‘Every lost life is a lost life': University of Hong Kong scholar studies why campus is hotspot for bird-window collisions

HKFP

03-05-2025

In a laboratory of the School of Biological Sciences at the University of Hong Kong (HKU), Professor Juha Merilä put on a pair of rubber gloves, took some brown envelopes out of a refrigerator, and placed them on a tray. From each envelope, he carefully extracted a plastic bag, each containing a deceased bird.
'This is a Swinhoe's white-eye,' he said, gently placing one small bird after another on their respective envelopes. The two birds had yellow-olive upperparts and pale grey underparts. A piece of paper was attached to each envelope, marking the date, species, location, and suspected cause of death.
The carcasses of the two birds were found and collected on the same day in January at the Sun Yat Sen stairs, right next to HKU's Knowles Building, located just below a connecting bridge with a row of glass windows.
They likely died after colliding with the building's windows, said Ton Yeh, a part-time birdwatcher working with Merilä to record and compile data on bird strikes on campus.
Merilä – a Finnish scholar specialising in ecology and biodiversity – has been collecting and monitoring data on bird-window collisions on the HKU campus for the past two years, aiming to map unnatural bird deaths, identify reasons for the high occurrence, and analyse patterns.
Based on his own tally, as well as figures from the government and other sources, at least 152 birds have been found dead at several locations at HKU over the past five years.
Located at the western end of the Mid-Levels district, the 114-year-old university is famous as Hong Kong's oldest higher education institution. Little known is its reputation as one of the sites that pose a deadly threat to flying birds in the city.
The HKU campus, dotted with modern glass-panelled buildings, is one of the bird-window collision hotspots in Hong Kong, Merilä said.
He chose to focus his research on HKU partly because of the accessibility, partly to collect more comprehensive data following an earlier study about bird collisions, conducted by nonprofit Hong Kong Bird Watching Society (HKBWS).
'We are hoping HKU can be a model to hopefully extend what we've learnt [here about bird collisions] to other areas of Hong Kong,' he said.
'Preserving, protecting birds and other wildlife gives positive benefits for humans. Biodiversity matters for our well-being and that of birds, as part of the ecosystem which provides for us,' Merilä said.
Between September 2022 and August 2023, the HKBWS carried out surveys in five locations across Hong Kong: HKU, the Chinese University of Hong Kong (CUHK), Mei Foo, Tsing Yi, and Tsim Sha Tsui, combining them with data from public reports.
A total of 284 birds were killed and 25 injured in 16 districts during the one-year period, according to a report the NGO published in September.
A large-scale survey of bird collisions that covers all districts is needed for a comprehensive analysis of the risk factors for incidents specific to Hong Kong, said Wong Suet-mei, senior conservation officer at the HKBWS.
Currently, data collection on bird strikes heavily relies on voluntary reporting by members of the public, she added.
Binocular vision
Merilä's efforts to document dead birds on campus found support from the student-run Ecology & Biodiversity Society (EBS), part of the HKU student union. In January, the society published an essay unpacking the reasons behind the deaths of over 150 birds on campus since 2020, citing his study. It was widely shared on social media, racking up over 40,000 views.
'We have a rich biodiversity of bird species around the HKU campus and near Lung Fu Shan Country Park, where birds pass by or rest,' said Vanessa Ng, an EBS spokesperson.
However, she added, most students were oblivious to bird-window collisions and were surprised to learn that their school was a hotspot.
Birds are sometimes unable to perceive glass panels while flying due to their physical traits, the HKBWS explained in its report. With eyes positioned on each side of the head, a bird's anatomy restricts its binocular vision, resulting in a weaker perception of distance and three-dimensional space.
When flying, birds may have difficulty recognising glass panels as an invisible barrier, causing them to strike the glass.
Unlike roadkill, the bodies of birds found after glass collisions are not deformed. During the collision, birds are usually killed because their beaks are pushed into their heads, Merilä said.
Collision black spots
Bridges cause many bird strikes on the HKU campus. One of them is a skybridge on the fourth floor of the Centennial Campus. A flock of 15 Indochinese Yuhina birds crashed into the glass windows of the skybridge in early April 2023.
It was the largest recorded number of bird collisions on a single day on the campus, according to data compiled by Merilä. (According to the HKBWS report, 71 Indochinese yuhina birds died from such impacts across Hong Kong in 2022-23, the highest among all avian species.)
Other collision black spots include a skybridge between the Library Building and the Knowles Building, the Kadoorie Biological Sciences Building, the Chi Wah Learning Commons, and Swire Hall.
Shorter structures with glass windows situated near trees and other vegetation, like the Rayson Huang Theatre building right next to the Lily Pond, are also potential culprits, as the reflection of the trees on the glass windows can create a 'false impression' or a 'misleading visual cue' for the birds, Merilä said.
Migrating birds accounted for over 60 per cent of collision victims in the city, according to the HKBWS. Among them were critically endangered or protected species.
'Hong Kong attracts tens of thousands of migratory birds to stopover and refuel energy every year,' the HKBWS said in September, when it released its 52-page report. 'But at the same time, Hong Kong being a high-density city and the high-rises with extensive glass may unfortunately turn out to be fatal traps for migrating birds.'
This was evident in the bird species found dead at HKU. The Indochinese yuhina is a protected species that carries out seasonal migration in groups.
Other migratory birds found dead and injured on the campus included the yellow-breasted bunting, a critically endangered species, as well as the northern boobook and the bluethroat, both Class II protected species in China.
At HKU, deaths of less common migratory bird species like the lanceolate warbler or the narcissus flycatcher were also recorded.
For Merilä, it makes little difference what a bird's status is. 'Every lost life is a lost life,' he said.
Window stickers
Bird-window collision is a worldwide phenomenon, and it has become one of the leading causes of unnatural deaths among wild birds. South Korea's Ministry of Environment estimates that around eight million birds die in the country each year from flying into windows. In the US, the annual figure exceeds a billion birds, according to a study published in the journal PLOS One last year.
Activists, conservationists, and authorities around the world, such as in South Korea, Taiwan, the Philippines, the US, and Canada, have resorted to installing visual markers like patterned stickers or decals on external glass surfaces to help birds avoid crashing into them.
Merilä applied for university funding to install anti-bird-collision stickers on glass windows at one hotspot but was rejected due to high costs.
The stickers are inexpensive, but the scaffolding and manpower required to properly install the stickers on the outside of the glass windows is 'where the cost comes [in],' he said.
The professor managed to piece together funding to put window stickers at one hotspot on campus. The installation is scheduled to be completed later this year.
'If we can show that [the method] reduces the kill rates in this particular locality, that could maybe give an incentive for the university to also consider putting them in other places where birds get killed,' Merilä said.
As Wong pointed out, public pressure could make a difference.
In its 2024 report, the HKBWS documented a total of 30 bird deaths and collision imprints due to window strikes at Mei Foo MTR Station in four months. Afterwards, members of the public reached out to MTR Corporation (MTRC), appealing for improvements, Wong said.
In December that year, the MTRC began installing anti-bird-collision stickers on 121 high-risk glass panels at Mei Foo Station. The rate of bird-window collisions at the station later dropped by 90 per cent, Wong said.
'If each citizen tells their management company to install glass window stickers, maybe gradually more people will accept the stickers and at least save some [birds'] lives,' she said.
Another challenge is maintaining or replacing old window stickers with new ones, highlighting the importance of choosing a long-term solution.
A more sustainable alternative, Wong suggested, is to include anti-bird-collision glass materials as early as the design stage, or to stop using reflective and transparent glass windows.
Citizen science
Public involvement in scientific research, also known as citizen science, could be the next step for bird-window collision studies.
In 2021, a Canadian nonprofit launched the Global Bird Collision Mapper (GBCM) website, a worldwide database and free geo-mapping tool for people to report sightings of bird collisions.
Collected data 'are used in research and education worldwide, aimed at understanding and mitigating these tragic incidents' and eventually 'to create the path toward a future where birds thrive alongside urban landscapes,' it said.
The HKBWS has written a manual on how to report a bird window collision through the GBCM website.
'As an urbanised international city, Hong Kong has a responsibility to conduct research or citizen science work on the issue,' Wong said.
The HKBWS made use of the GBCM data that was submitted by members of the public, incorporating it into its 2024 report.
Ng of the student society said that she paid more attention to bird deaths in general, be it roadkill or window collisions, after learning about bird collisions at HKU.
Since January, she has encountered two suspected bird deaths outside the campus. She reported both cases to the Agriculture, Fisheries and Conservation Department.
It might be a small part, but it was still an important thing to do.