Taiwan's military has grown used to the daily task of tracking Chinese warplanes flying near the island. Some days there are a handful. On others, many more. But they are a near-constant presence.
So when the aircraft suddenly stopped coming for nearly two weeks, the silence was both striking and deeply puzzling.
That spell was broken on Thursday with five People's Liberation Army (PLA) aircraft operating around the Taiwan Strait over the previous 24 hours, according to Taiwan's military, with several flying near the median line that divides the waterway.
Analysts say it was the longest pause in Chinese air activity since Taiwan began publicly releasing daily military data.
"This is frankly unlike anything we've seen in recent history in terms of PLA activity around Taiwan," Ben Lewis, founder of PLATracker, an open data platform that tracks Chinese military movements around Taiwan, Japan and the South China Sea, told CNN.
"Since Taiwan's defense ministry began releasing this data in 2020 the trend has been up, up, up," Lewis said. "And now this lull, which maybe has ended today, maybe not, represents a very significant change in the pattern."
Beginning February 27, Taiwan recorded 13 consecutive days without Chinese warplanes flying near the island.
One brief exception came on March 6 when two aircraft were detected in the far southwestern corner of Taiwan's air defense identification zone, but analysts say the broader pattern still represented a striking break from recent years of steadily increasing Chinese military activity.
The sudden quiet puzzled analysts and raised a range of possible explanations.
One theory is that Beijing may be trying to avoid escalating tensions ahead of a planned meeting later this month between Chinese leader Xi Jinping and US President Donald Trump, where trade, technology and Taiwan are expected to feature prominently.
"If I was in Vegas, I would put it on the Trump visit," Lewis said.
Others have pointed tothe war involving Iranand the potential impact on global energy markets, though analysts say that connection is less certain.
Some observers also note that China's annual parliamentary meetings, known as the "Two Sessions," are concluding this week, a period when military activity has occasionally slowed in the past.
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Taiwan's defense minister Wellington Koo urged caution about drawing conclusions from the lull, noting that Chinese naval activity around Taiwan has continued throughout the period.
"There are a lot of theories out there," Koo told reporters on Wednesday. "But we still see Chinese naval vessels operating around Taiwan on a daily basis, and these efforts to turn the Taiwan Strait into China's internal waters have not stopped."
Indeed, Taiwan continued to track several Chinese warships operating around the island throughout the period, even as the skies above remained unusually quiet.
Lewis said the limited number of aircraft detected Thursday may not signal a full return to normal activity.
The flights came the same day a US Navy P-8 surveillance aircraft transited the Taiwan Strait, in what the 7th Fleet says is a demonstration of Washington's "commitment to a free and open Indo-Pacific," and the Chinese planes may have been deployed simply to monitor the American aircraft.
Even then, the response appeared muted compared with past incidents when US ships or aircraft passed through the waterway.
"Relative to previous incidents when the US Navy transited the Taiwan Strait, the number of Chinese aircraft deployed today was actually quite low," Lewis said.
That uncertainty leaves analysts watching closely to see what happens next.
Over the past five years, Beijing has dramatically increased the number of aircraft it sends near Taiwan, gradually normalizing what once would have been considered major military incursions.
On some days, Taiwan has reported dozens of Chinese aircraft operating near the island.
In that context, Lewis said, the sudden disappearance of the flights has been just as striking as their return.
"It used to be that five aircraft would make headlines," he said. "Now we're talking about zero, and that's what's unusual."
For now, the mystery remains unsolved.
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