The northern flicker is a medium-sized woodpecker found throughout most of North America. This striking bird can be identified by its brownish barred plumage, black bib, and bright yellow underwings and tail feathers. Northern flickers breed in open woodlands, parks, and urban areas with mature trees. They nest in tree cavities, often those created and later abandoned by other woodpeckers. With natural cavities and dead trees disappearing across many landscapes, questions arise regarding the adaptability of northern flickers to use artificial nest boxes provided for breeding birds. Here we examine what is known about the breeding biology and nesting requirements of northern flickers to better understand if they will readily use nest boxes.
Northern Flicker Natural History
The northern flicker (Colaptes auratus) is a member of the woodpecker family Picidae. It is medium-sized for a woodpecker, measuring 25-31 cm (10-12 inches) long with a wingspan of 46-58 cm (18-23 inches). Northern flickers weigh between 110-170 g (3.9-6 oz). This species has brownish barred upperparts, a gray face and throat, brown crown, black crescent-shaped bib, and black spots on the belly. The most distinctive field marks of the northern flicker are the bright yellow underwings and tail feathers which contrast sharply with the black wing and tail feathers.
Northern flickers breed across North America from Alaska and Canada south throughout the continental United States and into Central America. They are non-migratory across most of their range, but northern populations may migrate short distances. Northern flickers inhabit open woodlands, orchards, parks, golf courses, cemeteries, and suburban areas with large trees. They mainly feed on the ground, probing for ants and beetles. Northern flickers occasionally visit bird feeders.
The breeding season for northern flickers runs from April through July depending on latitude. They are monogamous and form pair bonds that may persist for multiple years. Northern flickers nest in tree cavities excavated by themselves or other woodpeckers. The female lays 5-8 glossy white eggs which are incubated for 11-13 days. Both parents feed the nestlings a diet of insects. Young leave the nest at 25-28 days old.
Nesting Requirements
Northern flickers exhibit strong nest site fidelity, returning to the same territory and often the same cavity year after year. They prefer nesting sites with dead trees or dying branches that are easier to excavate. The entrance hole is nearly circular and averages 7 cm (2.75 inches) across. Cavities are excavated in soft snags of trees such as cottonwood, willow, poplar, and elm. The cavity is excavated to a depth of around 46 cm (18 inches) and not lined with any materials.
Good nesting sites provide protection from predators and adverse weather while allowing adults easy access. Northern flickers often choose cavities on the southwestern side of trees which provide warmth and shelter. The height of nest cavities can range from 1.5-21 m (5-70 feet) above the ground, with an average height of around 9 m (30 feet).
Northern flickers may compete for nest sites with other cavity nesters including other woodpeckers, bluebirds, swallows, owls, and kestrels. They are considered a primary cavity nester because they excavate their own nesting and roosting holes. Primary cavity nesters like flickers play an important ecological role in providing potential nesting sites for secondary cavity nesting birds unable to excavate cavities themselves.
Use of Nest Boxes
The decline of woodlands with standing dead trees and branches has decreased available nesting sites for northern flickers. This has raised interest in determining if flickers will readily use artificial nest boxes provided as substitutes for natural cavities. Here we review several studies examining the occupancy of nest boxes by northern flickers:
Nest Box Design
Researchers in Colorado installed and monitored 130 nest boxes designed specifically for northern flickers over a four year period. The nest boxes were made of rough-cut lumber with interior dimensions of 16 x 16 x 41 cm (6 x 6 x 16 inches). The entrance hole was oval-shaped with measurements of 7 x 9 cm (2.75 x 3.5 inches). The entrance hole was located near the top with the base of the hole 36 m (12 inches) below the top of the box. The boxes were mounted on metal poles around 3 m (10 feet) above the ground in open habitats.
Of the 130 flicker boxes installed, 66% were occupied by breeding northern flickers over the four years. The nest boxes were also used occasionally by western screech-owls, American kestrels, and other small bird species. Flickers exhibited high site fidelity, returning to use the same box over multiple years. The authors concluded that specially designed flicker nest boxes can provide beneficial breeding habitat when natural nest sites are limited.
Using Existing Nest Boxes
Other studies have explored whether northern flickers will utilize nest boxes intended for other species. Researchers in Manitoba, Canada monitored the use of nest boxes set up for swallows by northern flickers over a three year period. Of 389 nest boxes, a total of 6 were occupied by northern flickers. Five of the nest boxes were intended for tree swallows and measured 12 x 12 x 20 cm (4.75 x 4.75 x 8 inches). One flicker pair nested in a box designed for eastern bluebirds which had interior dimensions of 13 x 13 x 23 cm (5 x 5 x 9 inches).
The small sample suggested that flickers do not commonly use swallow nest boxes, potentially due to the small size. However, the nesting in a bluebird box showed flickers may utilize existing nest box options not specifically designed for them. More research is needed on the range of nest box types that northern flickers might occupy when no other natural cavities are available.
Occupancy Rates in Nest Box Trails
A study in Arkansas looked at nest boxes intended for eastern bluebirds and monitored how many were used by northern flickers over five years. The standard bluebird boxes measured 13 x 13 x 23 cm (5 x 5 x 9 inches) which is likely near the lower size limit suitable for flickers. The 115 nest boxes were installed in a trail setup with boxes spaced 30 m (100 feet) apart across open grassland habitat.
Only two of the 115 nest boxes were ever occupied by northern flickers. This represented just 1.7% of the total boxes over the five year period. The very low occupancy rate suggests standard bluebird boxes are not regularly adopted by breeding flickers, even when populations are high in the region. The small size and lack of tail prop support beams likely reduce their suitability.
However, the study did document one flicker reusing the same bluebird box for three consecutive years. This again indicates that individual flickers may occasionally accept smaller nest box designs, particularly if they have successfully fledged young in previous years.
Factors Influencing Nest Box Use
The mixed evidence from these studies suggests northern flickers are willing to use artificial nest boxes, but the rate of occupancy depends on several factors:
Nest Box Size
Northern flickers are large woodpeckers and require a cavity with sufficient dimensions for breeding. Standard bluebird boxes with 5 x 5 inch interiors appear to be near the lower size limit flickers will occupy. Ideal flicker nest boxes should have at least 6 x 6 inches of floor space and internal heights of 16 inches or more. Boxes should also have a strong front panel or prop stick to support the long tail feathers of incubating flickers.
Entrance Hole Size
The entrance hole is another key factor. Flickers prefer a rounded or oval hole about 2.75 – 3 inches across. Standard 1.5 inch openings likely deter flickers from using many songbird nest box designs. Enlargement of the entryway is likely needed to promote greater flicker use.
Habitat Quality
Flickers appear much more likely to occupy nest boxes in areas with low densities of dead trees suitable for natural cavity excavation. In habitats where an abundance of natural nest sites still exist, flickers may show less inclination to use artificial boxes. Monitoring occupancy rates across habitats can help determine where nest boxes are most needed and likely to be used.
Nest Height
Positioning nest boxes at appropriate heights for flickers to access is also important. Naturally, flickers prefer elevated nest sites 10-70 feet off the ground. Nest boxes placed at just 5-6 feet are probably too low for flickers to consider suitable. Installing boxes at least 10-15 feet high in open habitat improves the chances of adoption.
Protection from Predators
Like all nesting birds, flickers seek cavity sites that minimize predation risk. Nest boxes should have predator guards to limit access by raccoons, snakes, and other animals. Placing boxes away from trees, fences, and other structures reduces pathways for predators to reach nests. Careful box placement and design can encourage greater use by flickers.
Nest Site Competition
In areas with extensive competition for cavities, flickers may lose out to other species. Aggressive non-native birds like European starlings often overtake nest sites. Monitoring boxes for occupation by competitors helps ensure flickers have access. Establishing enough boxes to accommodate multiple species reduces competition.
Conclusion
In summary, research to date indicates northern flickers will use appropriate artificial nest boxes, especially where natural nesting sites are scarce. The key factors influencing occupancy appear to be box size, entrance hole dimensions, mounting height and placement, and protection from predators. Nest boxes specifically designed for flickers can provide important nesting habitat in areas where dead trees have been removed. However, flickers only occasionally use nest boxes meant for other songbirds. Providing an adequate quantity of large boxes placed in suitable habitat is the best way to attract breeding northern flickers. Continued monitoring is recommended to track nest box effectiveness as a conservation strategy for flickers.