This is the 17615th most frequent Russian word.
тысячами
"Тысячами" means "by thousands" or "in thousands."
Here, 'тысячами' describes the approximate number of people gathering.
Люди тысячами собираются на площади.
People gather by the thousands in the square.
In this context, 'тысячами' refers to the units of monetary calculation.
Продавец подсчитал выручку тысячами.
The seller calculated revenue in thousands.
'Тысячами' in this sentence conveys the quantity of birds traveling to a location.