Example of unknown echolocation clicks likely produced by beaked whales.

<p><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0036128#pone-0036128-g007" target="_blank">Figure 7a</a> shows a spectrogram of the ‘double click’. Recording was made at 500 m depth. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0036128#pone-0036128-g007" target="_blank">Figure 7b</a> represents a spectrum of the click (solid line) and the background noise level at the time of the recording (dotted line). Spectrogram parameters used to generate plots: frame size 32 samples (0.16 ms), FFT size 128 samples (0.64 ms), overlap 94% (0.15 ms), and Hamming window, for a spectrum filter bandwidth of 24.6 kHz. Data were high-pass filtered at 10 kHz prior to processing.</p

Locations of acoustic encounters as derived from the manual data analysis.

<p>Panels indicate locations of [a] beaked whale, [b] delphinid, and [c] sperm whale acoustic encounters. Size of each dot represents the percentage (logarithmic scale) of acoustic data recorded per glider dive containing respective target signal. Map source: Google Earth. Contours: Hawai'i Mapping Research Group, School of Ocean and Earth Sciences and Technology, University of Hawai'i, USA.</p

Glider track (colored line) and surfacing positions of tagged Cuvier's beaked whale (black dots) on 3 November 2009.

<p>Glider depth is color-coded. Black stars indicate position of glider at times of beaked whale surfacing events. Red star indicates position of glider when Cuvier's beaked whale clicks were acoustically detected by the glider during the mission (detections were verified in the post deployment analysis). The acoustic system was operated at depth between 500 m and 1000 m indicated by greenish/bluish colors. Times are UTC.</p

Map of the study area off the Kona coast, Hawai'i, USA.

<p>Inset at upper right shows the Seaglider at the beginning of a dive. Bathymetric map source: Hawai'i Mapping Research Group, School of Ocean and Earth Sciences and Technology, University of Hawai'i, USA.</p

Glider track (v-shaped line) and hypothetical dive profile of tagged Cuvier's beaked whale (u-shaped line); see text for details.

<p><b>Blue line indicates the time/depth when the acoustic system of the glider operated.</b> Red line represents time/depth when Cuvier's beaked whales were acoustically detected by the glider. Green line marks periods when the whale was presumably vocally active. Black star indicates surfacing position of the whale. Remarks: [1] This graph does not consider horizontal distances and the orientation of the whale towards the glider. [2] For illustration purposes, the whale's dive profile was limited to deep dives only.</p

Principal acoustic features of echolocation clicks of regular click trains produced by Blainville's (<i>Mesoplodon densirostris</i>) and Cuvier's (<i>Ziphius cavirostris</i>) beaked whales.

<p>Values are based on Johnson <i>et al.</i>, 2004.</p

Percentage of manually analyzed acoustic data containing sperm whale vocalizations for respective glider dives.

<p>Percentage of manually analyzed acoustic data containing sperm whale vocalizations for respective glider dives.</p

Percentage of data containing target signals in the respective hour of day as derived from manual data analysis.

<p>The mean observation duration per hour of day was 484±129 minutes (range 250–696 min). Shaded areas indicate hours before/after sunset. Note different scales of y-axes.</p