Planet Earth III (BBC1, Sunday) opened with a promise of travel to astonishing wild places, mysterious creatures, spectacular wonders and breathtaking animal dramas.

A small voice from I know not where said, “What, again?”

It seems ungrateful, almost blasphemous, to say Planet Earth has settled into too familiar a routine. Here comes the great escape segment, the cute baby animal standing on its own feet for the first time. Seen it all before, but just look at those fabulous pictures! Good old BBC, this is why we pay the licence fee TV, chunter, chunter, chunter.

The first Planet Earth was 17 years ago, when there was little if any serious competition for the natural history pound. Today, there are entire channels devoted to the stuff. Also making its debut this week was the Netflix series, Life on Our Planet. It is a crowded jungle out there, so why spend close to five years making another Planet Earth?

Two reasons: first, as a species humans are still failing to note the warnings about going to climate change hell in a handcart. The other reason is Attenborough, a giant of public service broadcasting even if he did narrate that other Netflix series, Our Planet, a few years ago.

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In Planet Earth III there is a clip of Attenborough in 1957 on Raine Island, watching green turtles make their life-or-death trek to and from the sea. And here he is, doing the same thing now. This is what Attenborough offers - continuity and perspective. He knows what is happening to the world because he has observed it for himself. He is a walking, talking chronicle of all that has been done and remains to be done. If that means he has to keep making Planet Earths when he is knocking on the door of 100 then so be it.

Three Little Birds (STV, Sunday) is written by Lenny Henry and inspired by the stories of his mother, and others, who came from Jamaica to Britain in search of a new life in the 1950s. The three of the title are Hosanna (Yasmin Belo) and sisters Leah and Chantrelle (Rochelle Neil and Saffron Coomber).

As the ship departs for the three-week voyage to Britain, the trio speculates about what lies ahead. To Chantrelle, who wants to be a movie star, Britain means roast beef and Yorkshire pudding, Elizabeth Taylor and David Niven.

The reality is horribly different. Between the cold, the racism (yes, those posters really were put in windows), and squalor, Leah and Hosanna wonder if they have made a terrible mistake.

The characters knit well and Henry’s script is a watchable blend of soapy and serious and the odd funny line. By the end of the first hour the new arrivals are on their way to Dudley, which just has to be better than London, and secrets from the past are making themselves felt. Shaping up to be perfect Sunday night viewing.

It has been ages since the Saturday night drama slot was filled with anything halfway decent, but I’m going to take a punt and say the drought is over with Dark Hearts (BBC4, Saturday). Given the general strife in the world, it is possibly the worst time to air a series set during the Iraq war, but bear with as Miranda used to say (what is Ms Hart up to these days?).

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The dateline is Mosul, 2016, and French special forces have captured a jihadist who agrees to cooperate in return for safe passage out of the war zone for his daughter and grandson. But first the unit have to find the pair.

The usual briefing follows, with white boards and diagrams and tense glances being exchanged, when who should hove into view but Gilou from Spiral playing the unit’s world weary colonel. Result. If Gilou’s presence is not recommendation enough, the action scenes are blistering and the pace never lets up. Not for the squeamish, mind. All we need now to make Saturdays perfect again is for Laure Berthaud (Caroline Proust) to turn up.

Welcome back River City (BBC Scotland, Monday), or to use the traditional greeting, where the heck have you been hiding? Trying to keep track of when and where Shieldinch will materialise, Brigadoon-style, always keeps fans busy.

Bad news is, the fog of confusion is set to get thicker. The soap, 21 this year, has now switched to a new “multi-series format”, which means three series a year with breaks of six weeks in between. In a classic case of shrinkflation of the kind you usually see applied to biscuits, the budget stays the same but there will be fewer episodes made a year.

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It would never happen to Coronation Street or EastEnders. The point about soaps is they are the old reliables of the schedules. Save for the odd shuffle around for sports, they are always there for viewers when they want to drop by. It’s bad enough that Doctors is to get its jotters, so hands off River City - or Lenny will be round to have a word.