Terrestrial Activity of Caiman in the Pantanal, Brazil

Coordinated terrestrial movement has not previously been reported in crocodilians. However, between 1989 and 1999, 94% of 525 Caiman crocodilus yacare found on land in the Pantanal were in coordinated groups (n = 73) walking head to tail and forming nearly straight lines. Caimans left pools and initiated terrestrial movements spontaneously and in response to disturbance by researchers and hunters. The sex ratio of the groups was biased toward males (0.8 ± 0.24) and was similar to that found in aquatic habitats in the study area. However, two groups consisted only of females. When caimans left pools subjected to disturbances, such as hunting and capture for research, they walked head to tail in lines. Caimans that left pools in response to disturbance buried in mud near pools or in leaf litter in forest.

Resumen

Movimento terrestre coordenado não tem sido registrado em crocodilianos. No entanto, entre 1989 e 1999, 94% de 525 Caiman crocodilus yacare encontrados em terra no Panatanal estavam em grupos coordenados (n = 73) andando um atrás do outro, em linhas quase retas. Os jacarés saíram das poças e iniciaram movimentos terrestres espontaneamente, e em resposta às perturbações por pesquisadores e caçadores. A razão sexual dos grupos foi tendenciosa para machos (0,8 ± 0,24), e foi semelhante daquela encontrada em ambientes aquáticos na área de estudo. No entanto, dois grupos consistiram apenas de fêmeas. Quando os jacarés saíram de poças sujeitas a perturbações, como caça clandestina e captura para pesquisa, eles andaram em linhas um atrás do outro e depois se enterraram na lama perto das poças ou em serrapilheira na floresta.

Fig. 1.

Distribution of sizes of caimans captured moving (A) solitarily (n = 34 individuals) and (B) in groups (n = 491 individuals) in the Pantanal, Brazil, between 1989 and 1999

Fig. 2.

Caimans (circled) in a group undergoing terrestrial movement across a paddock in the Pantanal

Fig. 3.

Frequency of encounter of groups at different times of day. (A) Groups in spontaneous movement, (B) groups induced to leave the pools by human disturbance

Received: 22 Sept 2002

Accepted: 14 Mar 2003