Sacrificing wetlands to build a new technology hub in the northern part of Hong Kong could cause "irreversible damage" to the habitat of endangered black-faced spoonbills, an environmentalist group warned on Friday, although it reported a rise in the number of the rare migratory birds found in the city.

The Hong Kong Bird Watching Society's director, Yu Yat-tung, said wetlands in Hong Kong could not be reduced further, voicing concerns that filing in fishponds for the San Tin Technopole project could result in the largest wetland loss in the past three decades.

"We are talking about a zero loss of wetlands. I think this is a very important policy for us to work towards wetland conservation," he said. "We need to make sure that no wetland can be lost in any development projects from now on and the future."

His comments came as an annual census conducted in January by the society found 6,988 of the rare migratory birds across the world – a 5.4 percent rise from the year before – marking the third straight year that such figures surpassed 6,000.

In Hong Kong, 375 were spotted in the latest study, up by a quarter from the previous year. But the number of migratory birds in the territory only made up around five percent of the global population.

"[The figure] is just returning to the previous, normal range of black-faced spoonbills. In the past 10 years, we could usually have about 300 to 400 black-faced spoonbills wintering in Hong Kong," Yu said.

"We hope the situation can further improve in the coming future, so we need to do many more wetland conservation activities to make sure this can happen."

Taiwan was once again the top winter destination for black-faced spoonbills, with nearly 60 percent of the bird's worldwide population, even though the total number found there dropped slightly.

The mainland attracted 1,630 spoonbills this year, while Macau recorded the largest decline of 38 percent.