I don't know of any specific studies that have been done relevant to dangers of new and/or
used automotive tires present to companion birds, however, there have been recent (within the last 10 years)
done on the safety of chopped up tires for use in children's playgrounds and the following chemicals and substances were
found to be present in this/these chopped up rubber/tires...and although the studies were primarily concerned with
inhaliation of substances, many of the following substances/items are deadly to companion birds, in their own right,
let alone mixed with other substances:
acetone, aniline, arsenic, barium, benzene,benzothiazole, cadmium,
chloroethane, chromium, cobalt, copper, halogenated flame retardants,
isoprene, latex, lead, manganese, mercury, methyl ethyl ketone,
methyl isobutyl ketone, naphthalene, nickel, nylon, phenol, pigments,
polycyclic aromatic hydrocarbons, polyester, rayon,styrene‑butadiene,
toluene, trichloroethylene
For further information, take a look at:
Tire Crumbs | Featured News | Exposure Research | US EPA
I think I would find other, safer ways of disposing of or otherwise utilizing a
garage full of used and/or new tires.....