Når jeg ser fuglen ved reden og kaninen i græsset samtidig, føles haven mere levende end før.

Yes. Når here means when in the sense of whenever / at the times that.

In this sentence, Når jeg ser fuglen ved reden og kaninen i græsset samtidig means something like:

• When(ever) I see the bird by the nest and the rabbit in the grass at the same time

A useful contrast is:

• når = when / whenever for something general, repeated, or expected
• da = when for a specific event in the past

So når is the natural choice here because the sentence describes a general situation, not one single past event.

Because the sentence begins with a subordinate clause:

• Når jeg ser fuglen ved reden og kaninen i græsset samtidig

Then the main clause starts:

• føles haven mere levende end før

In standard Danish writing, a subordinate clause is separated from the main clause with a comma. So the comma marks the boundary between the when-clause and the main statement.

This is because of Danish V2 word order in main clauses.

When something comes before the main clause—here, the whole subordinate clause beginning with når—the finite verb in the main clause must come in second position.

So the structure is:

• Når ... , føles haven ...

not

• Når ... , haven føles ...

This is very common in Danish:

• I dag kommer han.
• Når jeg har tid, læser jeg.
• Hvis det regner, bliver vi hjemme.

So after the fronted clause, Danish puts the verb first in the main clause, then the subject.

In Danish, føles often means feels in the sense of seems / gives the impression of feeling.

So:

• Haven føles mere levende = The garden feels more alive

This is similar to English, where we can say:

• The room feels cold
• The city feels different at night

It does not mean the garden literally has feelings. It describes the speaker’s impression of the garden.

Also, føles is the usual form here; haven føler sig... would mean something like the garden feels itself..., which does not work in this context.

Danish often uses the definite form where English might use the.

These are all definite forms made with the Danish definite ending:

• fugl → fuglen = the bird
• rede → reden = the nest
• kanin → kaninen = the rabbit
• græs → græsset = the grass
• have → haven = the garden

This suggests the speaker has a particular bird, nest, rabbit, patch of grass, and garden in mind—probably ones already known from the context or the situation.

You usually remove the definite ending:

• fuglen → fugl
• reden → rede
• kaninen → kanin
• haven → have

For neuter nouns, the definite ending is often -et, but spelling can change slightly:

• græs → græsset

So the common singular pattern is:

• common gender noun: en fugl → fuglen
• neuter noun: et græs?
  Here, be careful: græs is normally an uncountable noun, but the definite form is still græsset = the grass

Because ved means by / near / next to, while i means in.

So:

• ved reden = by the nest
• i reden = in the nest

The sentence says the bird is by the nest, not necessarily inside it. That is why ved is used.

This is a very natural distinction in Danish:

• ved bordet = by the table
• i huset = in the house

I græsset means in the grass.

Here, i is natural because the rabbit is imagined as being among or within the grass. Danish uses i in many of the same situations as English in:

• i haven = in the garden
• i vandet = in the water
• i græsset = in the grass

So the contrast is:

• ved reden = by the nest
• i græsset = in the grass

No, it does not need to be repeated. Danish can coordinate two objects after one verb, just like English:

• jeg ser fuglen ... og kaninen ...

This means:

• I see the bird ... and the rabbit ...

The verb ser applies to both nouns:

• I see the bird by the nest
• and the rabbit in the grass

You could repeat the verb for emphasis or clarity in some contexts, but it is not necessary here.

Samtidig means simultaneously / at the same time.

Here it tells us that the speaker sees both things at the same time:

• the bird by the nest
• and the rabbit in the grass

So samtidig applies to the whole seeing situation, not just to græsset or kaninen.

A natural paraphrase would be:

• Når jeg samtidig ser fuglen ved reden og kaninen i græsset...
• Når jeg ser både fuglen ved reden og kaninen i græsset på samme tid...

All of these express the same basic idea.

Because levende is usually compared with mere in ordinary modern Danish:

• levende = alive / lively / vivid
• mere levende = more alive / livelier / more vivid

This works like English more + adjective.

Danish does have many adjectives with an -ere comparative, such as:

• stor → større
• gammel → ældre

But not every adjective normally forms the comparative that way in everyday use. With levende, mere levende is the natural choice.

Not literally, no. Here levende means something closer to:

• alive
• lively
• full of life
• vivid

So haven mere levende means the garden seems more full of life, more active, more vibrant.

That fits the image: seeing both a bird and a rabbit makes the garden feel richer and more animated.

End means than, and før means before.

So:

• mere levende end før = more alive than before

Here før is not attached to a specific time word like before now, but the meaning is understood from context: the garden feels more alive than it did previously.

Yes. Danish often uses både ... og to emphasize both ... and.

For example:

• Når jeg ser både fuglen ved reden og kaninen i græsset samtidig, føles haven mere levende end før.

That would be perfectly natural too. The version without både is also correct; it is just slightly less explicitly emphatic.

Yes. In the main clause:

• føles haven mere levende end før

the subject is haven.

You can tell because haven is the thing that feels more alive. It appears after the verb only because Danish main clauses follow V2 word order when another element has been placed first.

So the underlying meaning is:

• Haven føles mere levende end før

But after the initial når-clause, it becomes:

• Når ..., føles haven mere levende end før.