Observamos el buitre y el búho.

Because Spanish usually leaves subject pronouns out when the verb already makes the subject clear.

Observamos tells you the subject is we:

• observ-o = I observe
• observ-as = you observe
• observ-a = he/she observes
• observ-amos = we observe / we observed

So Observamos el buitre y el búho is completely natural without nosotros. You could say Nosotros observamos el buitre y el búho, but that normally adds emphasis, contrast, or clarification.

It can mean either one.

For -ar verbs, the nosotros form is the same in:

• the present: we observe
• the preterite: we observed

So observamos can mean:

• we observe
• we are observing (in some contexts)
• we observed

Context tells you which one is meant. If the sentence appears by itself, it is grammatically ambiguous.

In Spanish, it is normal to repeat the article before each singular noun in a phrase like this.

So:

• el buitre y el búho = natural
• el buitre y búho = usually sounds incomplete or unnatural

Spanish treats each noun as needing its own article here. English often lets one the cover both nouns, but Spanish usually repeats it.

That is also possible, depending on the nuance.

With people, the personal a is normally required:

• Vemos al profesor.

With animals, it is less automatic. Speakers often use a when the animal is:

• specific and individual
• emotionally important
• personified
• a pet, named animal, etc.

Without a, the sentence can sound more neutral or descriptive, as if you are simply observing animals as creatures or specimens.

So both can work:

• Observamos el buitre y el búho. → neutral/descriptive
• Observamos al buitre y al búho. → more individualized

Because they are pronounced differently internally.

• buitre has a diphthong: bui-tre
• búho has a hiatus: bú-ho

The accent mark in búho shows that the ú is stressed and forms a separate syllable from the o, even though there is an h in between. The h is silent and does not stop that vowel relationship for accent purposes.

So:

• buitre = 2 syllables
• búho = 2 syllables, but with a clear break between ú and o

A good approximate pronunciation is:

• buitre ≈ BWEE-treh
• búho ≈ BOO-oh

A few useful details:

• The h in búho is silent.
• The y in y el búho is pronounced like ee.
• The b and v sounds are not strongly distinguished in standard Spanish, so buitre does not have an English-style v sound.
• The r in buitre is a light Spanish tap, not an English r.

So the whole sentence is roughly: ob-ser-VA-mos el BWEE-treh ee el BOO-oh

Yes. In this sentence, both are masculine:

• el buitre
• el búho

This is grammatical gender, which does not always match biological sex. If you are just naming the species or referring to an animal in general, you normally use the standard noun gender.

If you need to specify sex, Spanish often adds words like:

• macho
• hembra

For example:

• el búho macho
• el búho hembra

Yes, but the meaning changes.

• el buitre y el búho = the vulture and the owl
  → specific ones, known from context

• un buitre y un búho = a vulture and an owl
  → not previously identified; just one of each

So the article choice depends on whether the animals are definite or indefinite.

Yes. That would mean We observe vultures and owls in a more general sense.

Compare:

• Observamos el buitre y el búho. → specific animals
• Observamos un buitre y un búho. → one vulture and one owl, not yet identified
• Observamos buitres y búhos. → vultures and owls in general, or several of them

So Spanish changes the article pattern depending on how specific or general you want to be.