Relationship between gonadal steroids and corticosterone during blood sampling in saker falcons

Blood sampling in manually restrained or ketamine (15 mg/kg given intramuscularly) treated saker falcons (Falco cherrug) induced an increased concentration in plasma corticosterone. Elevated plasma progesterone, oestradiol 17 beta, and testosterone concentrations also were observed in some of these birds. An inverse relationship was demonstrated between levels of corticosterone and progesterone, but not with the levels of other hormones. It is suggested that progesterone measurement should be taken into consideration when studying the influence of stressors in falcons.