Nombre en español: Carpintero de Robledales
Nombre cientifico: Melanerpes formicivorus
Nombre en ingles: Acorn Woodpecker
Foto: Mauricio Ossa
El carpintero bellotero (Melanerpes formicivorus) es un pájaro carpintero de tamaño medio.
Los adultos tienen la cabeza, el dorso, las alas y la cola negras; la frente, la garganta, el vientre y el manto, blancos. Sus ojos son también blancos. Los machos adultos tienen el píleo completamente rojo mientras que las hembras presentan una franja negra entre la frente blanca y el píleo rojo.
Habitan en robledales, desde el sur de los Estados Unidos hasta Colombia. Anidan en árboles o ramas muertas, en grandes cavidades excavadas por la pareja. En la cría suelen participar varios individuos adultos: los estudios de campo muestran que estos grupos pueden estar constituidos por parejas criadoras monógamas o hasta por colectivos de siete machos y tres hembras (con más de 10 ayudantes no criadores).
Los grupos criadores crean auténticas despensas en las que acumulan bellotas: excavan agujeros en los árboles muertos y las almacenan allí. Estas bellotas quedan a la vista, así que el grupo va a defender el árbol de posibles robos. Las bellotas constituyen una parte importante de su dieta; también comen insectos que capturan de la corteza de los árboles o que atrapan en vuelo, además de frutos, semillas y, a veces, savia.
Es una especie residente permanente. Pero, si no hay bellotas disponibles pueden emigrar a otra área.
Anualmente pueden cavar 60,000 agujeros en un árbol con bellotas e incluso lo introducen en distintos para cubrirlo completo así evitarán que otro individuo se los hurte.
The acorn woodpecker (Melanerpes formicivorus) is a medium-sized woodpecker, 21 cm (8.3 in) long, with an average weight of 85 g (3.0 oz).
The adult acorn woodpecker has a brownish-black head, back, wings and tail, white forehead, throat, belly and rump. The eyes are white. There is a small part on the small of their backs where there are some green feathers. The adult male has a red cap starting at the forehead, whereas females have a black area between the forehead and the cap. The white neck, throat, and forehead patches are distinctive identifiers. When flying, they take a few flaps of their wings and drop a foot or so. White circles on their wings are visible when in flight. Acorn woodpeckers have a call that is almost like they are laughing.
The breeding habitat is forested areas with oaks in the hills of coastal areas and foothills of California and thesouthwestern United States south to Colombia. This species may occur at low elevations in the north of its range, but rarely below 1,000 m (3,300 ft) in Central America, and it breeds up to the timberline. The breeding pair excavate a nest in a large cavity in a dead tree or a dead part of a tree. A group of adults may participate in nesting activities: field studies have shown that breeding groups range from monogamous pairs to breeding collectives of seven males and three females, plus up to 10 nonbreeding helpers. Young from a single brood have been found with multiple paternity.
Food and homes
Acorn woodpeckers, as their name implies, depend heavily on acorns for food. In some parts of their range (e.g., California), the woodpeckers create granaries or «acorn trees» by drilling holes in dead trees, dead branches, telephone poles, and wooden buildings. The woodpeckers then collect acorns and find a hole that is just the right size for the acorn. As acorns dry out, they are moved to smaller holes and granary maintenance requires a significant amount of the bird’s time. They also feed on insects, sap, and fruit.
Defense and storing
The acorns are visible, and the group defends the tree against potential cache robbers like Steller’s jays and western scrub jays. Acorns are such an important resource to the California populations that acorn woodpeckers may nest in the fall to take advantage of the fall acorn crop, a rare behavior in birds. Acorn woodpeckers can also be seen sallying from tree limbs to catch insects, eating fruit and seeds, and drilling holes to drink sap. The acorn woodpecker will use any human-made structures to store acorns, drilling holes into fence posts, utility poles, buildings, and even automobile radiators. Occasionally the woodpecker will put acorns into places where it cannot get them out. Woodpeckers put 220 kg (490 lb) of acorns into a wooden water tank in Arizona. In parts of its range the acorn woodpecker does not construct a «granary tree», but instead stores acorns in natural holes and cracks in bark. If the stores are eaten, the woodpecker will move to another area, even going from Arizona to Mexico to spend the winter.
Acorn woodpeckers practice cooperative breeding, which is a relatively rare evolutionary trait that is thought to occur in only nine percent of bird species. Cooperative breeding is defined as more than two birds taking care of nestlings in the nest. With the acorn woodpecker, cooperative breeding occurs in two ways: coalitions and family groups. Coalitions of adult acorn woodpeckers nest together, localizing to storage granaries.Additionally, adult offspring often stay in their parents’ nest and help raise the next generation of woodpeckers. It is generally believed that limited territories drive cooperative breeding behavior in birds, and in the case of the acorn woodpecker, this limited territory is the acorn storage granary.
As mentioned, adult acorn woodpeckers live together in «coalitions», which consist of up to seven co-breeding males and up to three joint-nesting females; however, most nests are made up of only three males and two females. Nesting groups can also contain up to ten offspring helpers. Interestingly, these breeding coalitions are typically closely related. The males are often brothers, and the females are usually sisters. Inbreeding is rare, however, meaning that co-breeders of the opposite sex are almost never related.
In groups with more than one breeding female, the females put their eggs into a single nest cavity. A female usually destroys any eggs in the nest before she starts to lay. Once all the females start to lay, they stop removing eggs.
Threats and degradation
Acorn woodpeckers, like many other species, are threatened by habitat loss and degradation. Competition for nest cavities by non-native species is an ongoing threat in urbanized areas. Conservation of this species is dependent on the maintenance of functional ecosystems that provide the full range of resources upon which the species depends. These include mature forests with oaks capable of producing large mast crops and places for the woodpeckers to nest, roost, and store mast. Residents are encouraged to preserve mature oak and pine-oak stands of trees and to provide dead limbs and snags for nesting, roosting, and granary sites to help preserve the acorn woodpecker’s population.
Walter Lantz is believed to have patterned the call of his cartoon character Woody Woodpecker on that of the acorn woodpecker, while patterning his appearance on that of the pileated woodpecker which has a prominent crest.