It's hard to start a conversation with a stranger—especially when that stranger is, well, different. He doesn't share your customs, celebrate your holidays, watch your TV shows, or even speak your language. Plus he has a blowhole.

In this episode, which originally aired in the summer of 2014, we try to make contact with some of the strangest strangers on our little planet: dolphins. Producer Lynn Levy eavesdrops on some human-dolphin conversations, from a studio apartment in the Virgin Islands to a research vessel in the Bermuda Triangle.

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For much of history, tree canopies were pretty much completely ignored by science. It was as if researchers said collectively, "It's just going to be empty up there, and we've got our hands full studying the trees down here! So why bother?!"

But then, around the mid-1980s, a few ecologists around the world got curious and started making their way up into the treetops using any means necessary (ropes, cranes, hot air dirigibles) to document all they could find. It didn't take long for them to realize not only was the forest canopy not empty, it was absolutely filled to the brim with life. You've heard of treehouses? How about tree gardens?!

This week we journey up into the sky and discover Forests above the forest. We learn about the secret powers of these sky gardens from ecologist Korena Mafune, and we follow Nalini Nadkarni as she makes a ground-breaking discovery that changes how we understand what trees are capable of.

P.S. This episode is a layer cake of arboreal surprises (including the reappearance of a certain retired host).

A few visual tre(e)ats:

We first learned about the magical world of the canopy from this beautiful video from Michael Werner, Joe Hanson, and the PBS Overview team. It features Korena Mafune’s research up in the treetops, as well as the people who have dedicated their lives to saving what’s left of the old growth forests. We highly recommend checking it out! And, if you’re hankering to go climb a tree after this episode, you might enjoy browsing Hallie Bateman’s wonderfully illustrated guide to the best climbing trees in NYC for a little inspiration.Support Radiolab by becoming a member today at Radiolab.org/donate.Radiolab is on YouTube! Catch up with new episodes and hear classics from our archive. Plus, find other cool things we did in the past — like miniseries, music videos, short films and animations, behind-the-scenes features, Radiolab live shows, and more. Take a look, explore and subscribe!

Jad started Radiolab roughly 20 years ago. And now he is stepping aside from hosting and producing the show to replenish, to think, to rock in his chair and be with his kids and wife, and maybe make some music. The news has been all over twitter and there’s a letter from Jad and our hosts Latif and Lulu on the website. But in this episode, Jad talks through his decision to leave and the future of the show with Lulu and Latif. And then, as a parting gift, we play him the very first episode of Radiolab (“The Radio Lab” as he called it then). He tells us about biking the CDs over the Brooklyn bridge just before the show was supposed to air, reading the news and weather between segments, and then we just sit back together and listen to where it all began.

Jad, for those of us who have been radically changed by the thing you put out into the world, we are both sad to lose you in our ears and endlessly grateful for what you’ve given us.