The following copyrighted material cannot be copied for profit. You may however, use it for non-profit scholarly purposes. Citation for this article is: 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 Tiputini River (Amazonian Ecuador) during March 2000.

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 neonateís 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 Tiputini River. However, we regularly saw juvenile (< 20 cm SVL) spectacled caiman (Caiman crocodilus) and larger dwarf caiman ( 40 cm SVL) using the main river. Neonate dwarf caiman may rear in small forest streams with dense forest vegetation because they gain greater protection from predators in such habtiat. If true, deforestation of small forest streams, like this one, may seriously impact the survival of neonate dwarf caiman.

Data for this contribution were collected during a course of tropical ecology by Boston University and Universidad San Francisco de Quito at Tiputini Biodiversity Station. We thank Mayer Rodriguez, Hendry NarvŠez, Franklin NarvŠez, Jaime Guerra and Bradley Kline for their help in the field work and Kelly Swing for comments on early versions of the manuscript.

Submitted by JENNIFER M. WHITE. 30 Sugar Hill Rd, Killingworth CT, 06419 and Jesķs A. Rivas. Dept. Ecology and Evolutionary Biology, University of Tennessee, Knoxville, TN 37996; e-mail: anaconda@prodigy.net.