Table 1.

Parameters analysed during navigational trials in three tasks for two harbour porpoises

Task/porpoise
atb bta atb+
ParameterFrejaEigilFrejaEigilFrejaEigil
Mean navigational time per trial (s)9.1±1.79.0±0.78.4±1.18.9±1.16.9±1.66.7±1.6
Mean navigational distance per trial (m)27.1±3.126.4±1.525.1±3.427.1±1.7--
Mean no. of clicks recorded per trial163.8±76.4191.0±47.2185.3±50.0208.5±17.495.8±19.288.0±18.9
Mean speed (m s-1)4.0±0.13.8±0.14.0±0.13.8±0.2--
Mean lag time (ms)19.2±1.217.6±1.114.4±0.616.8±0.535.7±2.926.4±1.7
Slope (±95% confidence interval) (ms m-1)0.91±0.231.32±0.291.12±0.181.21±0.131.03±0.661.86±0.36
• A navigational trial is the distance travelled during the time frame where echolocation clicks could be analysed (see Materials and methods). The table gives mean time and mean distance values (± s.d.) of the duration of click trains and the number of recorded clicks, as well as mean speed, mean lag time (± standard error) and the slope of regression (±95% confidence interval) of the median click interval over distance to reference point.

Number of trials included for Freja/Eigil are: atb=9/8, bta=8/8 and atb+=5/5. In atb+, the navigational trials were shorter than in atb and bta (see Materials and methods). This causes a shorter navigational time as well as a lower number of recorded clicks for atb+ compared with the other tasks. For atb+, no navigational distance and no speed could be determined, as no recordings were taken with cam2 (see text).