The pharmacokinetics of OPEs in wildlife is extremely limited, even though OPEs are being manufactured and used in products at record-high levels, and have been shown to cause numerous deleterious effects. This thesis aims to analyze the behaviour of OPEs in an avian model, the herring gull (Larus argentatus) and their eggs, with an emphasis placed on understanding OPE accumulation and metabolism in the body. Herring gull eggs were collected over a 20 year span from multiple sites across the Great Lakes. OPE profiles varied slightly between colony sites and collection years, although at all sites only tris(2-chloroisopropyl) phosphate (TCIPP), tris(2-chloroethyl) phosphate (TCEP), tris(2-butoxyethyl) phosphate (TBOEP) and triphenyl phosphate (TPHP) were detected. In general, ΣOPE concentrations in 2010 were significantly higher (p < 0.05) than they were between 1990 and 2004. In a preliminary food web study, only TBOEP was consistently detected among multiple fish species from the Great Lakes, and showed weak biomagnification in the aquatic food web. OPE distribution among eight tissues in maternal gulls and their eggs showed that OPEs accumulate most in fat, followed by egg yolk ≈ egg albumen, whereas OPEs were not detectable in liver, and brain. In the first study of its kind, OP diesters were detected and quantified in herring gull plasma, indicating OP triester metabolism in vivo. The rate of metabolism of six OP triesters was assessed in herring gull liver microsomes. Tri-n-butyl phosphate (TNBP) was metabolized the fastest, followed by TBOEP, TCIPP, TPHP, and finally tris(1,3-dichloro-2-propyl) phosphate (TDCIPP). Triethyl phosphate (TEP) was not metabolized, regardless of administered concentration. Biotransformation of OP triesters to diesters varied greatly between compounds, with up to 10-fold differences between OP triesters. In general, structure-dependent biotransformation differences were observed, with halogenated alkyl triesters being transformed to their respective diesters more-so than non-halogenated alkyl triesters. It is evident that OP triesters are, in many cases, rapidly metabolized in vivo, and thus OPE concentrations observed in tissues samples represent post-metabolic residues. This thesis is critical in understanding the pharmacokinetics of OPEs in an avian species, and emphasizes the importance of identifying and monitoring OPE metabolite concentrations in biota.