Most of the toxicological research in the oil sands region has focused on aquatic contaminants with little attention being given to air contaminants. Therefore, we conducted experimental and field studies on birds. Captive Japanese quail (control, low, and high dose groups; n=12/group) and American kestrels (control and exposed; n=10/group) were exposed experimentally through inhalation, to mixtures of benzene, toluene, nitrogen dioxide (NO2), and sulfur dioxide (SO2) for 1.5 hrs/day, 5 days/week for 4 weeks. In addition, nest boxes for tree swallows were erected at two oil sands sites and a reference site, passive air monitors were set up underneath and behind the boxes. Air contaminants were higher at the oil sands sites for NO2, SO2, volatile organic compounds (VOCs), and polycyclic aromatic compounds (PACs) (> 5fold). The tree swallow nestlings had a decreased T cell response (p=0.007), whereas the quail and kestrels had no differences in the B or T cell immune responses (p>0.5). The bursa of Fabricius was smaller in the swallow nestlings (p<0.02) only. There were no histological alterations in the bursa of Fabricius and the spleen (p>0.05) for any of the three species studied. Plasma corticosterone in quail displayed a hormetic response (higher levels in low than in high group), and the exposed kestrels had higher levels than controls (p = 0.007). Feather corticosterone was similar among nestlings (p>0.6). Free and total thyroxine was lower in exposed kestrels than in controls (p= 0.001 and p=0.004). Hepatic cytochrome P450 measured by the 7-ethoxyresorufin-O-dealkylase (EROD) assay was induced in kestrels (p=0.02) but not in quail (p=0.43). Compared to the reference nestlings, birds from the industrial sites had greater hepatic EROD induction (p<0.0001) with decreased hepatic mass (p=0.0001). In these studies we show evidence of biological costs associated with exposure to air contaminants; however, the birds appear to compensate successfully. For the first time, we demonstrate hepatic EROD induction from exposure to air contaminants. We suggest that birds residing in the oil sands region are valuable sentinels of environmental health and are good models for studying the long-term impacts of contaminants from the oil sands on biota.