It’s not just humans that like to enhance their appearance: animals have beauty regimes too!
Decorator crabs design outfits
Just like an excited shopper with an armful of clothes, the decorator crab picks up items from the seabed to arrange on its shell. Its hard carapace is covered with Velcro-like bristles called setae that hook on to shreds of seaweed and small animals.
Sponges and colourful anemones are favourites, and the toxins on the anemone’s tentacles are a bonus. This habit is particularly prominent in the smallest specimens who need to camouflage themselves more than the bigger crabs. Some marine invertebrates and ocean plants will settle on the crabs back even without encouragement from their host.
As the crustacean grows, its shell remains the same size. When the time comes to vacate the exoskeleton, the skin inside loosens and the shell cracks. When the new shell forms, the crab picks the decorations off the old husk and recycles them by transferring them to its new home.
Elands soak their heads in urine
The fluffy tuft on the face of the eland is called the hairbrush, and if a male really wants to stand out, he dips it into a puddle of urine. He selects his own waste to smother over his hairbrush, and this is a type of ‘honest signal’. The chemical composition gives other elands information about the quality of the antelope as a mate. It’s essentially an olfactory dating profile for females to judge a male on.
Female elands don’t treat themselves to an ammonia facial, but instead the male gives her hind quarters a good sniff to check she’s as healthy on the inside as she looks from afar.
He performs a behaviour called a Flehmen response, where he traps particles of the female’s urine inside his nasal cavity to make a thorough assessment of her potential as a partner.
Another honest signal eland bulls use is knee-clicking. Elands make snapping sounds with their knees by slipping the tendon over their carpal bone in the forelegs. The tendon acts like a string being plucked, and the pitch of the resulting sound changes as the eland grows larger. The sound communicates the size and quality of the male, prevents attacks from smaller males, and lets the females know who to mate with.
Cuttlefish are cross-dressers
These squid-like molluscs change their appearance to ensure they snare a mate. When a male tries to impress a female,
he changes colour on one side of his body. The edge facing the female is normal, but the male manipulates the side
pointed away from her to display the colouration of another female. This means that an observing male
will assume there are two females in front of him and won’t interrupt the courtship.
This two-faced disguise requires serious brainpower, with the animal focusing on displaying
a dappled brown colour on half of its body and stunning pulsating stripes on the other. This dynamic banding catches the eye of local ladies, and the bold male can even sneak in between a male-female pair that are about to mate. It’s a risky strategy that can lead to fights. It’s also not worth performing for more than one female
at once. The male just can’t keep up the act in front of a larger audience. Cuttlefish display
sophisticated social understanding by saving their best moves for such a specific context, which is
testament to a high level of intelligence.
Vultures dye their feathers
Bearded vultures are famous for dyeing their clean, white feathers on the chest and shoulders with a red colour. It was once thought to be a coincidence that so many of the same species sported the same look, but in 1995 the birds were finally spotted purposely bathing in red iron-rich pools atop the Pyrenees.
It’s unlikely that the vultures need camouflage as they are at the very top of the food chain, and their prey is always dead anyway. Instead it was proposed that the rusty colour advertises the animal’s strength as it demonstrates their ability to seek out a rare iron oxide deposit. Another idea is that iron somehow kills the huge variety of bacteria these birds encounter when feeding.
We do know that the bone-based diet of the bearded vulture doesn’t provide enough carotenoids – the same pigment that makes flamingos so pink – and the birds might be trying to make up for this shortage.