Okay first off 635000 kilos is approximately 1399935 pounds or 700 US tons.
There's no way that bridge could support the extra weight.
and
How did they weigh all that poop?
I call bullshit
They very carefully removed it, one small sample at a time and weighed it on a reefer scale. How else do you think they could manage to spend $800,000 on pigeon shit?