent that their range changes notably. In the early 19th century, dickcissels expanded eastward, establishing a population in New England and the mid-Atlantic states that disappeared around the end of the century. Both appearance and disappearance were probably related to changes in land use.
The Dickcissel is one of the most typical and abundant breeding birds of North American prairie grasslands, with a primary breeding range (Fig. 1) centered, almost bull’s-eye-like, on that biome. Despite this biogeographic affinity, this species is notorious for regular seasonal movements within its primary breeding range and for irregular movements outside of this core range to breed in surrounding areas where extensive grassland habitat exists. These erratic, semi-nomadic movements result in dramatic year-to-year changes in distribution and abundance, especially in peripheral and sporadically occupied areas. Most Dickcissels winter in the llanos region (seasonally flooded grasslands and savannas) of central Venezuela, but again, some birds move around the winter range and occasionally spend part or all of the nonbreeding season in other areas of Central and South America.
On both breeding and nonbreeding ranges, the Dickcissel has had to adjust to major habitat changes, as natural grasslands and savannas have been largely replaced by agriculture, but it seems to have adapted well to many secondary habitats, and even thrives in some agricultural landscapes. The species has been quite well studied on both its breeding and nonbreeding ranges for several reasons: It shows unusual, at times almost nomadic, shifts in distribution. and abundance within its breeding and wintering ranges (Gross 1921, 1968; Fretwell 1986); it has a polygynous mating system (Zimmerman 1966b); it forms huge flocks and roosts during the nonbreeding season (Basili and Temple 1999a); it is a pest on agricultural crops throughout its winter range, especially in Venezuela (Basili and Temple 1995, 1998); and it is of conservation concern, having suffered severe population declines (Fretwell 1977, 1979; Basili and Temple 1995). Most recent and ongoing studies on the breeding range have been motivated by interests in how changing land-use practices (for example, large-scale restoration of grassland through the Conservation Reserve Program) in the core breeding range affect nesting birds. On the winter range, most recent and ongoing research has focused on the bird’s relationship with cereal crops and how to lessen the impacts of lethal control efforts undertaken by aggrieved farmers. Still, as this review ill reveal, many aspects of its biology remain unstudied.
Fuentes: Wikipedia/eBird/xeno-canto/WikiAves/Neotropical Birds