A suggestion on how to weigh "chickens on the fly".

Design a simple feeding station that will allow
only one bird to feed at each port at a time.
Place a simple scale at each port and log the
time of day to the millisecond and weight each
time a chicken feeds.

For a sample of 100 chickens it would require
twenty feeding stations with five ports each.

The stations would be placed in the barn separated
by a large enough distance so that one bird could not
feed at more than one port in a few seconds.

Leave the stations in place to 20 to 30 minutes then
collect the data. 100 samples with time stamps in the
same 500 millisecond will be found and the average
will reflect the population.

Charles.