Pigeons are an ubiquitous sight in cities today, and people tend to either love them or completely hate them. But they are semi-domesticated pigeons, very adapted to life with and close to humans. New research from the Department of Biology at the University of Oxford reports the discovery of a rare colony of their wild counterparts – Wild Rock Dove (columba livia) — on remote Scottish and Irish islands.
The discovery of these colonies is of major interest to researchers and ecologists. The species is virtually extinct in England and Wales today. Feral pigeons, on the other hand, carry an important genetic component of domestic doves. Together, these two factors make it nearly impossible for researchers to obtain genetic material from true, unhybridized wild doves in order to study the evolutionary history of the species.
For other species, this research highlights the role of hybridization processes in the extinction of species.
Pigeon in the coal mine
“Wild pigeons are particularly important because the species is one of the animals with the closest relationship to humans,” says William J. Smith, a graduate student in Oxford University’s Department of Zoology and author. corresponding to the article, for ZME Science. “As one of the first domesticated birds, throughout history we have relied on them for food, navigation, messaging and science (they [also] appear massively in mythology and religions).
“In particular – in science – we use domestic pigeons as model organisms to study genetics, behavior and urban evolution. Being able to study the non-domesticated form will help us establish how the traits we study in a laboratory/home environment evolved, and what their purpose is in nature.
Researchers led by members of Oxford University’s biology department have discovered rare colonies of wild ancestors of common domestic and feral pigeons.
Today’s feral pigeons, those that fly around our towns and villages, are descended from escaped domestic birds. These domestic birds, in turn, were bred from wild rock pigeons, whose habitat includes sea caves and mountain slopes across Africa, Asia and Europe.
Although feral pigeons are very successful, Rock Pigeons are experiencing a steady and significant decline in their range worldwide. But, although we know the species is struggling, researchers have had great difficulty in charting this decline reliably due to the high level of interbreeding – and subsequent replacement with – feral pigeons. Today, they only survive in very small, isolated populations that feral pigeons have not yet colonized. Many ornithologists believe that there may not be a wild rock pigeon.
Some potential areas where the species could persist include isolated sites in Europe, the Faroe Islands, some areas of the Mediterranean Sea, as well as sites in Scotland and Ireland.
“At the individual level, the differences between wild rock pigeons are minimal. The wild form has a thinner, longer bill and a more rounded forehead. Feral pigeons have a noticeably smaller “cere” which is a white spot on the top of the beak. The biggest differences are evident when you see a flock of birds,” says William Smith for ZME Science. “A flock of feral or hybrid pigeons will contain a mixture of different colors and plumage patterns (much like a group of domestic dogs of different breeds!), whereas a flock of rock pigeons consists of birds of look identical (more like a pack of wolves!), which is quite shocking when you’re used to seeing a motley crew of “normal” feral pigeons.
To determine if these sites are still home to wild rock pigeons, the team studied bird populations in Scotland and Ireland, at sites such as North Uist (Uibhist a Tuath) in the Outer Hebrides, Orkney and Cape Clear. Island. They examined their genetic make-up to determine if they were truly wild birds and to quantify the extent of the wild pigeons’ genetic influence in their genomes. Samples for the study – consisting of feathers – were collected through a combination of expeditions led by the team themselves and collaboration with bird banders from the British Trust for Ornithology
After sequencing the DNA of a large number of birds, the team was able to highlight the differences between wild pigeons and wild rock pigeons, and thus measure the level of interbreeding between the two in various populations of birds.
The results confirmed the existence of birds in the UK and Ireland that descend from an undomesticated line, the original line from which domestic and wild birds split. Despite this, different populations showed different levels of interbreeding. Orkney rock pigeons have had many crosses with feral pigeons and are in danger of hybridizing to the point of disappearing as a separate line. Those in the Outer Hebrides, on the other hand, remain almost immune to the influence of feral pigeons.
“We have identified feral pigeon ancestry in most Scottish and Irish dove populations we have sampled, and there have been feral pigeons in Europe for hundreds of years. It was therefore truly surprising to find that the Rock Doves of the Outer Hebrides showed negligible signs of hybridization,” William Smith explained in a press release.
“It’s important to remember that hybridization, to some extent, is part of nature. Gene flow between and within species can generate diversity that fuels evolution,” he adds for ZME Science. “On the other hand, human movement of animals and plants across the globe has led to an increase in this gene flow which can cause massive ‘homogenization’ at the genomic level, replacing locally adapted and rare forms with common or invasive parents This reduces overall biodiversity globally, which will reduce the ability of ecosystems to cope with changing conditions (e.g. climate change) Replacement of rock pigeons with feral pigeons (which are an animal superabundant) is an example of this process.
The results have direct value in showing us that wild doves still exist, albeit in numbers and in limited areas, in the wild. This will have important implications for species conservation efforts. In a broader context, it also teaches us valuable lessons about how best to preserve the genetic stock of wild species in other parts of the world. Finally, it deepens our understanding of how hybridization can contribute to causing a “hidden” extinction of certain species, slowly replacing it with wild or domesticated hybrids.
“While huge sums of money have been spent in Britain to conserve and study the wild cat, which is threatened with extinction through hybridization with feral domestic cats, rock doves have not been studied before despite an almost identical problem. This means that we have not understood their conservation status and value,” concludes William Smith.
“Now we are aware that the Outer Hebrides population, in particular, has experienced negligible gene flow with its invasive relative, the feral pigeon. We will be able to monitor this population to try and reduce this gene flow at the future and preserve undomesticated rock pigeons. In addition, more generally, the process of extinction through hybridization has caused significant loss of biodiversity across the world. For example, the Lesser Antillean iguana, the subspecies Seychellois Madagascan Dove and Scottish Wildcat have all experienced dramatic declines as a result of interbreeding with their more common relatives after humans introduced the latter into their ecosystem.Our Rock Dove study will contribute to the body of knowledge on this phenomenon, which is of interest to conservation biologists around the world.
The article “Limited domestic introgression in a definitive refuge of the feral pigeon” was published in the review iScience.