Date of Graduation
Davis College of Agriculture, Natural Resources and Design
Animal and Nutritional Sciences
James T Anderson
American Crocodiles (Crocodylus acutus) are large-bodied crocodylians broadly distributed throughout coastal and lowland wetlands in the Americas. Despite their being large, charismatic megafauna, the study of American Crocodile ecology is still lacking in many areas. As such we assessed the behavior and bioacoustics of American Crocodiles in Belize to address the paucity of data regarding these two facets of American Crocodile ecology. We conducted behavioral observations from three sites in the coastal zone of Belize. We categorized American Crocodile behavior and recorded activity duration for observed behaviors. In conjunction with behavioral data, we also assessed study sites to quantify the intensity of anthropogenic impact. Our results determined that American Crocodiles spent the highest proportional time performing maintenance activities to fulfill basic biological needs. However, the proportion of social and agonistic activities differed between sites, and was greater at sites with higher human disturbance. The results from this project establish activity-budgets for American Crocodiles in Belize as well as indicate adverse behavioral responses to anthropogenic impact which should be further considered in management decision making, as should bioacoustics.;American Crocodiles, like most crocodylian species, have a repertoire of acoustic signals used to communicate intraspecifically and in interaction with their environment. Of the acoustic calls produced, distress calls play an important role in crocodile ecology, particularly for juvenile American Crocodiles. The distress call is produced to elicit a defense response from nearby conspecifics, enhancing the survivorship of young American Crocodiles. We recorded American Crocodile distress calls from three sites in the coastal zone of Belize. We recorded from captured hatchling, juvenile, sub-adult, and adult American Crocodiles. We measured temporal and spectral parameters of the calls to describe the call structure of this species for each size class. We compared call parameters among size classes and determined that call structure remained similar among size classes but call parameters differed. We found that hatchling and juvenile distress calls were highly modulated and higher in frequency, whereas sub-adult and adult calls were longer in duration, lower in frequency, and had less modulation. We determined that call parameters could be used to successfully classify 82.4% of individuals into the correct size class. We also recorded call production by captured individuals as not every capture resulted in successful acoustic recording. Proportion of calls produced by individuals differed by size class and site. We found that American Crocodiles at sites with high anthropogenic impact produced distress calls at a higher proportion. Our results indicate that anthropogenic activity in crocodile habitat may be impacting the acoustic ecology of American Crocodiles in Belize.;The study of crocodylians, in this case American Crocodiles, benefits from the ability to effectively discern individuals in the field. Conventional identification techniques are to physically alter captured crocodiles by clipping the upright caudal scutes. However, this technique is difficult to observe accurately in the field and has no passive marking alternative. In compliment to the behavioral and acoustical study of American Crocodiles in Belize, we implemented novel marking techniques through tail spot pattern coding and visual tagging. We used existing tail spot pattern coding methodology developed for Nile Crocodiles (Crocodylus niloticus), and adapted this technique to create a second method. The original coding protocol, numeric code, was 84% successful in differentiating tail spot patterns from American Crocodiles and sympatric Morelet's Crocodiles (Crocodylus moreletii ). The second method, the additive code, integrated irregular scale groups and vertical caudal scutes into the original coding system. We were 99% successful in differentiating individual crocodiles using the additive code. In conjunction with tail spot coding, we applied flexible, self-piercing, plastic tags to tail scutes to mark sub-adult and adult American Crocodiles. We used the tail tags to verify spot pattern recapture and facilitate individual identification for behavioral observation. The use of these tags is beneficial to behavioral studies and short-term population monitoring and offer an opportunity to augment current marking techniques. We determined that spot pattern coding and visual tagging are effective means to individually identify crocodiles in Belize and are a tool that can be easily implemented by current managers as well as integrated into community based citizen science initiatives.
Boucher, Miriam, "Bioacoustics and Behavior of American Crocodiles in Belize" (2017). Graduate Theses, Dissertations, and Problem Reports. 5239.