Proyecto Terciopelo
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Projects:
Very brief descriptions of the various components of my work:
1. Spatial Ecology of Bothrops asper
| Radio-tracking | Implanting a transmitter |
From November 2004-December 2006, I used radiotelemetry to study movement patterns and habitat usage of fer-de-lance at La Selva. Small radiotransmitters were surgically implanted into the body of a snake, which allowed us to locate the snakes using a handheld receiver and antenna. We located animals on a daily basis, alternating daytime and nighttime observations to determine their daily activity patterns. At each snake location, we recorded its coordinates within La Selva, as well as its behavior, general habitat, and a series of microhabitat variables. With ArcView GIS software, we use this data to map the animals’ position over time, determining their movement rates, habitat usage, and home range size. A second protocol of 24-hour monitoring of a single individual was used to determine daily activity patterns.
| Gravid female resting on the buttress of a tree |
2. Ecosystem Role of Bothrops asper
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| Rodent choice experiment | Seed-predation experiment |
Because fer-de-lance are abundant and widespread predators, they may be an important component of many Central American ecosystems. We are investigating the hypothesis that B. asperinfluences the behavior of seed-feeding rodents, thus indirectly mediating seed-predation rates. To test this, we conducted behavioral experiments both in laboratory settings and in the field to determine how rodents respond to the presence of snake predators. Specifically, we are testing whether A) rodents avoid areas where snakes are or have been present, and B) whether rodents alter their foraging strategies when snakes are present (long story short: they don't do either one). Both experiments were repeated in the laboratory, under semi-natural conditions, and in the field.
We have so far found rodents to be exceptionally
difficult to capture at
La Selva, presumably due to extremely low population densities. Thus we use a second,
higher-altitude field
site located in Jicotea de Turrialba for all snake-rodent experiments.
3. Diet
 A common technique to study snakes’ diet without killing them is to manually force an animal to regurgitate its prey. However, this can be very stressful to the animal (and in the case of large venomous snakes, very stressful to me). We did not wish to influence the behavior of snakes that are being radio-tracked, so those individuals were excluded from dietary studies. We instead relied on capturing as many additional animals as possible, from which we recorded morphological data, marked them with a small PIT tag for future identification, and released them once we obtained a fecal sample.
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4. Supplemental Feeding
Resource limitation is one of the primary factors in determining the life-history characteristics of an organism. Our own trapping efforts, as well as those of several other researchers, found that rodents are quite rare at La Selva, although such was not always the case (i.e., see Fleming 1974, Ecology 55: 493-510). Data from our first year of telemetry indicated that fer-de-lance at La Selva rely heavily on frogs as prey, and several radio-tagged snakes ostensibly starved to death during the year. These factors all suggest that this B. asper population is strongly limited by prey availability.
To test this, we initiated a second year of radiotelemetric tracking in December 2005, along with a supplemental-feeding program. One group of tagged animals was fed prekilled rats in the field, while control animals were left to forage naturally. Preliminary analyses suggest that supplementally-fed snakes gain more body mass, have smaller home ranges, move shorter distances and with less frequency, spend less time foraging, and utilize less swamp habitat. Neat!
Though I conducted many feeding sessions, it proved extremely difficult to capture on film (it was really cool though). In the meantime, an artist's interpretation of the technique:
