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."
So is there a rule to follow that tells you when and when not to use an elision or do you just have to memorize the words?
No rule. You must look up the H word whether it’s muet or aspiré.
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.
By audio only, is there a difference between "de grands yeux" and "deux grands yeux"? I can't hear any difference. Any help to distinguish the two would be appreciated.
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
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.
He is le hibou, while she is la chouette. How do you tell owls apart, who have next to no sexual dimorphism?
On the question immediately preceding this one, DL would not accept grand for large. Yet here it uses grands for large. Totally inconsistent.
It depends a lot on the context because "grand" does not always mean "large". So yes, there could be inconsistency because this is not a one-to-one translation.
Indefinite article (du/de la/des) becomes just "de" when the adjective precedes the noun.