This weekend's viewing: Attenborough's Ark, Friday, BBC2; Homeland, Sunday, Channel 4

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Not all endangered species stir affection in us, but there's absolutely no doubting that this one does: Attenborough Avuncularis, the silverback of natural-history television, now celebrating an astonishing 60 years on screen. For most viewers, his image is as closely associated with public-service broadcasting excellence as the panda's is with the World Wildlife Fund – he's a kind of living logo of high-minded pleasure. But the natural habitat for this kind of broadcaster may be shrinking and he has no obvious successor. As a result, you watch every programme with an odd feeling of premonitory nostalgia, wistful at the thought that he won't be around for ever.

More listen than watch to be honest, because old age has restricted the extent to which he can travel, and these days he more often narrates over footage of younger men clambering through the jungle than doing any clambering himself. He did appear among the foliage in Attenborough's Ark – in which he was asked to nominate the 10 endangered animals he would most like to save from extinction – but it looked distinctly zoo-like to me, presumably the best way of getting Attenborough's unforced delight in live animals on screen without taking the risk of actually killing a national treasure.

He explained that he wasn't going to go for the obvious choices, the A-list of endangerment. He gave a name-check to headline stars such as the snow leopard and the mountain gorilla, but his selection was more concerned with naturalist's fascination and ecological explanation. The black lion tamarin, for instance, is a fetching animal in its own right, but also provided the justification for an account of an attempt to preserve its habitat by linking isolated forest "islands" together with highways of reforestation. Other animals made it in for their oddity, such as the solenodon, a prehistoric mammal with a nose that's an early prototype for a trunk, or the olm, a subterranean reptile that looks like white asparagus with legs.

There were some bigger beasts too – the Sumatran rhino and the pangolin – but it was at its best when it reflected Attenborough's omnivorous pleasure in the natural world. He included Darwin's frog, the male of which species carries fertilised eggs in his own vocal tracts until it's time to spew the little froglets out into the world, and the northern quoll, an Australian mammal into which someone is laboriously breeding an aversion to cane toads, because they haven't yet quite worked out for themselves that they're poisonous. He also indulged himself with a Priam's birdwing butterfly, despite its drastically limited lifespan, because "butterflies lift the heart". So do Attenboroughs, as it happens.

Fans of Homeland have had a difficult couple of weeks as the writers seemed to be deliberately trying to dislodge us with increasingly ridiculous plotlines. It's been like riding a bucking bronco, frankly, and after Brodie took a shower in a car-wash I very nearly lost my grip on the saddle entirely. The horse calmed last week – with a long intense episode in which Carrie confronted Brodie in an interrogation room – and last night's episode was better too, exploring the interleaved layers of attraction and suspicion the two central characters feel towards each other. But I'm not dropping my guard yet. I can't see the point of the new sub-plot, which involves Brodie's daughter in a hit-and-run accident, unless it's to give the writers a break from untangling the mare's nest of narrative strands they've got themselves tangled in. And I am beginning to feel that I've watched Claire Danes' face buckle into misery one too many times. But the series can still pull off an unexpected jolt – as with last night's massacre in the Gettysburg tailor shop. Not sure yet whether it's trying to shake me off again or just liven things up, but I'll stick around to find out.