Утром на подоконник сел воробей.

In the morning, a sparrow landed on the windowsill.

Breakdown of Утром на подоконник сел воробей.

• на: on
• утром: in the morning
• подоконник: the windowsill
• сесть: to land

Questions & Answers about Утром на подоконник сел воробей.

Why is утром used here, and what case is it?

Утром is the instrumental singular form of утро (morning).

In Russian, some time expressions use the instrumental case in an adverb-like way. So:

• утром = in the morning
• вечером = in the evening
• днём = during the day / in the daytime

So even though утро is a noun, утром functions almost like an adverb here.

Why is it на подоконник, not на подоконнике?

Because this sentence describes movement toward a place, not being located there already.

With на:

• на + accusative = motion onto something
• на + prepositional = location on something

So:

• сел на подоконник = sat down onto / landed on the windowsill
• сидел на подоконнике = was sitting on the windowsill

Here the sparrow moves to the windowsill, so Russian uses подоконник in the accusative: на подоконник.

Why is the verb сел used instead of сидел?