Acorn woodpecker

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Acorn woodpecker
Acorn woodpecker ♂ (Melanerpes formicivorus)

Acorn woodpecker ♂ ( Melanerpes formicivorus )

Systematics
Order : Woodpecker birds (Piciformes)
Family : Woodpeckers (Picidae)
Subfamily : Real woodpeckers (Picinae)
Genre : Melanerpes
Type : Acorn woodpecker
Scientific name
Melanerpes formicivorus
( Swainson , 1827)

The acorn woodpecker ( Melanerpes formicivorus ) is a medium member of the genus Melanerpes within the subfamily of the Real woodpecker (Picinae). The conspicuous and not uncommon species is distributed from southwest Washington southwards to northwestern South America. Like some other Melanerpes species, acorn woodpeckers mostly live in family groups in which a highly differentiated social structure is developed. The geographical variation is great: over ten subspecies are described, seven of which are generally recognized. Almost all subspecies are resident birds and have an intensive autumn stockkeeping.

features

Acorn woodpeckers are about the size of a spotted woodpecker with a length of 22–24 centimeters . If there is sufficient light, they are not to be confused with any other species of woodpecker in their habitat.

The back and upper elytra are glossy black; Depending on the incidence of light, these body parts are iridescent green, bluish or purple. The rump and the under-tail-coverts are clearly dashed in black on a white background. The arm and hand wings are largely dull black on the upper side, a white spot is visible in the area of ​​the bases of the hand wings. The under wing-coverts are black and have fine white dots, the underside of the arm and hand wings is duller black or brown-black. The two central control springs are elongated and taper to a point; often, especially in young individuals, they show fine white or golden yellow inclusions. In some birds, the bases of the tail feathers are white.

Differentiation of males and females

The drawing and coloring of the head and face are quite clearly differentiated between the sexes. In the male, the vertex and the upper neck area are brightly scarlet; A black field stretches from the lower neck in an arc over the eye, which is markedly bordered by the white of the rest of the face. The black beak is surrounded by a black area at the base; the upper part of the throat is also black. The chest and lower throat area are whitish or yellowish-white. The blackish breast plumage shows a clear white markings, in some subspecies there are also red feathers. The iris is white. In females, the scarlet spot is limited to the back of the apex and upper neck area. Towards the forehead, it is separated from the white plumage of the forehead by a black band. In the male, the red of the parting borders directly on the white of the forehead area. Feet and toes are dark gray. Males are slightly larger and heavier than females.

The youth plumage is similar to the adult plumage, but the black parts of the plumage are somewhat lighter and largely lackluster. The chest area is often brownish, the iris is black. Sexing young birds is difficult because males and females have the same size red headstock. At the end of the first year of life, acorn woodpeckers molt into adult plumage.

The flight is a typical arch flight for woodpeckers, with the wings being placed close to the body in the trough of the waves. In addition to the characteristic facial markings, the white rump and the white wing fields in the area of ​​the hand swing bases are distinctive identification marks.

voice

Family groups of the acorn woodpecker are acoustically very noticeable all year round, while individual couples behave significantly more quietly. The most common utterances are the welcome call , which is often transcribed as Wäke-wäke , and an also two-syllable element, usually presented in a row , which can be described as Jäk-up and is uttered above all in antagonistic situations. A number of croaking and screeching sounds can also be heard. The drum rolls are relatively slow; they consist of up to 20 individual elements.

distribution and habitat

Distribution of the acorn woodpecker

The distribution area of ​​the acorn woodpecker extends from western North America near the Pacific to the south over large parts of Mexico and Central America to the northern Andean regions of Colombia . The northernmost occurrences are small, isolated populations in southern Washington; the breeding areas in Oregon and northern California are fragmented and patchy . To the south and southeast, suitable low mountain range and mountain regions are populated almost everywhere. There are two small isolated deposits on Baja California . To the southeast, the acorn woodpecker is found in the mountainous regions of Arizona and New Mexico and sparsely distributed in western and central Texas . In Mexico, the species mainly inhabits the light oak forests of the western coastal mountains and the mountainous regions of the eastern and southern Sierra Madre . In Central America, the occurrences are largely limited to mountain regions. Largely isolated from these more or less closed distribution areas, the species breeds in the Maya Mountains in southern Belize , in the adjacent Guatemalan areas and in the central mountainous region of Panama . On the northern and central slopes of the Andes in Colombia, there are widely separated breeding populations.

Since acorn woodpeckers roam far when there is a lack of food, they occasionally establish breeding sites far away from the closed habitat. In the United States, a small population currently forms the westernmost outpost on Santa Catalina , and one in Kerr County , Texas, the southeasternmost.

Valley oak , an important food and breeding tree in the lowlands

Preferred habitats of the species are loosened oak forests and oak-pine mixed forests . The species also penetrates along rivers, which are mainly populated with poplar species , into semi-arid areas and colonizes large parks, cemeteries or other anthropogenic landscapes, as long as there are enough acorns available as winter food. In the northernmost distribution areas the acorn woodpecker breeds in pure conifer stands, in the south in tropical hardwood trees. In southern Central America and Colombia, the connection to oaks as a food tree is also present, but not as exclusive as in the northern part of the distribution area. In addition to oaks, on whose fruits many acorn woodpecker populations are very dependent, an optimal habitat must provide a sufficient supply of ants and other insects, as well as dead trees or at least strong dead branches in which nesting and sleeping caves can be built. Also in Colombia, where flying insects, fruits and tree sap are available all year round, and the fruits of the only oak species found there are only of minor importance for the species’s nutrition, oak trees, the so-called Robledales , are preferred habitats.

Acorn woodpeckers are mainly breeding birds of the low mountain ranges and the montane zones. In many areas of their range they rise up to the natural limit of their breeding and food trees, in Colombia up to over 3500 meters. In southern Central America and Colombia, the species below 1500 meters is largely absent. Acorn woodpeckers breed in low-lying areas near the coast only in parts of California, on the Baja California and on the southwest slopes of the Sierra Madre del Sur.

Space requirements and territoriality

Acorn woodpeckers are territorial throughout the year. However, the size of the individual territories is extremely different. In favorable areas it is less than 10 hectares, in suboptimal regions the districts are many times larger. The entire family association defends the key points against conspecifics, these are the breeding and sleeping caves, the reservoirs and the food and sap trees. In addition to conspecifics, direct cave or food competitors are also driven out of the vicinity of these places. Other species of woodpecker, crows , owls and starlings are vigorously attacked throughout the year, and acorn woodpeckers are also aggressive towards the squirrels found in their habitat . Other bird species are mostly tolerated, even if they use the same food resources. In Central America, communities of quetzals , toucans and acorn woodpeckers were often observed eating fruit.

hikes

Most populations of the acorn woodpecker are resident birds . Only when the reservoirs are exhausted do they leave their breeding area and usually roam around in small areas. Only if acorns are poorly available in a large area, hikes over a few 100 kilometers are also possible. Such situations can lead to so-called wandering years, in which family groups wander far and wide without brooding. They can then also be found in areas where they are otherwise absent.

Only one population widespread in the Huachuca Mountains in southeastern Arizona has developed a different behavior. The woodpeckers in this isolated region do not store a large number of acorns, but only store a few acorns in cracks in the bark or other crevices. These supplies will soon run out. After that, all acorn woodpeckers leave the area and move to the loose oak forests of the eastern Sierra Madre in Mexico. In spring they return to their traditional breeding area.

Food and subsistence

Acorn woodpeckers feed on both animal and vegetable food. The vegetable content is higher, although insects are preferred if they are available. In addition to ants , especially swarming sex animals, various types of butterflies , flies , lice and cicadas as well as beetles and bugs are preyed on; the quantitative composition varies and depends on the seasonal and regional availability of the prey. Wood-dwelling beetle larvae play no role in the food spectrum of the species. In addition, acorn woodpeckers occasionally prey on small lizards , mammals , young birds and bird eggs.

The vegetable part of the diet consists mainly of acorns from different oak species, which in many populations accounts for more than half of the food energy consumed. In addition, various nuts, in particular almonds and walnuts, pine seeds as well as fruits, berries and grass seeds are consumed. In late winter and early spring, tree sap is an important nutritional supplement. Only one oak species, Quercus humboldtii , occurs in the acorn woodpecker's habitat in Colombia . Acorns therefore do not play a major role there. Insects, fruits and tree sap predominate here all year round; occasionally flower nectar is also consumed.

Female acorn woodpecker on a storage tree

Acorn woodpeckers mainly hunt for their insect food on the fly. It is usually spotted from a raised hide and caught in a short excursion flight. Small prey animals are eaten immediately, larger ones are carried to a suitable smithy and processed there. Tree-dwelling insects can be read from the stem, branch or leaf surface, and loose pieces of bark are sometimes removed; the species also digs for hidden prey in cracks in the bark and cracks in wood. Real hacking was rarely seen. The woodpecker groups often stay in the upper trunk and crown area; acorn woodpeckers rarely appear on the ground. The fruit food is picked directly from the tree, acorns usually individually. He wins tree sap by drilling sap-bearing trunks and branches, whereby the holes in which the tree sap collects are distributed irregularly on trunks and branches. Oak species in particular are used as suppliers of juice. Almost all eating activities are group activities; differently toned Wäke calls can be heard continuously ; There is hardly any intraspecific aggression when eating.

Stock keeping

Almost all subspecies of the acorn woodpecker operate an intensive autumn storage. In some populations of the nominate form this is less pronounced for reasons not known so far, in the birds of the subspecies M. f. flavigula is largely absent. Characteristic for the species is the creation of special stores, known in English as granaries, in which thousands of acorn seeds can be stored. All species with thick bark can be used as storage trees. The holes are precisely adapted to the object to be saved; they do not penetrate into the cambium and do not harm the tree. Extensive reservoirs are the work of many generations of woodpeckers, because every single acorn woodpecker chops and drills only a few storage holes in an autumn and winter. Most of the holes are in the trunk area, often on the underside of strong side branches. Each group of woodpeckers maintains a main storage facility and some secondary storage facilities in their territory. In addition to acorns, nuts and pine seeds, and occasionally beetles, are also kept. In addition to the breeding caves, the storage areas are the centers of the district; they are vigorously defended by all family members.

behavior

Bathing female

social behaviour

Like some other species of this genus, acorn woodpeckers live in social associations. The theory that this social way of life can make the best possible use of a habitat that only provides limited resources ( habitat saturation ) is sometimes called into question again, since acorn woodpeckers also live in family groups in areas with abundant food. These groups consist of 2 to 15 members. The groups usually consist of 1–4 male breeders, 1–2 female breeders, with one usually acting as the main breeder, and 0–10 helpers of both sexes. The helpers are mostly the offspring from last year's broods. Female co-brooders lay their eggs in the brood cavity of the main female, which, however, carries them out of the cavity until laying begins, where they are then consumed by the family members. Male co-breeders copulate with other females, but rarely with the main female. Co-brooders are often disturbed by other males, especially the main male. Another vehement intraspecific aggression can occur if one main breeding partner dies during the breeding season and is replaced by another. This then almost always destroys the clutch or kills the nestlings. Even if all male or female breeders disappear or perish outside the breeding season and conspecifics try to close this gap from outside, there are intense, often several weeks-long conflicts between the remaining breeders and helpers and the intruders.

Outside of these reproductive situations, acorn woodpeckers live cooperatively in their family, but together with a certain distance. Most of the activities take place in the association, which is constantly connected by voice feeling. Hierarchical conflicts within a group were not observed.

Breeding behavior

Male acorn woodpecker feeds almost full-fledged nestling

Acorn woodpeckers become sexually mature at the end of their first year of life; a little over 31 percent of one-year-olds of both sexes start brooding at this age. In the second year of life, three quarters of all woodpeckers are breeders. In individual cases, however, non-breeding helpers can be over 5 years old. The mating systems in acorn woodpecker groups are variable. There can be a main pair that is largely monogamous, or a main breeder of different sexes who mate with the breeders of the opposite sex. Only one nesting cavity is built; female co-breeders lay their eggs in this too. The nest cavity is usually high on the trunk or a strong side branch of different tree species; it can lie in the tree in which the storerooms are located, but also up to a kilometer away from the pantry. Mostly dead trees are chosen, or at least previously damaged areas are exploited. For living trees, those with soft wood, especially poplar, are chosen. All group members participate in the construction of the cave, but the brooding ones more than the helpers. The nesting holes are used for several years, but new ones are built every year, so that a group of acorn woodpeckers almost always has enough nesting and sleeping holes.

The laying period is in Oregon and California in April and May, in Arizona a little later; in the Central American breeding areas between April and the start of the hurricane season in June. In Colombia, acorn woodpeckers breed in March and April. In the Californian coastal areas, acorn woodpeckers start a second brood when the acorn harvest is particularly good in late summer and autumn; in other regions, second broods are started within the same breeding cycle when the clutch is lost, regular second broods separated from the main cycle were only rarely observed.

The clutches are of different sizes depending on the number of second layers; on average, they contain 5 (4–9) pure white eggs. They are incubated for 11 days mainly by the egg-laying females and the brooding males. The share of helpers in the breeding business is low. After hatching, the nestlings are looked after by all group members. In all aspects of welfare, the proportion of egg-laying females outweighs that of brooding males; that of the helpers is the least, but not inconsiderable. After an average of 32 days, the young woodpeckers fly out and are provided with food by all group members for a longer period of time. The departure rate is a little over 60 percent on average; it is greatest in large family groups.

Systematics

The acorn woodpecker is a member of the genus Melanerpes in which 24 mostly medium-sized woodpeckers are summarized, whose range includes North, Central and South America as well as some of the Caribbean islands . At least eight of these species live permanently in social associations. Within this genus Melanerpes formicivorus ( Swainson , 1827) forms the tribe Melanerpini together with the blood-faced woodpecker and the red-headed woodpecker . The species shows largely clinical geographic variation in coloration of the throat, chest and cheeks. In addition, there are differences in the overall length, in the relative length of the tail and the beak. Based on these variables, seven subspecies are currently considered generally recognized. Genetic tests are still pending.

The nominate form is distributed from Arizona and New Mexico southwards to the isthmus of Tehuantepec . Individuals of this subspecies and the subspecies M. f. Living north and east of it . bairdi Ridgway , 1881 are the largest; the color of the throat is largely white, as is the anterior cheek area. Only a few red feathers are scattered in the breast plumage. In the southwestern United States, the two groups are separated by the Mohave .

The subspecies M. f , which occurs in isolation in southern Baja California, differs greatly . angustifrons S. F. Baird , 1870, in which the iris has a brownish hue and whose wing length is by far the smallest of all subspecies.

Melanerpes f. flavigula - male

The subspecies M. f., Which live isolated from one another in the mountainous countries of Central America . lineatus ( Dickey & Van Rossem , 1927) ( Oaxaca and Chiapas southwards to Nicaragua), M. f. albeolus Todd , 1910 (Southern Belize and Northeast Guatemala) and M. f. striatipectus Ridgway , 1874 ( mountainous countries in Costa Rica and mountainous regions in Panama ), are very similar in size and only slightly different in color. All have a relatively large proportion of red feathers in the black breast plumage.

M. f. striatipectus leads to the southernmost subspecies M. f. flavigula ( Malherbe , 1849), which occurs in isolation in some Andean regions of Colombia. In these birds, the field of vision is haze yellow, but the throat is rich yellow. In flavigula , only the males have a red head plate that is greatly reduced in size, while the vertex is black in the females. Together with angustifrons , the latter two subspecies are among the smallest representatives of this species.

Existence and endangerment

Birdlife International does not list the acorn woodpecker at any risk level. According to an estimate from 2003, the same source puts the total population at just over 3 million individuals. In many parts of its range, the acorn woodpecker is the most common type of woodpecker.

Individual evidence

  1. ↑ Peterson (1990) p. 222.
  2. ^ BNA (1995) Sounds
  3. ↑ a b Kattan (1988) p. 101.
  4. ↑ a b BNA (1995) Migration
  5. ^ BNA (1995) Dietary Preferences
  6. ↑ Kattan (1988) pp. 100-106.
  7. ↑ BNA (1995) Behavior
  8. ↑ BNA (1995) Demography and Population
  9. ↑ Mumme (1990) pp. 360-368.
  10. ↑ BNA (1995) Breeding
  11. ^ William Swainson, p. 439.
  12. ^ BNA (1995) Systematics
  13. ↑ Benítez-Díaz (1993) p. 64 f.
  14. ^ Robert Ridgway 1881, p. 85.
  15. ^ Spencer Fullerton Baird, p. 405.
  16. ↑ Donald Ryder Dickey et al. a., p. 1.
  17. ^ Walter Edmond Clyde Todd, p. 153.
  18. ^ Robert Ridgway (1874), p. 561.
  19. ^ Alfred Malherbe, p. 542.
  20. ↑ Benítez-Díaz (1993)
  21. ↑ Factsheet Birdlife Int. (2006)

literature

  • Hesiquio Benítez-Díaz: Geographic Variation in Coloration and Morphology of the Acorn Woodpecker. In: The Condor. 95 (1993) pp. 63-71.
  • Factsheet Birdlife Int. (engl.)
  • Philip N. Hooge, Mark T. Stanback, Walter D. Koenig: Nest-Site Selection in the Acorn Woodpecker. In: The Auk. 116/1 (1999) pp. 45-54.
  • Josep del Hoyo et al: Handbook of the Birds of the World. Volume 7: Jacamars to Woodpeckers. Lynx Edicions, 2002, ISBN 84-87334-37-7 (HBW).
  • Gustavo Kattan: Food Habits and Social Organization of Acorn Woodpecker in Colombia. In: The Condor. 90, 1988, pp. 100-106.
  • Walter D. Koenig, Peter B. Stacey, Mark T. Stanback, Ronald L. Mumme: Acorn Woodpecker (Melanerpes formicivorus). In: A. Poole (Ed.): The Birds of North America Online. Cornell Lab of Ornithology, Ithaca 1995. (Online version) = (BNA)
  • Ronald L. Mumme et al .: Individual Contributions to Cooperative Nest Care in the Acorn Woodpecker. In: The Condor . 92. 1990, pp. 360-368.
  • Roger Tory Peterson: Western Birds. Houghton Mifflin Company, Boston 1995, ISBN 0-395-51749-4 , p. 222.
  • Hans Winkler , David Christie, David Nurney: Woodpeckers. A Guide to Woodpeckers, Piculets, and Wrynecks of the World. Pica Press, Robertsbridge 1995, ISBN 0-395-72043-5 .
  • William Swainson: A Synopsis of the Birds discovered in Mexico by W. Bullock, FLS and HS, and Mr. William Bullock, jun. In: The Philosophical magazine: or Annals of chemistry, mathematics, astronomy, natural history and general science . tape 1 , no. 85 , 1827, pp. 433-442 ( online [accessed March 24, 2015]).
  • Alfred Malherbe: Description de quelques nouvelles espèces de Picinées (Picus, Linn.) . In: Revue et magasin de zoologie pure et appliquée (=  2 ). tape 1 , 1849, p. 529-544 ( online [accessed March 24, 2015]).
  • Donald Ryder Dickey, Adriaan Joseph van Rossem: Seven new birds from Salvador . In: Proceedings of the Biological Society of Washington . tape 40 , 1927, pp. 1-7 ( online [accessed March 24, 2015]).
  • Robert Ridgway in Spencer Fullerton Baird, Thomas Mayo Brewer, Robert Ridgway: A History of North American Birds . tape 2 (Land Birds). Little Brown and Company, Boston 1874 ( online [accessed March 24, 2015]).
  • Robert Ridgway: Nomenclature of North American Birds chiefly contained in the United Staes National Museum . In: Bulletin of the United States National Museum . No. 21 , 1881, p. 1-94 ( online [accessed March 24, 2015]).
  • Walter Edmond Clyde Todd: Two new woodpeckers from Central America . In: Proceedings of the Biological Society of Washington . tape 23 , 1910, pp. 153–155 ( online [accessed March 24, 2015]).
  • Spencer Fullerton Baird from a manuscript by James Graham Cooper: Ornithology . In: Geological Survey of California . tape 1 (Land birds), 1870, p. 153–155 ( online [accessed March 24, 2015]).

Web links

Commons : Melanerpes formicivorus  - album with pictures, videos and audio files