I spied a fat sparrow . . .

In the Centre City Mall, I saw a fat sparrow. Actually, it was probably an obese sparrow, but you have to allow for feather-fluffing, which can be misleading.

Its breast was more of a rugby-ball than a football-ball shape, and it had at least one lame leg. Hard to say whether that was lame from failing under the weight of the bird, or from not being exercised on a proper twiggy perch because the bird spent too much time in the mall.

The fat sparrow seemed content. It was pecking at some pastry crumbs, the sort of energy-rich, nutrient-poor crumbs on which it had probably become dependent.

Centre City is not bad for a mall. It gets plenty of sunlight and does not have a clinking food dungeon. It's not the worst place a sparrow could spend its days feeding on the detritus of human existence.

Still, I thought of titles for reality-television shows. Downsize My Mall Sparrow, The Biggest Sparrow Loser, Weighing In Sparrows, Extreme Sparrow Diets, Sparrow Boot Camp.

In any of which the weight-loss expert would say, compassionately but firmly, "Here, look at your beak. Your breast might be grossly distended but your beak remains just as evolution intended. Do you see the way it is shaped much like the beaks of the finches? It is designed as a miniature nutcracker; a seedcracker.

"You are meant to be eating seeds, and insects, and that's why we're going to get you back to that place."

"But I love me pastry crumbs," the sparrow would say, his head cocked to one side.

To which the expert would reply sternly, "They are fine as a sometimes food."

About midway through the series, distressed by the expert's insistence on its finding food solely in the outdoors, and by the difficulty it was having in finding seeds or insects in some parts of the urban environment, the sparrow would break down.

"I just, I know it's good for me but I can't handle it," it would confess to a camera mounted above its nest. "I do want to get better."

And then it would wipe its moist obsidian-inset eyes with some under-wing plumage, making for excellent dramatic television.

But would the gains it made in the 10 weeks of filming be sustainable, or would it revert to old habits as soon as the cameras fledged and left the nest?

Evolution might be in its favour, but the human-adjusted environment certainly remained against it.

The producers would have to look at doing a follow-up series in five years' time.