Son just sent a video of hummingbird pups in a nest. Their beaks look like many bird beaks - triangular, essentially. How do they develop into the long, hollow tubes we see in adults? Do they actually shed them? What happens? Colibri - you still here?
They simply grow longer, like other baby bird’s beaks.
The beaks of adult hummingbirds aren’t “hollow tubes.” They can open their beaks like other birds. They don’t suck nectar up like through a straw, but lap it up with extensible tongues.
“Pups” ?
Just an expression.
Everyone knows a baby hummingbird is called a “joey” 
Pretty sure they’re called ‘calves’
Lots of animals start out significantly different as young than they end up as adukts.’
Look at collie dogs (‘Lassie’), and the long nose. As pups, they have much flatter faces – they have to be able to nurse from the mother. Their noses grow long as they grow up.
In cattle, the calves don’t have horns while young – it would make nursing very uncomfortable. In fact, most mammal species are born without teeth for the same reason – to make it easier to nurse without damaging the teat. Often the development of teeth is timed to match the weaning of the youngster from nursing onto regular food.
I have been able to observe the development of hummer baby beaks for the last 2 years. Up until about a week before leaving the nest, their beaks are very much like regular beaks. The mother feeds them like a regular bird. But about a week before they leave the nest, their beaks undergo rapid elongation. During this time they also perch on the nest rim and practice exercising their wings. As far as I can tell, after they leave the nest, they remain in close proximity, and the mother will find them, visit and feed them.
This is just based on casual observation, and should not be considered to be authoritative as it is based on infrequent casual data.
I think a more graphic example are greyhounds. They start out looking like any other dog pup and around 16 weeks old the legs, spine and face get a huge growth spurt [pic of pups in the middle of this growth stage].
![[pic of pups in the middle of this growth stage]](https://www.grv.org.au/wp-content/uploads/2014/04/BuyingPup01.jpg){kind=link}
You know how hummingbirds go into torpor (hibernate) every night. Wonder if the babies do that too or their bodies are not mature enough for that ?
Hummingbirds don’t go into torpor every night, just when temperatures are low. The female needs to incubate the eggs and nestlings at night so she can’t go into torpor. The nestlings at first can’t control their own body temperature so they get the heat they need from their mother.