Specimen Showcase｜The Flying Sapphire
- Hong Kong Biodiversity Museum
- Apr 9
- 4 min read
Deep in Hong Kong’s wetlands 🌳 and shrublands a living gem 💎 is gazing at the water surface, waiting for a fish or perhaps an insect to come by.
Under today’s limelight is 𝘏𝘢𝘭𝘤𝘺𝘰𝘯 𝘴𝘮𝘺𝘳𝘯𝘦𝘯𝘴𝘪𝘴 (Linnaeus 1758), commonly known as the white-throat kingfisher. Measuring up to 29 cm, this is not the largest bird around but, without a doubt, you will not miss it when flying, as it wears a striking coat of brightly iridescent blue feathers 🔷 on its back and a white “collar” on its chest ⚪️. The plumage is not the only part of this bird that is colourful, as its thick beak is also brightly red coloured 🥢. Certainly, calling them a flying gem 💍 would not be an overstatement.
Yet under the fabulous looks of this bird hides an astute predator 🕵🏻. As its common name implies, these birds are experts at catching fish🎣. White-throat kingfishers would sit and wait on a branch (perch) gazing at the water surface. When a fish swims by, they would plunge to capture their meal 🤿. However, if you have ever handled a live fish, you will know that they are very slippery to grab 🐠 and would wiggle non stop to escape. So how do kingfishers solve this problem? They simply smack the fish against the branch they are sitting on repeatedly until it passes out 😵💫, and then reorientate the fish so that the head can be swallowed first. The reason behind this meticulous reorientation is that fishes have a row of spines on their fins 🗡️; if swallowed tail first, the fins would go erect and pierce the delicate oesophagus of the bird 🤕.
To feed on fishes, and to prevent their prey from wiggling 🍽️ out of their mouth, kingfishers have evolved to possess tiny barbs on their tongue which lock the prey inside their mouths 🔒. Additionally, their throats are lined with mucus glands to lubricate the fish for easier swallowing. Are kingfishers feeding only on fishes as their name may suggest? No! Scientists also frequently documented these birds feeding on a wide variety of animals 🍴, ranging from aquatic organisms like crabs 🦀 and aquatic insects, to frogs 🐸, lizards, smaller sized birds (white-eyes) 🐥 and even mice 🐁.
These birds are, however, probably most conspicuous when flying over the water, looking like a blue flash in the landscape. The blue colour of the birds’ spectacular feathers is produced by structural colour 🦋. It results from small sponge-like structures on the feathers scattering blue light when under a lightsource. This colour does not fade as it is produced by the structure of the feather, not by a pigment which may degrade over time.
You may be intrigued, however, about the function of such bright blue colours. First, let’s note that the white-throat kingfishers possess sexual dimorphism; meaning that the two sexes have different external features 🔍. This is where the bright feathers come into play. The male kingfishers have a more saturated and vibrant blue colour 🎨compared to the females, and the brighter the blue the more attractive the individual is to the females. But how do they make themselves more vibrant? Below the layer of structurally blue feathers lies a layer of brown feathers that absorb the non-blue (unscattered) light that passes through the “blue” feather layer. As a result, the blue colour looks more saturated 🟦. For the male kingfishers though, the production of this brown colour (melanin), which is a biological pigment, requires energy. In other words, excess melanin makes them look more blue, but it takes more energy and effort to maintain a high level of melanin💥. Hence having a more saturated blue plumage is a visual cue to signal that the male is physically strong and good at survival 💪🏻. When it comes to « impress 💍» the females, looks are not the only cue used by females to choose their mate. Moves are equally important 🕺🏻, and males will begin flashing their feathers, followed by a head bopping “dance” to attract females. If it works, the female will approach. Then the newly formed couple will fly together💃🏻 and chase each other, offering each other fish they caught🎁.
Time to form a family 🏠, and for nesting these birds prefer to dig a nest in a vertical sloppy sandy loam cliff 🧗. However, it is not quite safe yet. Predators can easily locate their nest. After all it is just a hole on a barren cliff. To trick predators, the witty kingfishers would build around 5 false-nests without eggs near the true one with eggs, tricking 🤡 the predators into thinking that the nests are already abandoned. Scientists also observed that the closer the true nest are to vegetation 🌾 the more false nests the parents will build, possibly reacting to the higher density of predators around 🐍.
Want to take a glimpse of the fabulous flamboyant 👨🏻🎤feathers of this hidden gem, come to the Hong Kong Biodiversity Museum and you will find the white-throated kingfisher standing on a branch, ready to strike. And if you enjoy this post, please share it with friends and follow us for more amazing biodiversity stories weekly. 🙌
Text: Hugo
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