在电线杆上 / 多嘴。
you cant put 上and 多嘴 together here.
上 is not on. "on" should be tranlated into "在......上" here.
在电线杆上，you see, we have to say “在 something 上”, instead of "在 sth" when we express sth is on sth.
some sparrows, they were out of the window, and they were on the/a telegraph pole/wire pole/telephone pole/wirepole, these sparrows were chattering/chirpping/twittering.
in my opinion,叽叽喳喳 is better than 多嘴 here.