All sensitive Canberrans love this city's magpies and thousands of us have special relationships and feeding rituals with "our" magpies in our gardens. But Fernon has taken her fondness for magpies to another level with this mosaic letter box.

"I've been lucky enough to have formed a close bond with two magpies over the years and they are now trusting enough that they follow me into the house and snatch up anything I've left on the kitchen floor for a snack. In their honour I've created a magpie mosaic on my letterboxes. Other birds on the letterboxes are two birds of paradise, a wren and a lorikeet."

"I feed the magpies (gourmet) mince and give the cat a bit too. When I'm at home and the cat's outside and the magpies come for a feed, the cat bangs on the door to let me know they're there and everyone gets a feed. Over the years the menagerie has grown, a local raven comes around for a bite now."

Ah, ravens! The Australian raven (the ubiquitous big, black, carrion-munching bird most of us call a "crow") builds almost the most conspicuous birds' nest (a great big tangle of quite big sticks and twigs) Canberrans ever see in a Canberra tree. If you are lucky there is a new one, now, in a tree near you.

But why do our ravens nest in trees and why do they never, unlike so many of their northern hemisphere corvid cousins, nest on the faces of cliffs? Can they be afraid of dizzying heights, of precipices? And we can ask the same probing and investigative question about our wedge-tailed eagles. Elsewhere in the world eagles of our wedgies' Aquila genus make nest on cliffs while Australia's wedge-tailed eagles never do this (they nest in trees), although very occasionally coast-based wedge-tailed eagles take over a cliff-face nest previously built by white-bellied sea eagles, fowls of a different genus.

Canberra's Jerry Olsen, a well-travelled world authority on raptors (and the source of our information for Monday's column all about the smorgasbord of things on wedge-tailed eagles' diets) wonders about these questions in his book Australian High Country Raptors. He travels the world looking at the Northern Hemisphere's raptors and of course is very familiar with Australia's, and in his book wonders "What do Australian raptors and corvids [our ravens] have against cliffs?"

Everywhere he goes in the northern hemisphere he finds raptors and ravens nesting on cliffs "But Australian Aquila and Hieraaetus eagles and corvids such as the Australian raven, don't build nests on cliffs. They don't seem to know how to ..."

At first he wondered if the explanation might lie in Australian geology, with our cliffs being older, smoothed by time, smaller than and different from foreign cliffs. But then as someone who knows his Australian cliffs and who has clambered around on them for decades while visiting nests of the peregrine falcons, "you see plenty of ledges big enough to hold an eagle nest and many ledges big enough to hold a large motor car". And so he's sure there's nothing about our cliffs that explains why our eagles and our corvids and lots of other species boycott them.

Perhaps, he speculates, it's not that our cliffs are inferior to the world's but that "Maybe in our eucalypt-dominated Australian landscape we have superior trees" that our cliff-shunning species prefer. On his overseas peregrinations (and I use that word advisedly) he finds raptors of Spain, Portugal, California and Arizona showing great enthusiasm for introduced eucalyptus trees for nesting purposes.

Then perhaps, he muses, it is that Australian raptors and corvids have been isolated for so long from their northern hemisphere cousins that ours have lost the ability to build nests on cliffs, or that, during this separation, their northern hemisphere counterparts learned it. It is a mystery.

But Australian ravens are so famously intelligent (look at the intellectual glint in the eyes of the cafe-haunting Botanical Gardens' raven in Julian Robinson's grand photograph) one almost feels one could ask one what its species has against cliffs and that one would get a lucid explanation.