Marine Mammal Cognition
Visual discrimination in Manatees
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More information concerning Monika Lechermeier
Introduction
All species of sireneans are considered to be either endangered or threatened. Without adequate and up-to-date scientific data, however, regarding manatees and their habitat, efforts to manage and conserve them will not be as effective as they could be. A lot of recent research has concentrated on population dynamics. Questions on navigation and orientation have been unexplored and little is known about the sensory apparatus and capabilities of sireneans even though such knowledge is important to an understanding of their behavior and ultimately their survival. Collision with motorboats is a number one cause of mortality in manatees. So in trying to learn how manatees can avoid water vessels sensory studies are becoming an increasingly important area of investigation.
Study
The aim of this study is to gain more insight into the visual system of manatees. The question for the role of the visual channel in the manatees' life is raised as well as for the role of vision in air. The results should allow to answer questions on the efficiency of visual signals in alarming manatees to prevent injuries and death associated with water vessels or fishing gear and might lead to ideas for designing such signals. At the moment this study is concentrating on the estimation of visual acuity in air.
Procedure
The manatees' visual abilities are investigated in a behavioural study. A standard test pattern is used for measuring visual acuity with grid lines varying in width (Ronchi rulings). This stimuli configuration allows to measure visual acuity uncontaminated by intensity discriminations. In a twofold simultaneous discrimination task the subject is asked to choose the finest grating- the standart target (not allowing resolution and therefore appearing as a flat grey target) over a variable target. After approximation of the visual threshold the thresold is obtained by the psychophysical method of constant stimuli. After a warm-up period with a suprathreshold target each of the approximated variable gratings is paired with the standard grating in a strategy tested pseudorandom series.
Training
Standard conditioning methods were used for training the animals. Since there is no possibility to separate the subject animal during trials by a gate, training also involved separation of the other animals via target tracking and stationing at individual stationing targets. This turned out to be very time consuming but the training can be seen as behavioural enrichment for the animals and apart from collecting data for the actual research it allows other interesting behavioural observations on manatees in captivity.
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