Migration patterns and diurnal use of shelter in a ranid frog of a West African savannah: a telemetric study

Abstract

Abstract A telemetric study on Hoplobatrachus occipitalis (Anura: Ranidae) was conducted in the Comoé National Park (Ivory Coast, West Africa) from 1993 to 1995 during the beginning of the rainy seasons. Radio transmitters were implanted into 46 frogs. The locations of individual animals were tracked for 2 to 71 days, at least once per day and once per night. By day, the frogs were found in diurnal shelters that offered favorable temperature and humidity conditions as well as protection against predators. At night, with the beginning of the rainy season, both males and females occupied about equally large home ranges of on average 142 m2 (range: 23-3744 m2) in a partially dried-up river bed. Individuals with home ranges on rocky stretches along the river weighed significantly less (35 ± 9 g) and occupied significantly larger home ranges (median: 944 m2) than did individuals found in places along the river having dense and shady vegetation (median of home range: 45 m2, body weight: 66 ± 21 g). Frogs migrated when precipitation was above 15 mm per day (movement >30 m per animal and day). Movement over longer distance (>600 m per animal and day) took place only once a year, when the first heavy rainfall of the season filled the dried-up ponds in the savannah. On these longer migrations, nearly all radio-tracked frogs moved from the river to newly emerged ponds in the savannah, covering linear distances of up to 1.4 km in a single night. The frogs then stayed in the savannah and most of them repeatedly sought new breeding sites during the rainy season. Thus, the total space covered by the frogs, termed "activity area", amounted to up to 2 km2, for both sexes, during the observation period.