We'll give you a moment to work it out by digressing for a moment to go back to the subject of Canberra's reportedly dwindling population of laughing kookaburras. Newcastle artist and illustrator Laura Arnull has been kind enough to let us illustrate this item with her grand picture of the engaging species.

Loyal readers will know that a few columns ago we reported that BirdLife Australia's new The State of Australian Birds 2015 report was lamenting the declining reportings of sightings of lots of "common" (but popular) birds. The kookaburra, though not formally one of the commoners, was another species reportedly less and less seldom seen. So we wondered how these findings might apply to the famously bird-blessed ACT, and asked luminaries of the Canberra Ornithologists Group.

It emerges that some of the "common" birds BirdLife Australia is worried about (including the magpie and the willy wagtail) are probably as abundant as ever in our little bailiwick (the ACT). But the decline here of kookaburra sightings over the last 20 years is clear. COG luminaries have sent us authoritative statistics and graphs.

The decline doesn't seem to be, yet, a matter of knicker-knotting catastrophe. But it is a matter for brow-furrowing thought. And it gives an extra piquancy, when, now, we do hear kookaburras' maniacal cacklings (although of course this is sometimes one's neighbours). It teaches us that being able to hear kookaburras' calls, this most Australian of sounds, is something precious we must never take for granted.

But back to our quiz question. Get it, anybody? The answer is that the utterly Australian trees and the utterly Australian turbulent post-pubescent boys do, in their various ways, represent Australia overseas. The tree is even sometimes an official, all-Australian gift from our nation to other peoples.

The fact that both boys behave so individualistically on a world stage (at Wimbledon, say, or in Miami) is one of the major beefs that Australian fogeys have with them. Fogeys feel that they let us the nation down and embarrass us.

Meanwhile here in this leafy column we have been running an occasional series on where in the world, far from home, Wollemi pines (world-famous now), have been planted. And Australian readers' reports to us of where they have found them are often tinged with a little national pride. The trees are well-mannered, are always seen (and are strikingly, oddly good-looking) and not heard, and never get into trouble with the local police. It is far easier to have unmixed feelings about them than about Nick and Bernie.

"I believe," reader Alan Robertson reports "that the most northerly outdoor-planted grove of Wollemi pines is in the National Trust for Scotland's Inverewe Garden on the west coast of Scotland."

"This beautiful garden benefits from the moderating influence of the Gulf Stream and contains many Australian species including eucalyptus and callistemon [bottle brushes]. We visited the garden in June last year and can report that the Wollemi pines are thriving."

Marguerite Costello advises that "the United States Botanic Garden in Washington D.C. has some Wollemi pines proudly on display, as we saw last year and showed off to our delighted Washington friends."

Interviewing David Noble, the tree's intrepid, canyoning discoverer (in 1994) at the National Arboretum this week, he testified to having helped plant the trees in Prague, in Budapest and in Bratislava.

And in London. He laughs to remember how at the planting at the Kew Gardens in London he was shown ("You're allowed to just hold it but you're not allowed to use it and get it dirty!") the gleaming, regal spade Her Majesty uses when she does ceremonial plantings.

Credulists' Corner. What is for most of us the mind-boggling Jurassic antiquity of Wollemia nobilis has not boggled the minds of the the Institute for Creation Research.

In its online essay about the tree they preach that "It's hard to imagine how this tree ... could supposedly have been missing for 150 million years. But there's no mystery when this tree's history is understood within God's framework and timescale of Earth history recorded in His Word. Rather than being a living fossil, it is a survivor of the Flood of only 4500 years ago ..."

We look forward to the National Arboretum adding this intellectually-stimulating point of view to the signage at the Wollemi pines' forest 32.

And while on our tennis boys (mentioned above) we see that fogeys keep writing letters to the editor to ask why turbulent Nick Kyrgios and troubled Bernard Tomic cannot be as nice as Lew Hoad and Ken Rosewall were. For younger readers who have never heard of them, we inform that Hoad and Rosewall were Australian tennis stars 150 million years ago in the sporting Jurassic. It was a kind of Wooden Age, for in those olden days Hoad and Rosewall and everyone, including this columnist, played with timber racquets of laminated ash. That age also takes its name from the way in which players were required to show no more emotion than is shown by planks.

But the plank-like stiffness of those times has gone, thank goodness. Lucky enough to have been born into these far healthier, emotionally liberated times in which Nick and Bernie have emerged, then today Lew and Ken would be as entertainingly, bling-wearingly in-your-face as today's two controversial pubescents.