Water Craft Avoidance Sound Studies:
Florida manatees, an endangered species, are killed every year as a result of boat accidents. Since 1974, more than 4000 dead manatees have been collected in Florida, and about 30% of these deaths have been attributed to collisions with boats or fatal injuries by propellers. Manatees sometimes feed close to the surface of the water, and for reasons that are n
ot fully understood, do not seem to be able to hear the sound of approaching boats. It has been suggested that at the surface of the water, sound transmission is blocked through surface reflection and also by boat shadows. One of the major purposes of our on-going research has always been to understand the meaning behind vocalizations produced by manatees in captivity and in the wild. Our earliest studies, which are still ongoing since 2001, were directed towards producing natural or artificial sounds that would cause manatees to avoid on-coming water craft. We have so far been unsuccessful in identifying simple artificial single or double frequencies that we can project into the water that will effectively and/or reproducibly cause behavioral avoidance in our manatee subjects. However, before we can identify such sound patterns we have to learn more about manatee communications. Passive Manatee Vocalization Recordings and Associated Behaviors and Vocalization Classification:
To expand our research vocalization database, we will continue to record manatee vocalizations from animals housed in a captive setting at the Cincinnati and Columbus Zoos in Cincinnati, Ohio, as well as the Parker Aquarium and Homosassa Springs in Florida. Also, we usually videotape the manatees at the Cincinnati and Columbus zoos when they are vocalizing to study manatee behaviors that may be associated with different vocalizations. Some of these studies are beginning to pay off, primarily because of the hard work of our senior research students. They have viewed many hours of video recordings while listening to the animals vocalizing and then noted any behaviors that occurred when a manatee squeaked. In addition, the large number of vocalizations recorded in our research database library in the lab has allowed us to categorize specific components of manatee vocalizations and develop a classification method that may prove to be of use in future studies. In the future, we hope that we may use this work for vocal identification of manatees in field settings where visibility is poor. If we can reproduce and accurately identify individual manatees by their specific vocalization characteristics, then we can use this information for vocal identification of animals that have been released and are being tracked in the wild. Off Site Vocalization Recordings:
In the last two years we have installed underwater hydrophones at various locations that house captive manatees. Currently, we have hydrophones located and operating at the Cincinnati and Columbus Zoos, and in Florida at Homosassa Springs Animal Park and the Parker Aquarium at the South Florida Museum. Underwater sounds, including manatee vocalizations, are received by these hydrophones, fed to on site equipment, and then transmitted through the internet to our laboratory at Xavier University. These sounds are then decoded, processed, and recorded on a special computer for later review. At present, our students are involved in monitoring these recordings and counting vocalization events. However, due to the large size of our data sets, we are currently working on computer software that will automate our review of these massive data files. We expect this software to be up and running by March of 2011. This software will allow us to identify various patterns present in manatee vocalizations, which will hopefully provide some understanding of their communication, and allow us to create a library of manatee squeaks with associated behaviors. We plan to utilize our massive database of vocalizations from these off-site locations to study such diverse factors as circadian and circannual rhythms in manatees, differences in vocalization patterns between males and females, and between females with babies, possible effects in vocalizations due to animal age, wild vs captive animals, and effects due to ambient temperatures, tidal movements, etc. Many of these factors may not alter patterns of vocalizations, but until they are studied, we will not know which may or may not be significant. So stay tuned for later updates. This research is supported by Xavier University in Cincinnati Ohio. The research has been approved and licensed by the U.S. Fish and Wildlife Service. The research projects have also been approved by the Cincinnati and Columbus Zoos who house manatees from Florida who are being rehabilitated before they are released back into the wild, and also by the Parker Aquarium and Homosassa Springs. Charles J. Grossman, PhD and Professor
Department of Biology, Xavier University, Cincinnati OH
and the Director of the Midwest Florida Manatee Research Project
