I am, by any reasonable measure, an embarrassingly heavy sleeper. Sam will tell you — and has told many people, usually at my expense — that I could sleep through a small natural disaster. Under normal circumstances, this is probably true. I hit the pillow, and I am gone. No lingering, no overthinking, no lying awake cataloguing the day. Just out.

Samantha, on the other hand, is a light sleeper of almost supernatural ability. The faintest sound, a shift in the room, a child turning over two doors down, and she’s awake. Before kids, this manifested mostly as mild irritation at my ability to be unconscious within thirty seconds of lying down. Since kids, it has become something else entirely. Something more wired, more alert, more animal.

Probably my favourite photograph from the afternoon. The way she gracefully positioned herself on the fallen branch made me think that she may have used this tree for a rest before…

Because here’s what I’ve noticed: Samantha used to need a runway in the mornings. Coffee was non-negotiable. Conversation before coffee was a risk you took at your own peril. She was a slow starter, elegant, but slow. Certainly, since Olivia arrived three years ago, that’s gone completely. She wakes up, and she’s already running. No runway, no coffee buffer, no warm-up lap. Just immediately present, immediately on. It’s like a switch got flipped somewhere around the time she became a mother, and it hasn’t flipped back.

The Ximungwe female looks extremely alert and focused.

I find this fascinating, partly because I love her and partly because I recognise it. Not in myself, I still open my eyes, and I’m ready to go, which is its own kind of wiring, but because I’ve watched the same thing in the bush.

A leopard mother does not sleep the way she did before she had cubs. She can’t afford to.

One of them climbed on top of Mum and began chewing her ear.

Sleep, for most mammals, isn’t a single uniform state. It operates in cycles, moving between lighter stages and the deep, restorative slow-wave sleep where the real physical recovery happens, and REM sleep where the brain consolidates memory and processes the day. Humans need all of the above. We’re built for roughly 7 to 9 hours, cycling through all of it multiple times a night. Deprive us of the deep stages, and we function badly. Deprive us of REM, and we start to unravel fairly quickly.

A leopard doesn’t sleep the way we do under the best of circumstances. Cats, all cats, from the one on your couch to a leopard in a marula tree, are what you might call opportunistic, light-cycle sleepers. They rest frequently, sometimes up to sixteen or eighteen hours a day, but rarely in the sustained, deeply unconscious way humans need to function. The term “cat nap” exists for a reason. As both predator and prey, a leopard that genuinely switched off for hours at a stretch would be a leopard that didn’t survive very long. The baseline of a leopard is already alert. The ears are already moving independently of the rest of the body. One eye is already half open.

So a leopard mother isn’t making a dramatic departure from normal leopard sleep; she’s just running the same system under higher load, with the threat radius pulled in tighter around the den. What does shift, and this is well supported in mammalian research broadly, is acoustic sensitisation. A mother’s brain becomes specifically tuned to the sounds of her offspring, able to filter background noise that doesn’t matter and respond immediately to sounds that do. Her cubs shifting in the den, a distress call, something approaching that shouldn’t be. The brain doesn’t fully disengage from that frequency even during rest.
Which, when you think about it, is exactly what happened to Samantha.

Sound familiar, Sam?

Here’s where it gets interesting for me personally, because I used to think my heavy sleeping was just who I am. Turns out it’s also a function of threat perception. I sleep heavily at home because my brain, correctly, has assessed that the environment is low-risk. But the moment the threat calculus changes, so does the sleep.

I’ve been woken from a dead sleep by the sound of lions fighting over a carcass close to camp. Not gradually, but bolt upright, completely alert, heart already going before I’d consciously registered what I’d heard. But I will admit, this is not out of fear for what was going on, but purely out of excitement and the desire to get out there and see it. The same thing happened when the Flat Rock Male killed a bushbuck thirty metres from my bathroom window in the middle of the night. One second unconscious, the next second fully present and trying to work out exactly what I was hearing and how close it was. And any parent will tell you the same thing happens with their kids. I am a heavy sleeper in every conventional sense, but the sound of one of my children in the night has me awake before I’ve decided to be. Any slight noise from them, be it a cough, a moan or crying, I would hear across the house without fail, which I find slightly miraculous given I can apparently sleep through a small natural disaster.

The science behind this is actually well established. The brain doesn’t shut down uniformly during sleep, it continues to process sensory input and applies a kind of triage to incoming sounds. Familiar, low-threat sounds get filtered out. Novel or biologically significant sounds, a predator, a child in distress, something that doesn’t belong, bypass the filter and trigger arousal. A mother’s brain becomes particularly sensitised to the acoustic signature of her own offspring.

A leopard mother operates on the same principle, tuned to a higher pitch. The rustle of her cubs settling is background noise. The snap of a twig that doesn’t fit the pattern, the scent of a hyena nearby, these cut straight through whatever rest she’s managing to get.

Now consider Olli and Seb for a moment, because they are, without knowing it, running a fairly accurate demonstration of how sleep needs shift across development. I will just add that we are extremely grateful that our two kids still nap.

Olli at three is a chaos engine with unpredictable fuel requirements. Some days she sleeps for two hours at school from eleven, gets home on the bus at half two, crashes again in the afternoon, and is still a complete mess by seven in the evening. Other days, the school nap doesn’t happen, the afternoon nap doesn’t happen, and by six-thirty, she is operating on fumes and poor decisions. A three-year-old needs between ten and thirteen hours of sleep in a twenty-four-hour period, and the split between nighttime sleep and daytime naps is still negotiating itself. Her brain is undergoing extraordinary development, neural pruning, memory consolidation, and language acquisition, and sleep is doing a significant portion of the heavy lifting for all of it.

Seb at four and a half is closer to the other side of that transition. He still naps after school when the morning has been active enough to warrant it, but the nap is becoming optional rather than essential. His brain is consolidating. The sleep architecture is shifting toward what it will eventually look like in adulthood: longer consolidated night sleep, less dependence on daytime top-ups.
A leopard cub follows a remarkably similar arc. Very young cubs sleep in short, frequent bursts. Their brains are developing at a comparable rate and require the same kind of consolidation time. As they grow and their neural architecture matures, sleep patterns consolidate, and the vulnerability of frequent unconsciousness decreases. By the time a cub is approaching independence, it sleeps more like an adult leopard. Which, given the demands of a solitary hunting life, means opportunistically, lightly, and always with one metaphorical eye open.

The giraffe, for what it’s worth, manages the whole thing on around thirty minutes a day. I have written about this before, and I remain personally offended by it.
What strikes me most, thinking about all of this, is that Samantha’s transformation from slow-morning-person to immediately-operational-upon-waking isn’t a personality change. It’s a biological one. Motherhood restructured her sleep in the same way it restructures a leopard mother’s sleep. Not because she decided to be more alert, but because her brain recalibrated around what the environment now required of her. The threat isn’t lions. It’s a three-year-old who thinks six in the morning is a perfectly reasonable time to be having a conversation about dinosaurs.

The adaptation is the same. The predators are just different.

I shared this theory with Sam over dinner recently. She listened, nodded slowly, and then asked if I was really comparing her to a leopard in a blog that people were going to read.

I told her the leopard was the compliment.

She seemed cautiously willing to accept that.