2012 COURSE DATES: AUGUST 4 – 17, 2012 - Sirenian International

Fish Sci (2011) 77:795–798 797
was included as a random factor. The most parsimonious
model was selected based on the Akaike information criterion
(AIC). For all statistical analyses, we used the
software R, and the GLMM was analyzed using the
package lme4 and the function lmer.
Results
The GLMM for illumination intensity including the day–
night difference as an explanatory variable was the best
model, with the lowest AIC. The model had an AIC value
that was 578.2 lower than the second best model, which
included random effects only. This suggests that illumination
intensity clearly differed between day and night
(GLMM: day–night, estimated value during the day:
1161.0 ± 63.5 SE, night: 1.1 ± 63.5 SE).
The GLMM for the number of events of avoiding
behavior that included the day–night difference as an
explanatory variable was the best model, with the lowest
AIC (Table 2). This model had an AIC value that was 31.1
lower than the second best model, which included random
effects only. These results suggest that the number of
events of avoiding behavior differed between the day and
night: these subjects showed a greater number of events of
obstacle avoidance behavior during the day than at night
(GLMM: day–night, estimated value during the day:
1.7 ± 3.5 SE, at night: 0.8 ± 1.1 SE).
The model with the lowest AIC value with respect to
the number of events of bumping or active touching
included random effects only (Table 2). The model had an
AIC value of 0.8 and 1.7 lower than the second best
model, which included the day–night difference. The
GLMM for the number of events of bumping (GLMM:
random effects only, 0.9 ± 1.3 SE) and active touching
(GLMM: random effects only, 7.2 ± 2.1 SE) revealed
that it was not related to the day–night difference. The
GLMM for the duration of active touching, including
random effects only, was the best model with the lowest
AIC. The AIC value was 2.0 lower than the second best
model, which included the day–night difference. These
results suggest that the duration of active touching was not
different between day and night (GLMM: random effects
only, 49.8 ± 12.8 SE).
The GLMM for the number or duration of events of
inactive behavior, including random effects only, was the
best model with the lowest AIC. The model had an AIC
value of 0.7 and 0.8 lower than the second best model,
which included day–night. These results indicate that the
number (GLMM: random effects only, 1.3 ± 1.5 SE) and
duration (GLMM: random effects only, 104.4 ± 10.7 SE)
of events of inactive behavior were not related to the day–
night difference.
Discussion
In this study, the number and duration of events of
inactive behavior did not differ between day and night.
Therefore, we concluded that our subjects’ activities did
not differ between day and night, and that it did not affect
their behavioral responses to the obstacle during the
experiments.
Focusing on the differences in behavioral responses to a
net obstacle between day and night, we found that captive
manatees show a greater number of avoidance behaviors
during the day than at night. These results suggest that
manatees can recognize the obstacle more easily during
light periods. However, there was no difference in the
number of bumping events between light and dark periods.
Therefore, accidental bumping may be expected to occur
regardless of the level of illumination and manatee’s higher
degree of associated recognition.
All sirenian species have sparse hairs on their bodies and
orofacial that are of the sinus type, and typically tactile in
function [13–18]. In fact, it has been specifically reported
that a manatee’s orofacial hairs are used for tactile exploration
and discrimination [13–16, 18]. In the current study,
the number and the duration of active touching behavioral
events did not differ between day and night. These results
indicate that manatees heavily rely on their tactile senses to
recognize an obstacle, even during light periods that
facilitate purely visual recognition. In field studies, when
wild Antillean manatees are caught by encircling them with
Table 2 The GLMM models for the number of events of each behavioral response to the obstacle (avoidance, active touching, and bumping of
the obstacle) along with AIC and delta AIC (DAIC) values
Model The number of events of each behavioral response to the obstacle
Avoidance Active touching Bumping
AIC DAIC AIC DAIC AIC DAIC
Random effects only 200.7 31.1 180.8 0.0 48.8 0.0
Day–night 169.6 0.0 182.5 1.7 49.6 0.8
Favoured models (bold type) were evaluated on the basis of the lowest AIC
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