Hopping across pavements, perching on TV antennas, roosting on air-conditioners; these are the birds that city dwellers ignore except to complain about their noise and their droppings. In English, birdwatchers jokingly call them “trash birds” because they are too common to be interesting. Yet these unloved birds deserve a second look, as they are incredibly resilient creatures that can show us a lot about how animals adapt to human environments.
Cities are tough environments for most wildlife, but species that thrive in close proximity with humans are called “synanthropes”, derived from the ancient Greek words “syn”, meaning “together”, and “anthropos”, meaning “man”. In 2023, a team of biologists at the University of California, Los Angeles evaluated 3,768 birds across 137 cities worldwide to identify the characteristics that make birds good synanthropes. They found that successful urban adapters are smaller, nest in trees or on buildings (not on the ground), and are capable of flying longer distances. They are also less territorial, more social, and flexible in terms of habitat or diet. Some species lay large clutches of eggs, allowing them to reproduce quickly. Others are slower breeding but longer-lived, which is associated with higher intelligence.
According to Arthur Yu, Assistant Education Manager at the Hong Kong Bird Watching Society, an incredible 580 species of birds are found in Hong Kong, but only 20-something are common in urban areas. Though most attention understandably goes towards the rare species that migrate through Hong Kong every winter, it is still worth paying attention to common urban birds. Yu emphasizes that our next-door neighbours do not only include Auntie Chan across the hall, but also the wildlife that lives around us, and that taking the time to appreciate it benefits our own mental health. Rather than viewing cities as divorced from nature, we can understand them as their own type of ecosystem and work to make them more hospitable to a greater diversity of species, whether that is by reducing the use of pesticides in parks and gardens, or by sticking anti-collision film on windows to prevent birds from crashing into them. And in this urban ecosystem, even the most unappreciated species have interesting stories to tell. Here are a few of Hong Kong’s “trash birds”.
Eurasian tree sparrow singing on a TV aerial. Photo credit: City Unseen, 2025.
These brown fluffballs with dark cheek patches are Hong Kong’s most abundant urban bird. Since 2016, the Hong Kong Bird Watching Society has conducted an annual sparrow census. They made sparrows their target species precisely because they are so common. Everyone can recognize them, so anybody can participate in the citizen science project. They are also a useful indicator of ecosystem health because a population crash would mean that something was seriously wrong. Their population indeed fell from over 300,000 to around 250,000 between 2016 and 2019 for reasons that are still unclear, but has stabilized since.
The census also provides very clear data showing that sparrows like to live where humans do. The district with the highest density of sparrows is Sham Shui Po. They are most abundant in parks, residential areas, and villages, and are even more common in commercial and industrial areas than on agricultural land. They do not live in forests, shrubland, or upland grassland. When humans abandon a village, so do the sparrows.
It is likely that after the decline of rice farming in Hong Kong, sparrows left the fields to forage in urban parks for grass seeds, insects, and scraps of human food. They probably build their nests in the crevices of buildings more often than they do in trees. They have also adapted to urban living by singing at a higher pitch to be heard over the noise of traffic (which is something that many species of urban birds do). The vast majority of sparrows do not migrate, but there is one population that does—about 200 sparrows pass through Poi Toi Island every spring on their journey northwards, but nobody knows where they come from, or where they go.
Rock pigeons. Photo credit: City Unseen, 2025.
The rock pigeon, perhaps the least popular of urban birds, has been domesticated for thousands of years. They are considered feral animals rather, more akin to stray cats than to wildlife. In Hong Kong they are legally classed as poultry.
They originated in North Africa, Europe and Western Asia but have spread to every continent except Antarctica. Their wild ancestors nested on cliff faces, which makes them particularly well-suited to breeding on building ledges. As a result of this evolutionary history, pigeons build incredibly flimsy nests—all they need is a loose circle of twigs to prevent their eggs from rolling off the edge. Rock pigeons must have been introduced to Hong Kong centuries ago, and up to the 1980s were commonly kept for food or racing.
A pigeon nest. Photo credit: Ludek, 2006, Wikimedia Commons, CC-BY-SA-3.0.
In 1987, the government placed limits on the number of poultry that could be kept in urban areas in order to control water pollution. In 1993, the Hong Kong Racing Pigeon Association went to court, arguing that racing pigeons were not poultry. They lost the case. The Court of Appeal ruled that the law was unambiguous, and that all domestic pigeons were indeed poultry. This is why when the government banned feeding pigeons in 2024, they had to amend the Wild Animals Protection Ordinance specifically to include pigeons. The older version already prohibited the feeding of wildlife at locations specified by the Agriculture, Fisheries and Conservation Department (AFCD), but pigeons were not legally wildlife.
Urban poultry keeping was banned entirely after the avian flu outbreaks of the late 1990s, but contrary to public perception, rock pigeons are not a significant carrier of avian flu, and in fact are fairly resistant to it. They can carry other diseases like cryptococcosis, histoplasmosis and psittacosis, but you are very unlikely to catch them unless you are immuno-compromised and somehow inhale large amounts of dust from their droppings. According to Yu, the main issues are the hygiene problems and overpopulation caused by people feeding them. If left alone, they are a fairly harmless presence.
Though often found in close proximity with rock pigeons, the spotted dove is a different, native species of wild pigeon, identifiable by its black and white spotted collar. Photo credit: City Unseen, 2025
A black kite soaring past a residential tower in Ma On Shan. Photo credit: Lee See-ming, 2013, CC BY-NC 2.0.
The black kite, which is often seen gliding between high-rises and over Victoria Harbour, is Hong Kong’s most common bird of prey. In fact, Hong Kong has possibly the highest concentration of black kites in the world. About 200 stay in Hong Kong over the summer, but in winter, a migratory population flies in from their breeding grounds in Russia and northern China, bringing their numbers up to 1,500-2,000. Hundreds roost together at night at Magazine Gap, Stonecutter’s Island, and Yeung Chau in Sai Kung.
Their diet makes them particularly adaptable to urban environments. While they do catch insects, rodents, and smaller birds including pigeons, they eat mostly dead things, which fulfils an important ecological role in recycling nutrients. They are often seen swooping down to grab dead fish out of the harbour. However, they will also pick up floating rubbish and circle above landfills in large groups.
Black kites line their nests with scraps of plastic bag, gloves, towels, and even paper offerings from cemeteries, a behaviour which puts them at risk as their legs get tangled up in plastic waste such as the strings of disposable masks. This is just one example of how human activity can threaten them despite their adeptness at exploiting urban food sources. They were once found all over Taiwan, but declined dramatically in the 1980s due to the use of certain agricultural pesticides, which gave them secondary poisoning after eating the rodents and birds that were the real target. It was only after Taiwan’s government discouraged the use of these pesticides in the 2000s that their population began to recover. While kites are common in Hong Kong now, they may not always be.
A house crow. Photo credit: GerifalteDelSabana, 2018, Wikimedia Commons, CC-BY-SA-4.0.
With about 100 birds based mainly in Sham Shui Po and Kowloon City, the invasive house crow has not become a widespread “trash bird” only due to constant efforts by the AFCD. Unlike the native collared crow and large-billed crow which live in marshlands and woodlands, the house crow is an expert urban exploiter; it survives in a wide range of climates and eats just about anything. Their initial appearance in Kowloon West in the 1980s, where they often scavenged at the Cheung Sha Wan Wholesale Food Market, led experts to believe that they were accidentally introduced to Hong Kong by cargo ships. As their broad diet includes the eggs and chicks of other birds, they could pose a major threat to native wildlife if allowed to proliferate.
House crows come from the Indian subcontinent, but have spread to other parts of Asia, Africa, Europe, and the Persian Gulf, sometimes by deliberate introduction, and in other cases by hitchhiking on ships. In Singapore, where they have no natural predators, they multiplied from fewer than 4,000 in 1987 to 130,000 by 2004. There, they are considered a major pest and disease vector, regularly drawing complaints for attacking pedestrians in the course of defending their chicks.
While crows are disliked and considered a bad omen in Chinese culture, they are remarkably intelligent, with problem-solving abilities on par with great apes. In Japan, another crow species, the carrion crow, has been seen dropping nuts onto roads to be cracked open by passing cars. House crows can recognize themselves the mirror, something that human babies start do at about 18 months of age: when researchers put coloured stickers on their throats where they could only be seen in a mirror, they tried to scratch the stickers off with their claws.
This intelligence is what makes them so adaptable—and so hard to get rid of. They quickly learn to recognize traps and avoid fast-acting poisons. There is little public information about the AFCD’s recent control strategies, but older documents point to methods like destroying their nests and baiting them with anaesthetic-laced meat to capture and euthanise them. While it is necessary to cull them to prevent them from spreading out of control, it is not their fault that they are here. They are simply too skilled at living in the world that humans created.
Special thanks to Arthur Yu, Hong Kong Bird Watching Society.
Montague H.C. Neate-Clegg et al., “Traits shaping urban tolerance in birds differ around the world”, Current Biology, v.33 i.9, 8 May 2023.
Croucher Foundation, “Birds in the city”, 13 March 2021.
Ann W. Y. To, Caroline Dingle, and Sarah A. Collins, “Multiple constraints on urban bird communication: both abiotic and biotic noise shape songs in cities”, Behavioral Ecology (2021), v.21 i.5, pp.1042–1053.
Jiehua Yu, “Urbanization alters the geographic patterns of passerine plumage color in China” Landscape and Urban Planning, v.248, August 2024.
Hong Kong Birdwatching Society, “Hong Kong Sparrow Census 2023 reveals a stabilizing population”, 2023.
Hong Kong Birdwatching Society, “Eurasian Tree Sparrow Passer Montanus”, Avifauna of Hong Kong, 2 June 2025.
Tammy Yeung, “The decline of pigeon racing in Hong Kong”, Hong Kong Lawyer, May 2020.
Hong Kong Birdwatching Society “Domestic Pigeon Columbia livia”, Avifauna of Hong Kong, 2 June 2025.
Croucher Foundation, “Black Kites: The Adaptable Raptor”, 13 March 2021.
Hong Kong Birdwatching Society, “Black Kite Milvus migrans”, Avifauna of Hong Kong, 10 January 2024.
Staff reporter, “Where eagles nest”, Young Post, 13 January 2011.
Lin Hui-Shan and Hong Shiao-Yu, “Conservation Action Plan for Black Kites 2019”, Forestry Bureau,
Agricultural Committee of the Executive Yuan, Taipei, Taiwan.
Hong Kong Birdwatching Society, “House Crow Corvus splendens”, Avifauna of Hong Kong, 7 June 2025.
Hong Kong Birdwatching Society, “House crows in Hong Kong: The beginning of an ecological catastrophe?”, PowerPoint presentation, 7 August 2004.
Koh Wan Ting, “Better ways to control crow numbers than culling them, says ACRES after Bishan crow attacks”, Channel News Asia, 22 February 2023.
Kanami Ara and Katsura Mikami, “Nut-cracking behaviour, by means of automobiles, by Carrion Crows in Hakodate City”, Japanese Journal of Ornithology, v. 68 i.1, pp.43-51, April 2019.
Amaan Buniyaadi, S. K. Tahajjul Taufique & Vinod Kumar, “Self-recognition in corvids: evidence from the mirror-mark test in Indian house crows (Corvus splendens)”, Journal of Ornithology, v.161 pp.341–350, 2020.
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