Hong Kong’s rat problem tackled with new AI and hi-tech surveillance equipment

Hong Kong authorities have turned to hi-tech surveillance techniques to track rat activity – a method said to be more accurate than the former approach of using sweet potato as bait.

Authorities on Tuesday said they had deployed thermal cameras and artificial intelligence (AI) technology to more accurately measure the rodent problem across the city.

“In the past, we could only see the distribution pattern of rodents and could only tell whether there was a rat by looking at the sweet potatoes,” Lee Ming-wai, the pest control officer in charge at the Food and Environmental Hygiene Department, said.

Lee added the old system failed to show how serious a rodent infestation was in an area.

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One of the new camera rigs deployed in the battle against rat infestation in Hong Kong. Photo: Handout

The scope of the surveyed areas was limited and bait could also be affected by human activity or other animals.

“The new method of using thermal cameras could tell whether there were rodents in each image with the use of AI,” Lee explained.

Department officials added that, instead of counting the ratio of the sweet potato baits that had been gnawed by rats to come up with the infestation rate, the problem would be measured by the newly designed rodent absence rate, based on the number of thermal images that did not detect the pests.

Two thermal cameras, mounted on a two-metre (6.5-foot) pole, are installed at a location and capture an image every two minutes from 7pm to 7am for three nights in a row.

By counting the number of thermal images with no rodents among all images taken, a rodent absence rate is generated for each area.

Rats and sweet potatoes: why Hong Kong’s rodent count doesn’t add up

Warner Cheuk Wing-hing, the deputy chief secretary, said in 2022 that the sweet potato bait method had “insufficiencies” in measuring rodent infestation rates.

Stella Cheung Lai-han, a statistician from the department, said that looking at the no-rodent rate would be more accurate in reflecting how widespread rats are.

“It is impossible for us to tell how many rodents are there at a location,” Cheung added.

“If a rodent appears repeatedly, we can only count the appearances of the animals … and this could exaggerate [the actual situation].”

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The cameras will allow for more precise estimates of Hong Kong’s rat population. A rat is visible in yellow-white in the top of the image. Photo: Handout

Tommy Lam Tsan-yuk, an associate professor in the University of Hong Kong’s school of public health, who looked into the latest method for rodent surveillance with the department, said the new technology could record the number and movements of the animals, and provide information on different locations and time points.

Around 200 to 300 surveillance spots will be identified in each of 19 areas managed by the department, and 100 locations chosen for each round of the survey, which is done every six months.

The locations were picked based on the number of live rodents captured and dead animals collected, as well as by complaints received. The list of targeted sites will also be updated on a regular basis.

What is Hong Kong’s rodent infestation rate and why is it under fire?

Wilson Ng Kwok-lun, a senior superintendent in cleansing and pest control at the department, said more targeted measures could be deployed with the new information.

He said pest control teams could be assigned to kill rodents at night time when the animals are most active, and deploy poisonous baits during daylight hours.

Wan Chai, Central and Western, and Eastern districts started to adopt the new approach last month.

Ng said statistics gathered using the new method on the three districts could be announced as early as next month.

The department said it is working on the first citywide rodent absence rate survey and that it was hoped to announce the findings in the first half of the year.

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