Lovely little sciency details from Httyd is how there's a variety of dragon species according to climate and habitat.
There's a bunch of dragons in the Book of Dragons but many of them are uncommon on Berk and some even reside far off. I recall Hiccup reading about thunderdrums being reclusive and residing in tidepools.
Whispering deaths are more common near Outcast Island and mostly Islands which are barren and much too rocky. And in rtte, the further they go from Berk, the more variety the gang encounters, all according to their habitats. They see some dragons for the very first time even though they've read about them in the book of dragons.
The whole zoological geography of it is wonderful. Deep sea dwellers, shallow water dwellers, cave dwellers, pack dragons, nesting dragons, territorial ones etc. They all exist but reside in places spread out and away. Places which are ideal for them. Amazing world building I tell you.
Every species lives in its ideal climate and habitat and they're not all found in one place, rarely ever. Berk's local dragons are usually the species the gang has and I noticed how these particular species were a lot more common in Dragon's Nest as depicted in first movie but not so much in Bewilderbeast's sanctuary, that has a completely different variety of dragon species.
A species not common to Berkian air and waters being seen there was peculiar or came as a surprise in many cases. And I loved the moments where the gang went: "this dragon which resides in a different habitat? What's it doing so far out here? Something must be up."
Love how most of these dragons had their own separate habitats and islands that weren't Berk or islands close to it (a radius of which mainly included the common species spread out from epicenter of Dragon Island [previously Red Death's nest]). It's even possible to map the different kinds of dragons according to their respective territories over the archipelago and beyond.
Love that the httyd universe is more inclined towards science than fantasy when it comes to dragons.