Mallard ducks (Anas platyrhynchos) exhibit striking variations in plumage coloration and patterning. The familiar green-headed Mallard drake is instantly recognizable. However, female Mallards have a rather drab mottled brown plumage. But even among male Mallards, there is variability in coloration. So why do Mallard ducks come in different colors? The key factors are genetics, breeding strategy, and sexual selection.
Genetics Of Plumage Coloration
The genetic mechanisms controlling Mallard plumage coloration are complex. As with many birds, Mallard plumage color is strongly influenced by melanins. There are two main types of melanin: eumelanin which produces black, brown, and gray colors, and phaeomelanin which produces reddish-brown hues. The specific combination and concentration of these melanins produces the array of natural plumage colors.
Several genes interact to control the type, amount, and pattern of melanin deposition in developing feathers. A key locus is the MC1R gene which codes for the melanocortin-1 receptor protein. Variants of the MC1R gene result in differential expression of eumelanin and phaeomelanin. Additional genes modify this pathway, leading to intricate combos of melanin hues.
Drake Plumage Patterns
In Mallard drakes, plumage patterns are controlled by the interplay of multiple genes. The characteristic green head of drakes results from a low density of melanins. The chestnut breast occurs from phaeomelanin expression. Meanwhile, the gray body feathers are created by eumelanin. Modifier genes control the boundaries between color regions.
| Body Region | Main Pigment |
| Head | Low melanin density |
| Breast | Phaeomelanin |
| Belly | Eumelanin |
There are also white-colored morphs of Mallard drakes (“albino Mallards”). These result from inherited mutations causing a complete lack of melanin production. Overall, the color diversity seen among male Mallards is facilitated by the interplay of multiple genes and alleles modulating melanin type and density across feather regions.
Female Plumage Patterns
In contrast to the colorful male, female Mallard plumage is cryptically-colored for camouflage. The mottled patterns aid in concealment from predators during nesting and brood-rearing. The genetic basis is centered around increased melanin density compared to males.
There are three characteristic color morphs in females:
– Mottled brown – the predominant pattern with buff, brown, and black mottling
– Mallard-like – similar patterning to male albeit at lower color saturation
– Dark morph – increased eumelanin produces darker brown plumage
As in males, these morphs are controlled by variants in MC1R and modifier genes. But higher baseline melanism dampens expression of bright colors. There are also various rarer female morphs including “albino” and melanistic black. Overall, female Mallard plumage is fine-tuned for camouflage via genetic pathways modulating melanin deposition.
Breeding Strategies
A key reason for the divergence in coloration between male and female Mallards relates to their breeding ecology. Mallards form short-term pair bonds each breeding season, but extra-pair matings are frequent.
Up to 13% of Mallard broods can be sired by a male other than the paired mate. Mallard drakes do not contribute to rearing offspring. Their bright “secondary sexual” plumage instead functions to attract mates and intimidate rival males during the competitive breeding season.
Meanwhile, the female’s cryptic plumage promotes concealment while incubating eggs and raising ducklings. These complementary reproductive strategies reinforce distinct selection pressures on male versus female plumage traits.
Sexual Selection
Sexual selection also drives the evolution of elaborate colors and patterns in male Mallards. Females demonstrate preferences for specific male traits during mate selection. Mallard drakes with the brightest plumage tend to achieve greater reproductive success.
Several lines of evidence indicate Mallard females preferentially mate with more colorful males:
| Study | Main Finding |
| Omland 1996 | Females mated more with males with brighter bills |
| Stibor 2006 | Females preferred males with greater UV reflectance |
| Butler 2007 | Females chose males with brighter plumage |
Sexual selection continually favors the most visually-striking male phenotypes. This process likely accounts for the elaborate ornamentation and vivid colors exhibited by Mallard drakes compared to females.
Variation Across Range
Interestingly, Mallard coloration is not uniform across their worldwide distribution. Compared to the classic green-headed American Mallard, European Mallards tend to have a yellow bill and purplish speculum instead of blue. Mallards in Asia and New Zealand exhibit a white throat and face instead of the green head.
These geographic tweaks to the core Mallard plumage likely reflect local sexual preferences and environmental pressures. Migration and hybridization also stir up new combinations of ancestral color variants. Mallards demonstrate a surprising fluidity in plumage traits over their broad natural range.
Hybridization Effects
Interbreeding with related duck species also introduces new plumage varieties into Mallard populations. Mallards frequently hybridize with other ducks across the Northern Hemisphere. Hybrid offspring can manifest unique mixes of parental plumage traits.
Some important examples of wild Mallard hybrids include:
| Hybrid Common Name | Parent Species |
| Brewer’s Duck | Mallard x Gadwall |
| Mottled Duck | Mallard x American Black Duck |
| Hawaiian Duck | Mallard x Grey Duck |
Via hybridization, Mallards gain new plumage genes and variants. This enhances color variability in Mallards – especially in regions where they co-occur with other duck species.
Domestic Mallard Varieties
The diversity of Mallard plumage coloration and patterning is exemplified by domestic Mallard breeds. Mallards have been domesticated as poultry for centuries. Artificial selection by duck breeders has yielded a plethora of unique plumage types.
Some examples of bred domestic Mallard varieties include:
| Breed Name | Plumage Features |
| Aylesbury | White feathers |
| Cayuga | Black with green iridescence |
| Rouen | Wild-type Mallard colors |
| Swedish Blue | Solid grey-blue |
Domestication has uncovered and fixed a palette of latent color variants hidden in the Mallard genome. It highlights the extent of underlying plumage diversity supported by Mallard genetics.
Conclusion
In summary, several key factors underlie the diversity of color patterns observed in Mallards:
– Genetic control of melanin types allows complex combinations of hues
– Separate selection on male and female plumage suits their differing reproductive strategies
– Sexual selection drives ornamentation and bright colors in males
– Hybridization introduces new plumage traits and alleles
– Domestication elucidates a range of innate color varieties
Mallard plumage coloration exemplifies the multidimensional influences of genetics, ecology, behavior, and evolution in generating avian diversity. Their striking intersexual differences in coloration have long fascinated biologists and ornithologists. Continued research will likely reveal deeper insights into both the mechanism and function of variable color patterning in this ubiquitous duck species.
