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Newsletters may offer personalized content or advertisements. Learn more. Follow us. Fristrup and Harbison 17 suggested that sperm whales forage actively using vision to identify and locate prey. This visual predation hypothesis predicts that sperm whales may detect their prey by its bioluminescence or should consistently turn their ventral side towards the surface to facilitate stereo vision of silhouetted prey 6. In , Norris and Harvey 18 proposed that sperm whales use echolocation to find and discriminate prey by producing powerful biosonar clicks with their hypertrophied nasal complex.
These source properties and the fact that sperm whales produce clicks throughout their foraging dives strongly suggest that sperm whales use long-range echolocation to find prey 7 , 24 , 25 , 26 , Gordon 24 also proposed that echolocation is used during the last seconds of prey acquisition and compared the fast bursts of clicks also called creaks recorded from diving sperm whales with buzzes produced by bats in the terminal phase of prey capture Miller et al.
This coupling between buzzing and movements lends support to the hypothesis that sperm whale buzzes play a role in active prey acquisition as is the case for beaked whales 30 , porpoises 31 and delphinids Furthermore, it was shown that buzzes occurred both while moving up and down in the water column 29 , suggesting that visual imaging of prey against down-welling light is not essential for sperm whale hunting as also evidenced by the findings of healthy, but blind sperm whales 6.
However, while echolocation can explain how sperm whales find and track their prey, it does not address how the largest toothed whale is able to catch highly mobile nektonic prey which make up a portion of its diet. This hypothesis presents a coherent scenario potentially explaining both the apparent hunting success of these large predators 7 and the evolutionary driving force behind the hypertrophied nasal complex. A prerequisite for acoustic debilitation is that the prey is negatively affected by sound pressure levels within the capabilities of the sperm whale sound generator.
However, transients from both a spark generator and blasting caps have significant energy at low frequencies coupled with very fast rise times and therefore little spectral and temporal resemblance to toothed whale echolocation clicks. A detailed understanding of how sperm whales catch prey and a specific test of the different and in some cases opposing hypotheses require fine scale data on the acoustic behaviour of foraging sperm whales and simultaneous information about the spatial relationship with their prey.
Here we use high resolution sound and movement recording tags on free-ranging sperm whales to quantify their behaviour during prey captures. Our analysis supports previous reports that sperm whales forage actively and confirms that sperm whales do not consistently orient themselves as predicted to optimise the use of visual cues provided by the downwelling light. We also show that sperm whales do not debilitate prey acoustically, but rather employ a fast repetition rate buzz to provide high resolution echolocation sampling during active prey chases. We propose that prey are subdued near the end of the buzz with a rapid acceleration consistent with fast movements of the mandibles and the tongue to grasp and suck in prey.
Buzzes were produced mostly during the bottom phase of foraging dives Fig. In total the whales produced buzzes that lasted a median of 9. Of these, buzzes matched the criteria used here to select independent buzzes see Methods and thus were included for further analysis Table 1. A Image of sperm whale b tagged in off northern Norway.
The figure shows the tag position at the moment of deployment. B Section of a dive profile recorded from a male sperm whale off northern Norway. The colour indicates approximate swim speed estimated using a Kalman filter matching pitch angle to depth rate. This estimate loses accuracy at low pitch angles. Each grey circle marks a prey capture attempt buzz. C Roll orientation of the diving sperm whale during the foraging dive. Coloured bars denote different animals. As exemplified in Fig. By design, the Kalman filter used to estimate speed in this figure tends to de-emphasize short bursts of high speeds associated with prey chases.
Also, swimming speed is poorly estimated at low pitch angles. This analysis shows that the whales moved forward during prey capture attempts at an average speed of 1. Fristrup and Harbinson 17 proposed that vision is essential for sperm whale foraging and hypothesized that whales should roll upside down to facilitate stereo vision 6 of prey against down-welling light.
To test this we computed the absolute roll angle of sperm whales throughout the foraging phase of dives, that is, between the first and last buzz within each dive 7. The histograms of roll angles showed a bimodal distribution, with peaks around 10 and degrees, for both dive types Fig. The acceleration rate jerk was computed in the nominal approach phase and during the buzz to test for transients consistent with prey capture Jerk was normalized to the mean jerk during steady swimming see Methods , and a normalized jerk threshold of 5, derived by the log-frequency distribution of the normalized jerk in approach and buzz phases, was used to detect strong transients.
Peaks in normalized jerk during buzzes had a mean of 73 interquartile range, 12 to 72 , some 20 times higher than the normalized jerk during steady swimming Table 1. For these 27 buzzes, the prey range at the start of each buzz was estimated by back-calculation, using the time delay between the normalized jerk peak to the start of the buzz to estimate the hand-off distance, i. Jerk was normalized to steady swimming. Values during steady swimming are represented in white.
Values above the threshold set at 5, as indicated by the red line in C , represent abnormally fast movements. C Individual-weighted average of normalized jerk black line for buzzes shown in B. The upper and lower limits of the grey coloured area represent the maximum and minimum values of the individual averages, respectively. The red line denotes the 5 threshold used to detect a jerk transient. D Inter-click interval and normalized jerk signature of an echolocating sperm whale during a prey pursuit.
Clicking alternates between faster and slower rates, accompanied by high jerk transients. The sperm whale may be tracking acoustically the moving prey by increasing its ICIs when prey escapes, and occasionally attempts to capture prey as indicated by the high normalized jerk when close enough. Using the normalized jerk peaks as an indicator of when prey are intercepted during a buzz, we quantified the ICI and the apparent output level AOL as a function of time, and therefore range, prior to target interception Fig.
Although ICI and AOL changed continuously through the approach and buzz, there was a major transition at the switchover from usual to buzz clicking. This was marked by an order of magnitude reduction in ICI from about 0. The impact of this on the potential acoustic field of view 39 can be visualized by comparing the ICI with the estimated two-way travel time TWT from whale to prey Fig. While the 0. A Sperm whale shallow foraging dive profile with four prey capture attempts, i.
The black line indicates the echolocation phase of the dive. B—D represent different parameters from the start of the buzz to the peak in normalized jerk, taken as a proxy for prey interception. B A detailed view of the click rate during the final buzz encircled in black in A. The red line marks the estimated two-way-travel time TWT from the sound source to the presumed prey capture location calculated from the forward speed of the whale. Note the log scale on the TWT axis.
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C Normalized jerk signature during the same period and D distance between the front of the whale and the presumed prey interception location, derived from the forward swimming speed of the whale, calculated using the orientation-corrected depth rate method. During the usual click approach phase the tagged whales showed a bimodal pattern in ICI: the low-latitude whales produced stable ICIs up until the start of the buzz Fig. During buzzing all tagged whales continuously decreased ICI Fig.
As most usual clicks were clipped in the recording, an accurate measure of the AOL reduction from usual clicking to buzzing is not possible but a reduction of 1—2 orders of magnitude in peak pressure is conservative i. The histograms on the right show the ICI distribution in the approach phase.
Each colour represents a different animal. When sperm whales switch to a buzz they increase click rates and lower source levels by some 2 orders of magnitude This ensonification provides a unique example of the sound field that may be received by a prey as it is approached by an echolocating sperm whale at depth Fig.
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The received buzz clicks, which were not clipped due to the lower SL during buzzes, showed the distinctive monopulse nature of sperm whale on-axis clicks Fig. A Absolute sound pressure level recorded by the tag. C The waveform and D power spectral density SPD of the 5 most powerful clicks received on the tag grey lines and the mean overlaid black line. In the last decades, the development of new tools to study the sounds and movements of free-ranging echolocating whales has extended our knowledge about sound production in sperm whales 21 , 22 , 40 , 41 , the acoustic properties of their clicks 23 , 42 , 43 , their echolocation behaviour 44 , 45 , 46 , 47 , 48 and movements during foraging 14 , 15 , 16 , 29 , However, information about how the largest tooth-bearing predator in the world tracks and captures small and agile prey is still scarce.
A number of hypotheses have been advanced, but they remain largely untested due to the difficulties in sampling fine-scale predator-prey interactions in the deep sea. To address this data gap we used multi-sensor tags to obtain a high-resolution picture of the movement and acoustic behaviour of free-ranging sperm whales during prey capture. This unique data set allows us to address the three hypotheses for how sperm whales hunt and capture their prey: the visual predation hypothesis 17 , the biological big bang hypothesis 12 and the hypothesis of suction feeding To do so, we rely on a well-established indication of when whales are attempting to capture prey in the form of echolocation buzzes.
Strong evidence for the role of buzzes in close prey approaches has been found in beaked whales where echoes from prey can be monitored 30 and the consistent connection between buzzes and movement in sperm whales 29 , beaked whales 51 , porpoises 31 and dolphins 32 suggest that they serve the same role in other echolocating species. Using the end of the buzz as a first proxy for when whales have completed or abandoned the capture, we examine how tagged whales move in the preceding seconds.
In the following we will use these new data to critically evaluate the three hypotheses for how sperm whales hunt and capture their prey. Animals will likely make use of all sensory cues available to improve the efficiency of their activities Fristrup and Harbinson 17 proposed that vision is central to sperm whale foraging and predicted a ventral-upward posture of sperm whales in order for them to use stereo-vision to search for silhouetted prey against a bright background. Such visual predation should be more prominent in well-lit shallower waters Our data show that tagged whales did not consistently swim upside down to spot and track prey silhouetted against the lit surface waters using stereo vision Fig.
Instead, they spent a large portion of their foraging time rolled to one side which would enable only monocular vision of prey in down-welling light.
https://hochmortsolbio.tk Although sperm whales may be complementing echolocation with monocular vision, the fact that the whales use similar rolling behaviour in shallow and deep dives despite the very large difference in light levels, suggests that this behaviour has little to do with vision.
Rather this finding may indicate that sperm whales have preferred approach angles for echo-guided prey capture.