The "H" in "hibou" is an H aspiré or aspirated H. It is silent, but treated as a consonant when it comes to elisions. So l'hibou is not allowed. Other aspirated H words are "le heros" (hero) and "le haricot" (bean).
The opposite is the H muet or mute H. Also silent, but elisions are mandatory. For example, "l'homme."
The "h" in Old French was originally pronounced. Then it became silent and was replaced by liaison. Then an influx of Germanic words were added to the language, which brought "h" back. Then these new "h"s became silent as well but did not get liaised!
The original Vulgar Latin/Old French "h"s are now "h" muet, and the newer Germanic "h"s are "h" aspiré. That's why different words follow different rules. Unless you're really interested in the etymology of each word, it's best to just remember the words individually.
Most aspirated-h words are derived from Germanic languages. L'hibou is one of many exceptions. It is thought to be onomatopoeic. Ie. A word that imitates the call of the animal. Maybe that's why the pronunciation of the 'h' has endured.
Historically, yes, but in modern French, there is often no difference. I found this extremely clear video which explains why: https://www.youtube.com/watch?v=DYnIuVcKTHA (note that "de" traditionally has a [ə] schwa or mute-e sound, while "deux" has a [ø] sound)
Here is a written explanation: https://en.wikipedia.org/wiki/French_phonology#Schwa
Like the previous comment said, "de" should be a schwa and "deux" should be a slashed o (ø). Though the IPA on Wiktionary doesn't support it, I think there should also be a difference in stress, with de being unstressed (the noun is the focus) and deux being a slightly longer vowel.
Quite wonderful! The female owl is la chouette, while the male owl is le hibou. Who knew? More importantly, who knows besides the owls? I learned this reading Harry Potter in translation, and owls, m and f, figure prominently among the magical. Harry's Hedwig, a snowy owl, is la. Good place to go, a lot of colloquial conversation at about an 11 year old level.
That is not correct, sorry. They are different animals. Les hiboux ont des aigrettes de plumes sur la tête. (They have tufts of soft hair that look like ears on their heads.) Les chouettes, such as the barn owls, don't have them. I believe what you are referring to is simply the gender of the words in French.
There are two words for owl in French, corresponding to two kinds of owls. "Un hibou" et "une chouette". The Duolingo mascot has egrets on his head, so he's un hibou.
The articles in front of body parts depends a lot on the sentence construction. The sentence above is merely about possession. So "has large eyes" is different from "has the large eyes".
On the other hand, there are sentences that involve reflexive verbs, and those generally involve definite articles with body parts. For example, "Mon chien s'est essuyé les pattes". (My dog wiped his feet.)