Black-headed seagulls (Chroicocephalus ridibundus) are a relatively common species of gull found across much of Europe and Asia. However, like many animals, color variations can occur in certain individuals within a species. The black-headed seagull typically has a black head in the breeding season, with a white body and gray wings. A black-headed seagull with an entirely black plumage is extremely rare. In this article, we will examine how rare the black variant of the black-headed seagull is and look at some possible reasons for this rare color morph.
How Rare Are All Black Black-Headed Seagulls?
Black-headed seagulls with an entirely black plumage are very rare. In fact, only a handful of sightings have ever been reported. In May 2012, an entirely black black-headed seagull was spotted and photographed on Gugh, an island in the Isles of Scilly in the UK. This sighting generated a lot of interest from birdwatchers as it was potentially the first documented sighting of an all black black-headed seagull in the UK.
Another sighting occurred in April 2013 in Dorset in southwest England. The gull was seen among a colony of normal looking black-headed gulls and stood out dramatically due to its uniformly black plumage. The observer, a bird ringer named John Underhill-Day, estimated that this black seagull was one in approximately 750,000 normal black-headed seagulls. This provides an idea of just how exceptionally rare these black variant birds are.
There have been a couple other documented sightings of all black black-headed seagulls in European countries like the Netherlands and Spain. However, overall there are only a handful of accepted records across Europe and Asia. Given the species’ large population and distribution, which is estimated to be between 19,000,000 – 44,000,000 mature individuals, entirely black variants are exceptionally rare. The frequency is often estimated to be 1 in a million or less.
Partial Leucistic Birds Are More Common
While entirely black black-headed seagulls are incredibly rare, partial leucistic birds exhibit some white plumage still occur more frequently, though still uncommon. Leucism is a condition caused by a genetic mutation that prevents pigment cells from coloring some or all of a bird’s plumage. It differs from the total lack of melanin pigment known as albinism.
There are more regular sightings of black-headed seagulls with a mix of black and white feathers reported. These leucistic gulls display a higher percentage of white plumage than the normal species, but still have some black feathers in patches or across parts of their bodies. These partially leucistic birds are more common than the extremely rare totally black variant. However, they are still unusual and of interest to birdwatchers when spotted in the field. The variance in plumage patterns is quite high in leucistic gulls.
Reasons For Rare All Black Plumage
So what makes the all black morph of the black-headed seagull so exceptionally rare? There are a few possible explanations:
Genetics
The genes responsible for an entirely black plumage in this species are very rare. The specific combination and mutations of genes required to produce all black coloring across the entire body only occurs in a tiny fraction of birds. To have no white feathers at all is highly genetically unlikely. Most black morphs retain some white feathers or patches of white due to the genetics involved.
Lack of Camouflage
The all white head and body of the black-headed seagull serves as effective camouflage in its coastal cliff breeding habitat. An all black bird would stand out starkly against light backgrounds, making them vulnerable to predation. This lack of camouflage and survival disadvantage likely removes all black gulls from the population quickly through predation.
Melanin Overproduction
The melanin pigment that controls coloration may be overproduced in rare cases, turning more feathers black than normal. However, it is unlikely that melanin production could be so ramped up that it covers every single feather. Some intervening white feathers almost always occur. Complete melanin overproduction across all feathers simultaneously would be highly unusual.
Dietary Factors
Some pigment changes can be influenced by dietary factors. However, it would be difficult to explain how diet could eliminate all white feathers by making every single one fully black. Diet may play a small role but is unlikely to produce an all black plumage alone. Some white feathers would remain.
Sightings of All Black Seagulls Are Important to Science
The extremely rare sightings of totally black black-headed seagulls provide valuable data for ornithology and bird genetics. When these unique birds are sighted, it presents an important opportunity for scientists to study them and gain insights into plumage morphs. Photographs and documentation of any all black seagulls allows researchers to analyze the genetics, morphology and other factors influencing this ultra-rare variant.
If you are lucky enough to spot an entirely black black-headed seagull in the field, it is a significant find. Make sure to meticulously document the sighting and notify local ornithological organizations. Your sighting will make an important contribution to continuing research on bird genetics and plumage variation.
Scientists can also learn more about the evolution of melanin mutations by comparing the ultra-rare all black individuals to more common partial leucistic morphs. Careful study and genetic analysis of these birds helps explain the variability in gull coloration overall.
Conclusions
In summary, black-headed seagulls with completely black plumage are extraordinarily rare, with only a smattering of accepted sightings across Europe and Asia. The frequency is often estimated to be 1 in a million or less within the overall population. A combination of genetic improbability, lack of camouflage, and difficulties producing total melanin saturation across all feathers likely explains the scarcity.
Partially leucistic black-headed seagulls with a mix of black and white feathers are seen somewhat more regularly. However, the all black morph remains incredibly unusual. Its extreme rarity makes any sightings scientifically valuable as data points for research. Careful documentation of any all black seagulls allows ongoing study into plumage genetics and evolution. So if you are ever fortunate enough to spot one of these unique black birds in the wild, be sure to take detailed notes and photographs for ornithology!
