Individual distinctiveness, short- and long-term comparisons, and context specific rates of Florida manatee vocalizations

UNCW Author/Contributor (non-UNCW co-authors, if there are any, appear on document)
Lynne Elizabeth Williams (Creator)
Institution
The University of North Carolina Wilmington (UNCW )
Web Site: http://library.uncw.edu/
Advisor
Laela Sayigh

Abstract: In the 1980?s, Thomas J. O?Shea recorded captive and wild Florida manatees (Trichechus manatus latirostris), and statistical analyses of various acoustic features of their calls indicated possible individual distinctiveness. To further test the hypothesis that manatee calls contain individually distinctive features and to test the hypotheses that various acoustic features of their calls are stable over short (1-3 year) and long (19+ year) time periods and that vocal rates vary depending on behavior, recordings of wild and captive manatees were made between November 2002 and January 2004. Recordings of 31 manatees (21 wild, 10 captive) were obtained and vocalizations from two additional manatees recorded only in the 1980?s were analyzed, for a total of 33 individuals. Four of these manatees had been recorded both in the 1980?s and in 2002-2004, and the vocalizations of these individuals were used for long-term comparisons. Cross-validated linear discriminant analyses using nine different parameters of manatee vocalizations determined that 1) when using only the most recent recordings, vocalizations were classified to the correct individual a greater percentage of time than expected by chance for 30 out of 33 animals; 2) an overall higher percentage of calls was correctly assigned to only one of four animals recorded in the 1980?s when using all recordings versus just the most recent recordings; 3) when using only adult and calf vocalizations, calls were assigned correctly to both adults (82.2% of 506 vocalizations) and calves (79.5% of 503 vocalizations) a greater percentage of time than expected by chance; and 4) when using only calf vocalizations, calls were assigned correctly to both females (66.0% of 250 vocalizations) and males (58.1% of 253 vocalizations) a greater percentage of time than expected by chance. ANOVAs were performed on each of the nine parameters for individual manatees that were recorded: 1) over 19+ years, 2) when less than one year old and again between the ages of one and three, and 3) as adults in at least two separate field seasons. For three individuals recorded over 19 years, 47% of tested parameters did not significantly change over that time period; all three individuals were calves in the 1980?s. For the one individual recorded over 22 years, 33.3% of his parameters did not significantly change over that time period. For four individuals recorded when they were less than one year old and then again between the ages of one and three, 71% of tested parameters did not significantly change. For four individuals recorded as adults in at least two separate field seasons, 76% of tested parameters did not significantly change. These results indicate that manatee vocalizations are individually distinctive, and that there are age and sex differences in calls. These results also suggest that 1) many call parameters are apparently not stable from calf to adulthood in at least some individuals, 2) some calves, subadults, and adults show variable changes in parameters over short (1-3 year) time periods, and 3) some calves and adults show stability in all parameters over short time periods. Florida manatee vocalization rates were not affected by group size at Blue Spring State Park, Florida, although they were found to differ depending on behavior. When looking at call rates per minute averaged across group sizes, significantly higher vocalization rates occurred during social activity than during bottom resting, with boat, and play; mill had significantly higher rates than bottom rest and with boat; and surface rest had significantly higher rates than bottom rest. Overall, the hypothesis that Florida manatee vocalizations are stable over long time periods was not supported, although only one adult was tested. Conflicting evidence for short-term stability in both calf and adult calls was found, with the number and type of parameters that changed being highly variable. Results supported the hypotheses that Florida manatees have individually distinctive vocalizations and that vocal rates vary depending on behavior. These results add to a growing body of information on manatee behavior and communication, and could potentially contribute to manatee research and conservation efforts by providing a means to document the presence of specific individuals, the presence of manatees from different age classes and sexes, or the occurrence of certain behaviors without having to conduct boat-based surveys.

Additional Information

Publication
Thesis
A Thesis Submitted to the University of North Carolina Wilmington in Partial Fulfillment Of the Requirements for the Degree of Master of Science
Language: English
Date: 2009
Keywords
Manatees--Behavior, Manatees--Florida--Blue Spring State Park, Manatees--Vocalization
Subjects
Manatees -- Florida -- Blue Spring State Park
Manatees -- Vocalization
Manatees -- Behavior