Durante el avistamiento vimos una bandada con los prismáticos.

Durante means during and is followed by a noun phrase, here el avistamiento.

• durante el avistamiento = during the sighting / during the observation

By contrast, mientras usually introduces a clause with a verb:

• mientras observábamos = while we were observing

So durante is correct because what follows is a noun phrase, not a full clause.

In Spanish, abstract or event nouns often appear with the definite article where English might omit it.

So:

• durante el avistamiento sounds natural
• durante avistamiento sounds incomplete or unnatural

The article el helps present avistamiento as a specific event or activity already understood in the context.

Avistamiento is a noun from avistar, meaning to sight or to spot, especially at a distance.

Depending on context, it can mean:

• a sighting
• an observation session
• a spotting event

In nature or birdwatching contexts, avistamiento is very common, as in:

• avistamiento de aves = birdwatching / bird sighting
• avistamiento de ballenas = whale watching

So it sounds quite natural in a wildlife or observation context.

Vimos is the preterite of ver, and it presents the action as a completed event:

• vimos una bandada = we saw a flock

Veíamos is the imperfect, which would suggest an ongoing, repeated, or background action:

• veíamos una bandada could mean we were seeing a flock or we used to see a flock, depending on context

In this sentence, vimos is the natural choice because it refers to one completed sighting during that event.

Spanish usually drops subject pronouns when the verb form already makes the subject clear.

• vimos already means we saw

So nosotros is unnecessary unless you want emphasis, contrast, or clarification.

For example:

• Vimos una bandada = neutral
• Nosotros vimos una bandada = we saw a flock, as opposed to someone else

Bandada usually means a flock, especially of birds.

It refers to a group moving together, often in flight.

Common related words:

• bandada de pájaros = flock of birds
• rebaño = herd/flock, usually for sheep
• manada = pack/herd, often for mammals
• cardumen = school of fish

Because the sentence uses avistamiento and prismáticos, bandada strongly suggests birds.

Spanish normally uses an article with countable singular nouns when introducing one item.

• una bandada = a flock

Leaving out the article would generally be ungrammatical here.

Spanish does sometimes omit articles in special contexts, but after ver with a singular count noun, you would normally need one:

• vimos una bandada
• not vimos bandada

Yes, technically it could look ambiguous at first, because con + noun can attach to different parts of a sentence.

But in normal interpretation, con los prismáticos modifies the verb vimos:

• we saw a flock with the binoculars

It does not naturally mean that the flock had the binoculars. That reading is grammatically possible in theory but absurd in context, so native speakers automatically understand the intended meaning.

If you wanted to make the instrument reading even clearer, you could also say:

• Durante el avistamiento, vimos una bandada usando los prismáticos
• Durante el avistamiento, con los prismáticos vimos una bandada

Spanish often uses the definite article with everyday objects, especially when the reference is clear from context.

So con los prismáticos can naturally mean:

• with the binoculars
• with our binoculars
• with the binoculars we were using

English often prefers a possessive, but Spanish does not always need one.

Compare:

• Me lavé las manos = I washed my hands
• Vimos la bandada con los prismáticos = We saw the flock with the binoculars

If you want to stress ownership, you can say:

• con nuestros prismáticos

But the original sentence is completely normal.

Yes. In Spain, prismáticos is very common for binoculars.

In many parts of Latin America, people may more often say:

• binoculares

Both are understood, but prismáticos sounds especially natural in Peninsular Spanish, which fits your Spanish (Spain) focus.

Yes. Spanish word order is more flexible than English, though some versions sound more natural than others.

Original:

• Durante el avistamiento vimos una bandada con los prismáticos.

Other possible versions:

• Vimos una bandada con los prismáticos durante el avistamiento.
• Durante el avistamiento, con los prismáticos vimos una bandada.

The original sentence is perfectly natural. Changing the order usually affects emphasis rather than basic meaning.

The original sentence is correct and natural, especially in a nature-watching context. But in more casual speech, a speaker might choose slightly simpler wording, such as:

• Durante la observación vimos una bandada con los prismáticos.
• Mientras estábamos observando, vimos una bandada con los prismáticos.

So the original is fine, but avistamiento has a slightly more specialised or descriptive feel than very basic everyday speech.