Hmmm... Your numbers are all off. Consider these two statements from your article:

"the worker picks up 150 gallons of pigeon dung annually" 
"One pigeon can produce 25 pounds of guano per year"

1 gallon of water weighs 8 pounds.
I gallon of feces weighs between 1 and 4 pounds, depending on the water content.

Lets take the high end of this ratio, and we'll use the weight of water in this measurement:

150 (gallons) x 8 (lbs) = 1200 lbs

1200 (lbs) ÷ 25 (lbs of guano p/year, p/bird) = 48 (birds)

So, you are telling me that Fairbanks has about 48 pigeons... or you are inflating the production of guano.

Since I own a pet pigeon, I'd have to say the latter. My pigeon doesn't have scrounge for food, and gets to eat as much as she wants. She has never pooped that quantitiy in a year's time. Her fecal matter amounts to a couple of ounces per week - less that 8 pounds per year, which is a lot less than one homeless junkie excretes on your side-walks in a week... or a huskie, or a bear...