Millennials think a specific sound of their childhoods has disappeared. As soon as I heard it again on TikTok, I had to find out why.

• A bird call has gone viral and taken people who grew up in the 2000s right back to their childhoods.
• I remember the same sound waking me up as a kid and soundtracking my teenage years.

There's a specific sound that followed my generation through our collective childhoods, and many of us are wondering why we haven't heard it since.

If you're a millennial who grew up in around the 2000s, perhaps especially in the UK, you might know exactly what I'm talking about. The distinct woodpigeon call.

Described simply as "Bird sounds - Pigeon" on TikTok, it's a sound that's gone viral online and featured in over 25,700 videos. Users have reminisced about the familiar tune which greeted them each morning as they got ready for school.

Others have used the bird call as a backdrop for nostalgic slideshows of childhood memories sparked by the sound, like time spent at sleepovers with friends or playing in paddling pools, and the snacks they remember from those halcyon days.

I remember it vividly too.

It was one of the first sounds I heard when I woke up as a kid in Wales throughout the late 1990s and early 2000s. It takes me back to those blue-sky mornings, when Saturdays and summers seemed to stretch on forever.

It's the same sound I heard in my teens, waking up after camping in a random field. It followed me home in the early hours after house parties too, like an avian ambassador for my adolescence, seeing me to my front door.

It's a sound I haven't heard in years, and I'm not alone.

Some have tried to pinpoint the exact period the call reminds them of, hyper-specifically suggesting it's the sound of the summer of 2013. There's been debate about the year in the comments, but it's generally agreed to bring back recollections from the early 2000s to mid-2010s.

Multiple TikTokers have insisted it was especially ubiquitous in the United Kingdom during that time, while popular comments on similar videos have pointed out it's a shared experience for people in countries including Lithuania and the Netherlands too.

On November 16, a TikToker who goes by @freya101freya posted a video featuring the sound with an on-screen caption that read, "Its just a bird calm down?" while a further caption read, "2000s kids:" just above a clip of former CEO of WWE Vince McMahon getting upset, a meme often used to indicate someone is too emotionally invested in a particular topic to discuss it.

The video racked up 490,000 views in one day, and over 350 comments which once again revelled in the nostalgia of the bird call, and agreed it especially resonated with people who grew up during that time.

"But why is this just a thing for our generation, why don't we hear it now and why didn't our parents hear this!!" one viewer wrote in a popular TikTok comment, as many more agreed the sound seems to have disappeared in recent years, which has caused it to become such a specific checkpoint of our childhoods.

Viewers put forward multiple theories, suggesting maybe noise pollution had drowned them out, or we were too wrapped up in our adult lives to pay the birds of our youth any attention, or that they had simply flown away.

I wanted to know if this was the case, so I tracked down a wildlife expert and asked.

"Woodpigeons may not be the most typical representation of childhood nostalgia, but they have experienced a 5% decline between 2010 and 2020," Barnaby Coupe, land use policy manager at The Wildlife Trusts, which operates in the UK, told Business Insider.

This could be why the sound of them is less common now than it was in our childhood, but it's perhaps not the only bird sound millennials will remember from a bygone era.

"Unfortunately, this is a relatively positive figure compared to the 58% average decline of farmland birds since 1970," Coupe said of the woodpigeon decline. "Agriculture policies which have promoted an intensification of our countryside are the primary reason for this stark decrease in population, by destroying habitats and pushing farmland birds from the landscape."

Coupe called for government support for "nature-friendly farmers" which he said needed to be "implemented rapidly and at scale to halt and reserve the catastrophic decline of farmland nature."

Whether we notice or not, it seems likely that bird calls in general have faded from many of our lives. Perhaps that's why, for people like me, the TikTok sound has become such a nostalgic gathering place.