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Nestled between the hills north of Hong Kong and the breathtaking skyline of Shenzhen lies Deep Bay, semi-encircled by the Ramsar site of Mai Po wetland, a location of significant ecological interest home to numerous species of birds.  

Since the opening of China’s economy in the 1990s, Shenzhen has grown exponentially into a city of almost 13 million people. Deep Bay faces severe environmental threats including water pollution, rising mudflat levels from intense urbanisation and land reclamation on the Shenzhen side of the Bay. Mangrove forests have been cut down and the natural coastline converted into concrete sea walls. But threats to the natural order extend to the sky. The high-rise buildings in Shenzhen Bay are threatening the bird populations that find sanctuary at the Mai Po wetland during the winter season.

Mai Po Bird Species

Every winter, around 90,000 migratory birds seek refuge in the marshes and mudflats of the internationally-acclaimed Mai Po Nature Reserve in Hong Kong. Of the 380 species of birds that inhabit the reserve, 35 are of global conservation concern, including the Saunders’s gull and the black-faced spoonbill. 

Other critters such as otters, fiddler crabs and mudskippers also call the area home, and are the main food source of the waterbird. Hong Kong is situated beneath two major bird migratory pathways, the East Asian-Australasian Flyway and the West Pacific Flyway. Birds with breeding sites in North Asia and Siberia fly to Hong Kong every winter to rest and stay over winter and they fly back to their breeding site in spring. The nature reserve is managed by World Wildlife Fund (WWF) and a bird survey is conducted every winter by the Bird Watching Society (BWS). 

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Figure 1. Number of overwinter waterbirds surveyed by the Bird Watching Society

A clear correlation exists between the construction boom that has engulfed Shenzhen and declining bird populations. In particular,  the 2019 BWS annual report shows that the number of birds has decreased since 2008, coinciding with the development of Nanshan and Futian districts in the west and north of Shenzhen Bay, adjacent to the Mai Po Nature Reserve. 

Overall Shenzhen, one of China’s premier shipping and manufacturing centres, is home to 223 completed skyscrapers higher than 150m, giving the city the dubious honour of having the third largest concentration of such infrastructure in the world, after neighbouring Hong Kong and New York City. 

Shenzhen’s construction boom is impressive. In 2008 alone, eight skyscrapers taller than 150m were completed and in 2017 the fourth tallest skyscraper in the world- the Ping An Finance Centre- was completed, standing at 599m tall. More skyscrapers are scheduled for construction, including China’s would-be tallest skyscraper. At 700m tall, the project is expected to be completed by 2023. But the concrete jungle represents a major flight hazard for migratory birds.

How many birds are killed by skyscrapers?

Bird-skyscraper collisions are decimating populations. This phenomenon is known as towerkill; the dynamics of which have been studied in Toronto and New York City. It is estimated that nine million birds die each year due to them mistaking reflective windows for open sky or being dazzled by the bright lights from the skyscrapers at night. 

There are no official studies of towerkill in China but it is estimated that the number of birds killed would be much higher than New York City as the skyscrapers in Shenzhen are more concentrated and the urban area is in close proximity to the wetland that the birds rely on.

Studies show that using ecologically-friendly architectural designs such as specialised glass, window film and external shutters could reduce the glaring from skyscraper windows. Legislation on light pollution would also help reduce the collision of birds. 

Active participation by all could ease this problem. Interactive tools are available that allow citizens to report bird deaths, the data gleaned from which is used to map the relationship between skyscrapers and bird collision and assist urban planners to design more eco-friendly urban areas for birds. 

North America has lost 29% of its bird populations- 2.9 billion birds- in the last 48 years. It’s not just the endangered species, even the common birds like sparrows, warblers, and finches have also vanished from the sky, a new study published in the journal Science reveals. Scientists fear that the decline signals a major crisis since birds play critical roles in distributing seeds, disposing of rotting carcasses, and even pollinating plants. 

Bird Population Decline in North America

A team of researchers from the US and Canada analysed almost five decades of population data of 529 bird species collected from multiple long-term bird-monitoring data sets. They found that over 90% of the total decline recorded was among 12 bird families, including sparrows, warblers, blackbirds, and finches. Grassland birds suffered the most with a 53% reduction recorded in their population since 1970. With over 700 million fewer individuals existing today, nearly 75% of all examined grassland bird species are steadily declining. Shorebirds living in sensitive coastal habitats have lost more than one-third of their population. 

Scientists fear that many bird species could soon suffer the fate of the passenger pigeon (Ectopistes Migratorius) —  a bird that once numbered in billions, but silently went extinct in the early 1900s.

“Multiple, independent lines of evidence show a massive reduction in the abundance of birds in North America,” says Ken Rosenberg, the study’s lead author and a senior scientist at the Cornell Lab of Ornithology and American Bird Conservancy. “We expected to see continuing declines of threatened species. But for the first time, the results also showed pervasive losses among common birds across all habitats, including backyard birds.”

Analysing the data recorded by a network of 143 weather radars across North America, scientists also tracked the changes in nighttime spring migration of birds from 2007 and 2017. The radars, which can detect avian migration even in areas where birds are otherwise poorly monitored on the ground, revealed a 14% decline in migratory birds since 2007.

Where did the birds go?

“It’s a wake-up call that we’ve lost more than a quarter of our birds in the US and Canada,” says co-author Adam Smith from Environment and Climate Change Canada. “But the crisis reaches far beyond our individual borders. Many of the birds that breed in Canadian backyards migrate through or spend the winter in the US and places farther south — from Mexico and the Caribbean to Central and South America. What our birds need now is a historic, hemispheric effort that unites people and organisations with one common goal: bringing our birds back.”

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The passenger pigeon

While the researchers did not closely examine what caused the decline, they say the phenomenon in North America is similar to those observed elsewhere in the world, and the causes are likely to be similar.

For example, widespread conversion of grasslands to farmlands and urban areas, and the extensive use of toxic pesticides had earlier caused the decline of grassland bird population across Europe. North American grassland birds today face great threat from such human activities as their breeding and wintering grounds have been turned into agricultural lands and urban centers.  

Previous studies have discovered increasing bird mortality in the US due to hunting by predators including feral cats; collisions with glass, buildings, and other structures; pervasive use of pesticides, and widespread declines in insects — an essential food source for birds. Climate change is compounding these challenges by altering habitats and reducing the number of plant species that birds depend on for their survival. 

Though the study portrays a grim picture, all hopes are not lost. “The story is not over,” says co-author of the paper Michael Parr, president of American Bird Conservancy. “There are so many ways to help save birds. Some require policy decisions such as strengthening the Migratory Bird Treaty Act. We can also work to ban harmful pesticides and properly fund effective bird conservation programs. Each of us can make a difference with everyday actions that together can save the lives of millions of birds — actions like making windows safer for birds, keeping cats indoors, and protecting habitat.”

The study lists out a few promising examples of bird population rebounds. Waterfowl- ducks, geese, and swans- have made a remarkable recovery over the past 50 years in the US after the government allocated funds for wetland protection and restoration. Raptors such as the Bald Eagle have also made a remarkable recovery since the 1970s following a countrywide ban on the pesticide DDT and the introduction of endangered species legislation in the US and Canada. 

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