That's practically the weight of a small car,

but it's the typical size of a newborn blue whale,

the biggest baby in the animal kingdom.

When they nurse, calves put on 90 kilograms

every single day

thanks to their mom's extremely rich milk,

which contains over 10 times more fat than cow milk.

So calves can grow to the size of a Boeing 757 by adulthood.

Sounds like a pretty cushy start to life,

especially when compared to other hefty newborns.

On dry land, elephants win the biggest-baby award,

though winning is a relative term.

They give birth to a 105-kilogram calf,

which first had to gestate in mom's womb

for nearly two years,

more than twice as long as a human pregnancy!

Close behind elephants are giraffes.

They drop a 75-kilogram calf, on average.

Literally. Mom gives birth standing up,

so the baby falls almost 2 meters to the hard ground.

But it turns out that tumble is pretty important.

The impact breaks open the amniotic sac,

allowing them to take their first breath of air.

Next in line is the white rhino.

Although not quite as long a pregnancy as an elephant,

babies still gestate for 15 to 16 months.

Once they're finally born,

calves weigh 40 to 64 kilograms,

roughly the size of an adult Saint Bernard.

But here's the thing. If you're about to give birth,

you're not actually worried about your kid's size.

You're worried about their size compared to you.

And shingleback lizards have it bad. Really bad.

Unlike most reptiles, they give birth to live young.

Usually, twins that total a third of their body weight.

That's like a human giving birth to a 7-year-old.

Meanwhile, bats usually have just one baby at a time.

But that one pup is huge!

A fourth of their mother's body weight.

That's equivalent to a human infant

the size of a 16-kilogram cocker spaniel.

Meanwhile, horse foals usually are 1/10

of their mother's size.

That's a bowling-ball-sized baby, in human terms.

Speaking of humans,

our newborns weigh about 3.5 kilograms on average.

Or 1/22 of mom's size.

That might not sound like much,

but we're actually pretty big.

After all, tiger cubs weigh only 1/120

of their mother's size,

and a red kangaroo baby

is a minuscule 1/100,000

of mom's body weight!

That's right.

A newborn joey can be as small as a single grain of rice

and won't be ready to venture from the pouch

for over a year.

But the world's smallest babies

are a story for another time.