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 acorn woodpecker is a fascinating bird that was first formally described in 1827 by the English naturalist, William John Swainson. Swainson named the species Picus formicivorus after a specimen he collected in Mexico. The specific epithet combines the Latin words ‘formica’, meaning ant, and ‘vorus’, meaning eating, as this bird feeds on ants.
The type locality of the acorn woodpecker is Temascaltepec in Mexico, and it is one of 24 species now placed in the genus Melanerpes that was introduced by Swainson in 1832. Interestingly, within the genus Melanerpes, the acorn woodpecker is sister to a clade containing two South American species: the white woodpecker (Melanerpes candidus) and the white-fronted woodpecker (Melanerpes cactorum).
The acorn woodpecker has seven recognized subspecies, each with its unique range. These subspecies include M. f. bairdi, which is found from Oregon (USA) to north Baja California (Mexico), and M. f. angustifrons, which is found in south Baja California (Mexico). M. f. formicivorus is found in the southwest USA to southeast Mexico, while M. f. albeolus is found in east Chiapas (southeast Mexico) to Belize and northeast Guatemala. M. f. lineatus can be found in Chiapas (south Mexico) to north Nicaragua, and M. f. striatipectus is found in Nicaragua to west Panama. Finally, M. f. flavigula can be found in Colombia.
Overall, the acorn woodpecker is a unique and fascinating species, with its various subspecies adapting to different environments across North and South America.
The adult acorn woodpecker is a stunning bird with a striking appearance. Its head, back, wings, and tail are brownish-black, while its forehead, throat, belly, and rump are a dazzling white. Interestingly, the eyes of fledglings start off dark and gradually turn white within a few months. These birds also have a unique greenish patch of feathers on the small of their backs.
One of the most distinctive features of adult acorn woodpeckers is the red cap found on the males’ foreheads in most subspecies, while females have a black area between the forehead and the cap. Additionally, their white neck, throat, and forehead patches make them easily recognizable. When in flight, their wings display white circles, adding to their already captivating appearance.
If you’re lucky enough to hear an acorn woodpecker’s call, it almost sounds like they are laughing. It’s a sound that’s hard to forget once you’ve heard it.
In terms of measurements, adult acorn woodpeckers are typically between 19-23 cm (7.5-9.1 in) in length and weigh between 65-90 g (2.3-3.2 oz). Their wingspan ranges from 35-43 cm (14-17 in).
Overall, the acorn woodpecker is a stunning and unique bird that is sure to catch your eye and capture your heart with its striking appearance and distinctive call.
Distribution and habitat
The acorn woodpecker is a bird species that thrives in forested areas, particularly those with oak trees. You can find these beautiful birds in the coastal regions and foothills of Oregon, California, and the southwestern United States. However, they can also be seen in Central America, all the way down to Colombia.
These birds are adaptable and can survive in a variety of habitats, but they tend to prefer regions with a more temperate climate. In the northern areas of their range, they may live at lower elevations, while in Central America, they usually reside at altitudes above 1,000 m (3,300 ft).
When it comes to nesting, acorn woodpeckers are quite resourceful. They excavate their nests in cavities found in dead trees or dead parts of living trees. It’s an interesting fact that they don’t always build new cavities for their nests, but often use the same ones year after year.
Overall, the acorn woodpecker is a fascinating bird that adapts well to a variety of habitats, but is most commonly found in oak forests in the western United States and Central America. Their unique nesting habits add to their appeal, making them a popular sight for bird enthusiasts.
Behaviour and ecology
Acorn woodpeckers are fascinating birds that display unique social behaviors. They prefer to live and breed in family groups of up to 15 individuals and are known as cooperative breeders. These family groups vary in composition, ranging from monogamous pairs to polygynandrous breeding collectives consisting of coalitions of up to eight males and four females, along with nonbreeding “helpers at the nest” that are offspring from prior breeding events.
In these groups, all breeder males, who are usually brothers or fathers and their sons, compete for matings with all breeder females, who are sisters or a mother and her daughter. These females lay their eggs communally in the same nest cavity, resulting in a cooperative polygamy behavior that is rare among birds. It is believed that the availability of acorn storage granaries is a key limited resource driving this cooperative behavior.
Breeding coalitions can consist of up to eight cobreeding males and up to four joint-nesting females, but most nests consist of only a single breeder female and one to three cobreeder males. Nests can also contain up to ten offspring helpers. Despite the high degree of relatedness among most group members, inbreeding is rare because reproductive vacancies are filled by unrelated birds from elsewhere.
In groups with more than one breeding female, these females put their eggs into a single nest cavity, and once all the females start to lay, they stop removing eggs. Multiple paternity and maternity are common within groups containing multiple cobreeders, but no extra-group paternity has been detected. Acorn woodpeckers are truly fascinating creatures with a remarkable social structure.
Food and feeding
The acorn woodpecker is a fascinating species with unique behaviors and adaptations that set it apart from other birds. Known for its reliance on acorns for food, these woodpeckers have developed specialized behaviors that enable them to thrive in their habitat.
One interesting fact is that the acorn woodpecker may nest in the fall to take advantage of the fall acorn crop, a behavior that is uncommon among birds. This is because acorns are such an important resource to California populations that they will go to great lengths to secure them. To store their precious food, acorn woodpeckers drill small holes in “granaries” or “storage trees,” which are usually dead branches, snags, utility poles, or wooden buildings. These storage holes are used year after year and can consist of thousands of holes, each filled by an acorn in the autumn.
Interestingly, the availability of acorn crops influences the composition of acorn woodpecker communities. In years with a poor acorn crop, there are more non-breeding adults per social unit, while in years with a significant increase in acorn production, there is a correlating decrease in non-breeding adults per unit.
Despite their reliance on acorns, acorn woodpeckers primarily feed on insects, sap, and fruit. They have adapted their feeding behaviors to include sallying from tree limbs to catch insects, eating fruit and seeds, and drilling holes to drink sap.
But collecting and storing acorns is a significant part of the acorn woodpecker’s life. The woodpeckers select an acorn that is just the right size and move it to a hole that they have drilled. As the acorn dries out, they move it to smaller holes, and granary maintenance becomes a crucial part of their daily routine. The acorns are also visible, so the birds must defend their granary against potential cache robbers such as Steller’s jays and western scrub-jays.
In tropical regions, the acorn woodpecker stores acorns in natural holes and cracks in bark instead of constructing a “granary tree.” If the acorn crop is poor, these woodpeckers will move to other areas over the winter in search of better resources.
Overall, the acorn woodpecker is a fascinating bird species with remarkable adaptations that enable it to thrive in its habitat.
Threats and status
Acorn woodpeckers, a fascinating bird species that plays an important role in their ecosystem, are facing several threats due to habitat loss and degradation. In urbanized areas, non-native species are competing for their nest cavities, posing a continuous threat to their survival.
To protect these birds and ensure their continued existence, it is essential to maintain functional ecosystems that provide them with all the resources they need. These include mature forests with oaks capable of producing large mast crops and suitable places for the woodpeckers to nest, roost, and store mast.
It is crucial to encourage residents to preserve mature oak and pine-oak stands of trees and provide dead limbs and snags for nesting, roosting, and granary sites to help maintain the acorn woodpecker’s population. By taking these conservation measures, we can help protect this unique bird species and maintain a healthy ecosystem.
Legend has it that Walter Lantz, the creator of the famous cartoon character Woody Woodpecker, was inspired by the acorn woodpecker’s call when he was coming up with the character’s unique sound. Meanwhile, Woody’s appearance was inspired by the pileated woodpecker, which boasts a distinctive crest on its head. Lantz’s decision to combine these two woodpecker species to create one of the most recognizable cartoon characters in history is a testament to the enduring appeal and fascination that these birds hold for people of all ages.