Introduction
An intergrade flicker is a hybrid bird that is a mix between two subspecies of the Northern Flicker woodpecker – the Yellow-shafted Flicker and the Red-shafted Flicker. The Northern Flicker itself has two distinct subspecies that live in different geographical regions and have slightly different physical features. However, in areas where their ranges overlap, intergrade flickers can occur as the two subspecies interbreed.
Intergrade flickers exhibit features that are a mix of their parent subspecies. This includes variations in the color of their wing and tail feathers, as well as the color of the feather shafts. An intergrade may lean more towards one subspecies or have a relatively even mix of traits from both. The prevalence of intergrades in certain areas can provide insight into the degree of intermingling and hybridization between the two Northern Flicker subspecies.
What are the two Northern Flicker subspecies?
The two main subspecies of the Northern Flicker are:
– Yellow-shafted Flicker (Colaptes auratus auratus) – This subspecies is found broadly across the eastern parts of North America. They are named for the yellow coloration of their wing and tail feather shafts.
– Red-shafted Flicker (Colaptes auratus cafer) – This subspecies inhabits the western portion of North America. As their name indicates, their wing and tail feather shafts are reddish in color.
The Yellow-shafted and Red-shafted Flickers occupy separate geographical ranges across most of the continent. However, these ranges overlap across a broad swath of the central and plains states. It is within this hybrid zone that intergrade populations occur.
Key physical differences between the subspecies
In addition to the shaft color, there are some other physical differences between Yellow-shafted and Red-shafted Flickers:
Feature | Yellow-shafted Flicker | Red-shafted Flicker |
---|---|---|
Plumage on underside of wings and tail | Yellow | Salmon-red |
Color of nape (back of neck) | Gray | Red |
Throat color (males) | Gray or grayish-brown | Red |
Face markings | Black crescent | Red or orange mustache |
What are some key features of intergrade flickers?
Intergrade flickers display an intermediate mix of traits between the two parent subspecies:
Plumage
– Wings and tail feathers can show a mix of yellow and red shafts
– Underside plumage mixes yellow and salmon-red feathers
– Throat may be partly red in males
– Nape can show variable gray and red patchwork
– Face markings are often an intermediate mix of a black crescent and faint red mustache
Size and shape
– No significant size differences compared to parent subspecies
– Bill shape and other structural features fall within the range of variation seen in pure Yellow-shafted and Red-shafted birds
Behavior
– Exhibits the full range of typical Northern Flicker behaviors
– Sings songs that blend characteristics of both parental forms
– No behavioral differences that can reliably distinguish intergrades from pure subspecies
What causes intergrade flickers?
Intergrade Northern Flickers occur due to interbreeding between the Yellow-shafted Flickers and Red-shafted Flickers within their hybrid zone. The two subspecies remain largely separate across most of the continent. But in areas where their breeding ranges abut one another, the opportunity arises for hybrid pairings to form and produce mixed offspring.
Some key factors that enable intergrade birds to occur are:
– Suitable habitat continuity between the ranges of the two subspecies
– Ongoing contact and mingling where the ranges intersect
– Lack of strong barriers to discourage interbreeding
– Continued gene flow between the subspecies where they meet
– Sufficient genetic compatibility for hybrid pairings to produce viable offspring
The broad hybrid zone between the two flickers provides ideal conditions for intergrades to occur across multiple generations. This hybrid mixing is what gives rise to birds that express a blend of parental traits in varying combinations.
Where are intergrade flickers most commonly found?
Intergrade Northern Flickers are most prevalent in areas where the breeding ranges of the Yellow-shafted Flicker and Red-shafted Flicker abut and overlap. This primarily includes a broad swath of central and western states:
States with extensive intergrade populations
– Texas
– Oklahoma
– Kansas
– Nebraska
– South Dakota
– North Dakota
– Montana
– Wyoming
– Colorado
– New Mexico
Intergrade birds can also be found less commonly along the bordering regions of the parental ranges further east and west. But the highest density of intergrades occurs within the core hybrid zone spanning the Great Plains and western states listed above. The prevalence gradually decreases moving away from this central zone.
What is the conservation status of intergrade flickers?
Intergrade Northern Flickers are not considered a distinct species or subspecies. They are simply hybrids between the two recognized subspecies – Yellow-shafted Flickers and Red-shafted Flickers. As such, intergrades are not assigned their own conservation status.
However, some ornithologists believe intergrade populations are a significant component of the Northern Flicker’s genetic variation and should be conserved. Rather than being an anomaly, they represent an important process of gene flow between the subspecies where their ranges intersect.
Overall, the Northern Flicker remains a widespread and common species across North America. They are classified as Least Concern on the IUCN Red List with stable overall populations. Any conservation efforts for flickers should consider maintaining suitable habitat within the hybrid zone, where intergrade birds occur.
How can you identify an intergrade flicker?
Telling an intergrade Northern Flicker apart from a pure subspecies bird can be tricky. Look for the following key features:
Plumage
– A mix of yellow and salmon-red on the undersides of wings/tail
– Both gray and red patches on the nape
– A blend of a black crescent and faint red mustache on the face
– Wing/tail shafts showing an intermediate range of yellowish-red
Distribution
– Found within the Central/Great Plains hybrid zone where ranges overlap
Song
– Contains a mix of characteristics from both Yellow-shafted and Red-shafted songs
Behavior
– Exhibits full range of normal Northern Flicker behaviors
– No behavioral differences from pure subspecies birds
Look for a balance of features rather than matching strongly to either parental subspecies. The more even the mix, the more likely the bird is a classic intergrade. Subtle plumage mixes can occur in pure birds, so be cautious claiming an intergrade from minimal hints alone.
What is the genetic basis for intergrade flickers?
The genetic basis underlying intergrade Northern Flickers relates to the level of divergence and compatibility between the two subspecies. Some key genetic factors are:
Incomplete reproductive isolation
– The two subspecies remain close enough genetically to interbreed successfully
Limited hybrid fitness barriers
– Hybrid pairings and offspring are viable and fertile
– No strong intrinsic genetic barriers to gene flow between the subspecies
Polygenic trait inheritance
– The intergrade mix of parental traits is controlled by multiple genes
– Offspring show continuous range of variation in proportions of each subspecies’ genes
Maintenance of genetic variability
– Continued backcrossing into parental types ensures rich gene flow
– Prevents fixation of hybrid genes into a uniform intermediate
The level of divergence between Yellow-shafted and Red-shafted Flickers allows hybridization while maintaining each subspecies’ integrity across most of their respective ranges. Intergrades represent an important natural geneflow mechanism for the species as a whole.
How common are intergrade flickers relative to the pure subspecies?
The prevalence of intergrade Northern Flickers compared to pure subspecies birds varies across different parts of the hybrid zone:
Central hybrid zone
– Roughly 25-50% of birds are intergrades
– Equal mix of pure Yellow-shafted, pure Red-shafted, and hybrids
Eastern periphery
– 10-20% intergrades, 80-90% pure Yellow-shafted Flickers
Western periphery
– 10-20% intergrades, 80-90% pure Red-shafted
Outside hybrid zone
– Less than 5% intergrades, 95%+ pure parental types
The core areas of range overlap contain the highest proportion of intergrades. Their prevalence drops off towards the edges as each subspecies becomes dominant. But some intermixing can occur across the broad contact zone.
Do intergrade and pure flickers intermingle and interbreed?
Within the hybrid zone, intergrade Northern Flickers form mixed flocks and breed freely with pure subspecies birds. Some key patterns seen are:
Flocking
– Intergrades, Yellow-shafted Flickers, and Red-shafted Flickers all forage together
– No segregation based on genetic background
Pairing and mating
– Intergrades can mate with either parental subspecies
– Hybrid-hybrid pairs also occur frequently
Site fidelity and migrations
– All birds remain intermixed when breeding or migrating
– No separation of intergrades and pure subspecies
Complete integration and ongoing gene flow helps maintain the intergrade zone. The interbreeding maintains high variability in hybrid proportions across generations.
What impacts might climate change have on intergrade flickers?
Some potential impacts of climate change on intergrade Northern Flicker populations include:
Shift in subspecies ranges
– Altered suitable habitat could shift subspecies ranges
– May expand or contract the hybrid zone
Disruption of migratory patterns
– Changes in food availability could impact migration timing and routes
– Could alter mixing opportunities for subspecies
Habitat changes
– Flicker habitat like open woodlands may be affected by climate shifts
– Loss of nesting, roosting, and foraging sites
Phenological impacts
– Shift in timing between food availability and breeding seasons
– Could impact breeding success and fitness
Extreme weather
– Increased droughts, storms, etc may threaten populations
Ongoing monitoring of flicker subspecies distributions and intergrade prevalence will be needed. Conservation approaches may need to adapt to maintain sufficient habitat connectivity to support intergrades within a shifting hybrid zone.
What are some key takeaways about intergrade flickers?
Some key points to summarize intergrade Northern Flickers:
– Hybrids between the Yellow-shafted and Red-shafted subspecies
– Mix parental traits in varying degrees based on polygenic inheritance
– Most prevalent in the central hybrid zone between subspecies ranges
– Represent an important natural geneflow mechanism
– Intermix and interbreed freely with pure parental types
– Not a distinct taxonomic group but still important to conservation
– Climate change may impact distribution and integrity of hybrid zone
– Identification relies on intermediate mix of diagnostic traits and distribution
Intergrades illustrate the dynamic nature of divergence and speciation. Their study can reveal important insights into adaptation, gene flow, and the genesis of biodiversity.