Is canary poisoning rate caped?

[Mday]

I was trying to mass produce some feathers for darts. Build like 40 bird cage and caught 40 birds on the same day. Instead of getting 40 poisoned birds within the next 3~5 days, I am getting like 2~3 poisoned bird per day. Is there a cap on the poisoning rate? Feel so weird to see some birds sitting there for so long and were still in a queue waiting for toad's poisonous gas to be distributed.

[zzKratoszz]

From my limited knowledge on reading code this is what I found. 

Spoiler

inst:ListenForEvent("birdpoisoned", function(world, data)
                if data.bird ~= inst then
                    inst._gaslevel = math.min(inst._gaslevel, math.random(6) - 1)

I didn't take the time to read what the bolded line means because I am code illiterate, but the gaslevel has to be greater than 12 to poison a bird. This line resets the gas level every time a bird is poisoned, as far as I can tell. Its also only a chance to poison a bird which explains why only a couple birds are poisoned if this number resets to below 12.