Seasonal variation in thyroxine in the American alligator (Alligator mississippiensis)

Male and female alligators ranging from 58 cm to 361 cm in length (N=1054) were captured and their blood was sampled between 9 A.M. and midnight from June 2000 - June 2002 at the Rockefeller Wildlife Refuge in Grand Chenier, LA. Animals were captured in a variety of habitats including marsh, open water, canals, and ponds. Total thyroid hormones were measured by radioimmunoassay. Four criteria were used to evaluate changes in hormone levels: sex, total length, season, and time of day. Thyroxine (T4) varied over a wide range from 0.5 to 57 ng/mL. Triiodothyronine (T3) levels were below the sensitivity of the assay (