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White, J. M. and J. A. Rivas, 2003. Paleosuchus trigonatus (Dwarf Caiman)
Neonate time budget. Herpetological Review. 34 (2): 141 Click here for a pdf
PALEOSUCHUS TRIGONATUS (Dwarf Caiman) NEONATES TIME BUDGET.
Natural history of forest-dwelling animals is often poorly understood because
of the difficulties in observing them. Further, studying neonates can be
especially difficult as their small size and cryptic nature limits field
observation (Morafka et al. 2000. Herpetol. Monogr. 14:353-370). Dwarf caimans
are no exception to this pattern, and few studies have dealt with their natural
history (Magnusson et al. 1991. J. Herpetol. 25:41-48; Rivas et al.
2001. Herpetol. Rev. 32:251), and none have addressed neonate behavior.
Here, we present preliminary observations on the behavior of neonate dwarf
caimans in a creek in the
On 30 September 1999, we discovered a dwarf caiman nest in a low height, seasonally-flooded varzea forest 4.5 m from the at the base of a tree from a small creek. Based on finding eggshells characteristic of recent hatching at least 12 neonate dwarf caiman are thought to have emerged from this nest on 27 November 1999 (Rivas et al., op. cit.). Five neonate dwarf caiman (mean total length = 30.6 cm, range: 29.9-32.8; mean mass = 103 g, range: 85-120 g) found 19 March 2000 in a small stream (mean width = 1.6 m, mean depth = 0.2 m) < 50 m away are believed to have originated from this nest. To study the time budget and behavior of these neonates, we conducted night observations from 1900 to 0600 the next day. During night observation periods, we recorded the behavior of as many neonates as we could find. We found 4, 2, and 1 neonate dwarf caiman, respectively, on 22, 29 and 30 March 2000. As we did not handle the animals prior to observations, we were unable to determine whether we saw the same animals on different nights; we pooled all data across nights for analysis. We recorded data every 10 min on each animal (using their eyeshine) by turning on a dim flashlight for a brief (5-10 sec) interval. The neonate’s head position relative to the water surface (as low [eyes barely showing], intermediate [upper but not lower jaw above waterline] or high [lower jaw at least partly out of water]) and its distance from shore/water edge (cm) was recorded at each interval. We also estimated height over the water (in m) of the lowest plant that directly overhung each caiman, potentially concealing it from possible predators. If an animal was present at the beginning of the night and disappeared from one observation interval to the next, we assumed that it was hiding or under the water as we were monitoring a long (ca. 30 m) stretch of creek and the neonates were unlikely to have moved out of the area.
We made 410 observations of neonate dwarf caiman. Neonate caimans spent most of their time (91%; N = 266) within 0.5 m of shore; relatively little time was spent mid-stream far from the bank. Neonates were also found beneath relatively low overhanging vegetation (i.e., within 1 m of the water surface) 62% (N = 190) of the time, which may indicate selection for relatively sheltered areas. Neonate dwarf caiman were immobile in 51 % (N = 206), out of sight (probably immobile as well) in 27% (N = 112), and active in only 22 % (N = 91) of the observations. Caimans changed locations between observations more often before 2300 and were more frequently concealed after 0200. Most of the time (83%; N = 246), neonate caimans held their heads high. Holding the head elevated has been associated with territorial behavior in caimans (Verdade 1999. Herpetol. Rev. 30:38-39). Lack of aggregation among neonates, a feature of clutch pods among many crocodilians; lack of distress calls during our periods of observation; and absence of adult dwarf caiman reported previously for this creek (Rivas et al., op. cit.) collectively suggests that the neonates we observed may already be on their own, implying that parental protection in this species, if it exists, is short-lived.
During the 2 months that we spent surveying caimans in the area, we did not
detect any other dwarf caiman of a size similar to these neonates in the
Data for this contribution were collected during a course of tropical
ecology by
Submitted by JENNIFER M. WHITE.