Country diary: A streak of lemon on a drab moorland day | Ed Douglas

Perhaps in sympathy with the changing clocks, cloud had blanketed the moor, bleeding colour from the woods beneath, the light fading before it had properly arrived. It seemed one of those days when nothing much would happen, the sort that might put a hole in your mood. And yet, as the afternoon wore on, the blanket thinned and colour returned, like someone unexpectedly turning up a dimmer switch. The yellowing birch leaves sparked into life and, easing my way down steep ground, I kicked over a Russula cyanoxantha, a charcoal burner mushroom, its cream-tinged underside glowing brightly in the preternatural dusk. Movement in the birches dragged my attention away. A goldcrest was working its way down a branch – Britain’s smallest bird, with its tiny, liquid song. The unusual light was burnishing the narrow yellow stripe crowning the goldcrest’s head, its lemon tone suggesting a female, since the male’s is more orange. This streak of colour hummed with strange intensity, even against the glowing birch leaves, a strip of luminescence across the tissue-thin skull that gave this slightest of creatures a mighty presence. Goldcrests, like many other birds (including flamingos), get this colouration from carotenoids they consume in their diet, in this case, tiny invertebrates and insect eggs. These chemicals, being antioxidants, also improve the bird’s immune function, but there’s a trade-off between health and breeding success and the intensity of colour – at least for the males. Testosterone likes a show, so male goldcrests spend more of their energy processing carotenoids into the brighter orange crests that attract a mate. The stronger this colour, the better the chance a female will respond, sensing superior health and foraging ability. That’s just what she needs to nourish the large number of chicks that she’ll produce in spring: 10 or even a dozen in each of two broods – the second under way even before the first has fledged. Each chick weighs barely half a gram when they hatch, naked and blind, and reach the adult weight of 6g in a fortnight. Judging by her vibrant crown, this queen of birds looked more than capable of surviving the winter. • Under the Changing Skies: The Best of the Guardian’s Country Diary, 2018-2024 is published by Guardian Faber; order at guardianbookshop.com and get a 15% discount