It shouldn't, but who knows. It's main ingredient, MPCA, has shown low-to-moderate any toxic affect to avians. I've very rarely used that stuff, and only on a front boulevard.
I've noticed a big drop in birds here, too. I think in the Summer there's so many areas with water/shelter/food etc, they tend to move around a lot more. Loss of habitat, trees, fields, etc certainly make a hug difference. This town is hell-bent on turning the place into a shiny concrete and steel glitter dome, thanks to Mayo, and lots of fields and meadows out near me have disappeared. Too many new housing developments springing up can't be good for birds.
I've also had two Cooper's hawks move in and raise a brood...that drove a lot of birds out, and they killed a lot of songbirds, since that is their main diet.
Environmental Health Effects
Although insoluble in water, MCPA can have a high mobility in soil. MCPA can negatively affect the growth of some crops, including onion, cabbage, lettuce, and turnip (#EPA).
In mammals, MCPA generally has a low toxicity, and is rapidly excreted. The oral LD50 in rats is 765 mg/kg. The dermal LD50 exceeds 2000 mg/kg, and the inhalation LC50 exceeds 6.3 mg/L (#EPA).
MCPA has a moderate to low toxicity to birds. The oral LC50 is 377 mg/kg in bobwhite quail (#EPA). It is practically non-toxic to honey bees with an LD50 of 104 ug/bee. MCPA is slightly toxic to freshwater fish, and mostly non-toxic to other aquatic organisms. The LC50 of rainbow trout ranges from 117 mg/L to 232 mg/L (#EXTOXNET).
MCPA is a General Use Pesticide, although all product labels are required to carry the signal word "danger" because it is a severe eye irritant (#EXTOXNET).