Seasonal Thermoregulation in Nile Crocodile

Abstract

Thermoregulation data for four ‘problem’ Nile crocodiles ( Crocodylus niloticus ) introduced to Lake Ngezi, Zimbabwe in 1986-87 are presented. Data were collected from winter through early summer using abdominally implanted radio-transmitters with calibrated thermistors. These remain after 36 years the largest (1.94-3.48 m) wild free-ranging Nile crocodiles thus far evaluated re: thermoregulation and body temperatures. Both cooling and heating rates were highest in the smallest subjects, progressively lower in larger individuals. Body temperatures (T b ’s) cooled at night, but remained above or equal to water temperatures (T w ). All T bmax ’s exceeded maximum air temperatures (T a ) during daytime with the highest recorded T b being 36.4 o C. Daily T b amplitude’s of > 10 o C were routinely exhibited in all specimens. Both T bmax and T bmin generally lagged T amax ’s and T amin ’s by about two hours, respectively. The mean T b ’s increased seasonally from June through October for each individual.

Keywords: thermoregulation, body temperature, Nile crocodile