Vocal communication and echolocation in killer whales

Killer Whale Communication

Vocal communication is a vital aspect of the lives of Killer whales. Though several researches have shown their adaptability to interferences, serious disruptions to their aquatic vocal communication system would bear severe negative consequences.

Maintaining our marine ecosystem is not a choice but a crucial responsibility for preserving our own environmental ecosystem. If nothing is done, we can be rest assured that a slow but steady degradation of our own environment is on the cards as a butterfly effect.

Killer whales, known by their biological name as Orcinus orca, are the most common mammal species, next only to humans and are found to inhabit almost all the oceans of the world. They are classified within the dolphin family and their diet is one of the most extensive among the cetaceans comprising a variety of warm-blooded prey. Killer whales are characterized by their large bodies that can weigh between 4 to 6.3 tons in males and 2.6 to 3.8 tons in females. Males are known to grow up to a length of 8 meters and females up to 6.6 meters with a straight and tall dorsal fin that can grow up to 1.8 meters. Killer whales are known to form closely knit groups known as pods. Each pod can have anywhere between 3 to 25 members which live and hunt together. Sometimes several pods can live together forming what is known as superpods that may have more than 150 whales. [Whale Songs] Using a repertoire of sounds called dialect, a pod of whales exhibit effective communication, which is the key to their success as one of the best hunter predators of the ocean. A brief overview of Killer whale communication with the help of some studies is essential for us to understand how vital sound communication is for the killer whales for foraging and hunting. This would also help us understand how this delicate but vital process can be disturbed by humans in the form of acoustic impacts due to increased boat traffic, military sonar, dredging, seismic testing etc.

Killer Whale Communication

Communication is the key to the survival of the killer whales as they depend on effective communication using a variety of sounds such as whistles, clicks, pulsed calls, low frequency pops, jaw claps etc. Killer whales produce sounds by moving air between the nasal sacs. A tissue in the nasal cavity called the dorsal bursa is the site of sound production. They use echolocation clicks to determine the size, shape, distance and even the internal structure of the objects. Killer whale echolocates by producing clicks of high frequency waves called as 'trains', which are focused into a fine beam as they pass through the melon, a rounded region on its forehead, which is made up of lipids. These high frequency clicks are bounced back when they hit an object and the returning waves are conducted through the fat filled lower jaw and passed into the auditory bullia. (the ear) Killer whale whistles range between.5 to 40 KHz. Researchers have observed that the frequency of whistles increases with the proximity of the whales and decreases when the whales are further dispersed. [Seaworld]

Pulsed calls in the range of.5 to 25 KHz are the most common vocalization among killer whales. Researchers have observed that the repertoire of calls known as the dialect is distinct for the different pods and that no two pods share the entire repertoire. It is also observed that pods from very different geographical locations have entirely different dialects. Studies between Norwegian and Icelandic killer whales has revealed that the two groups did not share even one of the 24 different calls that they produced. Calves produce their first pulsed calls around 2 months and continue to develop their vocal repertoire until puberty. [Seaworld] With this basic background let us now review some literature pertaining to the communication system of the killer whales and how sound interference caused by humans cause injury or severe behavioral disruption.

Literature review

Volker et.al (2004) studied the vocal behavior of mammal eating transient killer whales in comparison to the resident killer whales. Observations of these two different ecotypes of Orcinus orca revealed a distinctive adaptive behavior. The research was conducted on killer whale populations in the northeastern pacific waters. Killer whales across the entire sea belt of Johnstone and Queen Charlotte Straits, British Columbia, Glacier Bay, icy strait and southeastern Alaska were studied for this research, which was conducted during the summer months (June to December) during 1999 and 2003. Offshore hydrophones were used to register acoustic activity and laser rangefinders were used to confirm surface activity. GPS location systems were also used to identify swim speed and directions of the whales. Since this research was exclusively focused on communicative pulse calls echolocation signals were not studied. Vocal activity among the two ecotypes for different behavioral contexts were studied and compared. The level of vocal activity during the milling process (after a kill) was specifically recorded to understand if there was any significant difference when compared with other behavioral categories. During the course of the study 25 different transient groups of killer whales were observed. Statistical analysis of the gathered information (Kruscal Wallis test) revealed an interesting pattern.

It was observed that a significant difference existed in the frequency of the pulsed calls between the two ecotypes. The resident killer whales produced.34 calls per member per minute while the transient whales averaged only.05 pulsed calls per minute per whale. It was also noted that the transient whales produced.27 calls per whale per minute after a successful kill (during milling) clearly indicating that reduced acoustic communication during foraging and before a kill is an adaptive behavior against alerting mammalian prey which are better equipped to detect the pulsed calls. The comparatively higher acoustic action of the resident whales during foraging is because the salmon fish, which is their favorite prey, cannot sense the pulsed calls. Thus this research confirmed the hypothesis that adaptations in communicative vocalizations in the transient whales are aimed at reducing the eavesdropping and escaping potential of mammalian prey. [Volker et.al, 2004]

Benitez et.al (2005) analyzed the echolocation behavior from the observations of southern resident killer whales along the Salish Sea and the Straight of Juan de fuca in the U.S. And Canadian waters. This research conducted between 4th and 21st Oct 2005, focused on the echolocation and foraging behavior of the southern resident killer whales. A pair of hydrophones were used to record the echolocation clicks. The researchers also observed the echolocation clicks both during the active foraging period and the casual traveling period. Specific characteristics as described in previous research were used to identify either traveling (Barrett-Lennard et.al 1996) or foraging mode (rapid changes in direction, tail lobbing, circling in the same spot, presence of sea birds, etc.). In total ten different recordings were made on as many days. Analysis of one of these recordings (Oct 6th) revealed that a total of 4,162 echolocation licks were made in 10 minutes during the foraging period as opposed to only 155 clicks in a ten-minute period during the traveling mode. It was also confirmed from documentation by visual observation that the rapid echolocation clicks coincided with rapid changes in direction, tail lobbing, circling in the same spot, presence of sea birds suggesting the use of echolocation clicks for foraging. The study confirms that the southern resident killer waves use echolocation as a main tool for foraging and hunting salmon fish. [Benitez et.al (2005)] This research by Benitz et.al attests to the findings from the previous research that killer whales condition their vocal behavior as an adaptive response.

Echolocation in Prey Choice recent research has shown that Killer whales not only use echolocation for identifying potential prey but also to structurally differentiate between them helping them identify their prey of choice. The researchers observed the resident killer whales in the waters of British Columbia and the Washington state, which seemed to exhibit a very strong preference for one particular and relatively rare variety of salmon fish, namely the Chinook salmon. What prompted the interests of the researchers was this selectivity of the killer whales which seemed to prefer the Chinook over the other salmon varieties even during times when the Chinook salmons were only 5 to 10% of the total salmon population. The researchers did backscatter measurements on the different varieties of salmon fish using echolocation signals from a simulated killer whale. Radiograph measurements were also recorded for the three different fish specimen used in the study. The results from the study showed that the echo structures from the different species of similarly sized salmons were very different. This indicates that killer whales, using their echolocation system are able to easily differentiate between the three different species of salmons and choose their favorite Chinook salmon without any problems. [Whitlow WL AU, 2008]

Acoustic Pollution and Whale Displacement

Some studies have focused on the effects of acoustic pollution on whale habitats. This study by Morton et.al (2002) observed the population density of killer whales in the Johnstone Strait and the adjacent Broughton Archipelago from 1985 till 2000. The study region was constantly monitored using seven remote hydrophones and from strategically located observation vessels. All the hydrophones were connected to a radio transmitter that facilitated the study of the signals at the research center. An average of 1000 hours of recording was available every year. Similarly a 32 square miles region of the Archipelago was acoustically monitored. Acoustic harassment devices were deployed in strategic locations along the archipelago and their output constantly monitored by portable hydrophones. Between the years of 1994 and 1999 when the AHD were operating, the killer whale population was estimated both in the Johnstone strait as well as the archipelago. It was found that there was no significant change in the whale sightings along the strait (mean=192.40, s.d.=8.26, n=5) while it was considerably reduced along the archipelago where the AHD was in operation mean=9.80, s.d.=4.97, n=5) clearly indicating the negative effects of the aquatic harassment devices. Though the exact cause for the displacement of the whales is not ascertained it is believed that the interference of the high amplitude signals from the acoustic harassment devices could have caused a masking effect on the killer whales communication system disrupting their routines. [Morton et.al (2002)]

Conclusion

Killer whales communicate among themselves and their environment using a wide variety of sounds produced from their nasal sacs. These distinct noises known as dialects are almost unique for a particular pod of the killer whales. Using the whistles, low-pulsed noises and echolocation, Killer whales have developed effective foraging, hunting and social skills that are vital for their survival. From the literature that we have reviewed it is clear that environmental pollution and marine acoustic pollution can have serious implications for the lives of killer whales. The growing aquaculture industry and the use of aquatic harassment devices to enhance fishing profits across the oceans poses a serious threat to the whales and some other marine mammals. It is also clear that there is going to be a steady increase in marine noise pollution due to the growth in marine traffic and increase in oceanographic experiments in the future.

The consequences of such uncontrolled development for the killer whales and other marine species are certainly not good. With positive evidence from many researches indicating the importance of vocal communication for the survival of killer whales and other marine mammals it is imperative upon us to take steps to ensure that their natural survival mechanisms are not trodden over by man made interferences. Creating such awareness is the responsibility of every marine biologist as maintenance of the ocean ecosystem is critical for our own environmental balance.