This is the 8919th most frequent Russian word.
птицу
"Птицу" is the accusative singular form of "птица," which means "bird" in English.
Here, 'птицу' is used in the accusative case to indicate the direct object of the verb 'вижу'.
Я вижу птицу.
I see a bird.
In this example, 'птицу' again appears in the accusative case, describing the specific bird that is being studied.
Учёные изучают птицу в лаборатории.
Scientists study the bird in the laboratory.
The word 'птицу' acts as the direct object of the verb 'поймали', showing the bird as the thing caught.