Tinbergen’s Four Questions Regarding Orca Behaviour
The type of communication used to transmit information is closely related to the animal’s lifestyle and environment. This can be seen in most terrestrial mammals which are nocturnal so use olfactory and auditory which work as well in the dark as they do during the day. Visual communication would be relatively ineffective in this lifestyle. In contrast humans are diurnal and use primarily visual and auditory signals for communication, but miss many chemical cues which many other mammals base their behaviour upon.
Marine mammals often need to communicate great distances, and the water does not support visual cues over great distance. This is why whales and dolphins use primarily auditory signals. Auditory signals can travel great distances and travel four and a half times faster in water than in air (Ford, 1984). Killer whales or Orca (Orcinus orca) are very social dolphins and live in pods often consisting of family members from between four up to fifty for residential whales while transient pods normally are only between two and five animals (Ford, 1989).
These pods communicate with each other by use of echolocation clicks, tonal whistles and pulsed calls (Deecke et al. , 2000). The three main noises have very different uses from each other. Clicks can either be produced as a single click or produced in rapid succession. Single clicks are generally used for navigation and collection of clicks and whistles are thought to be used for communication amongst members of the pod. Pulses are believed, with the assistance of single clicks, to be the method used by orcas to distinguish objects and discriminate prey (Barrett-Lennard et al. 1996). Residential orcas feed on fish, and can be frequently heard communicating with the clicks, whistles and calls because the fish have very poor hearing abilities (Wilson, 2002). The vocal behaviour of transient killer whales is quite different with the vocal communication consisting of occasional clicks and pulses (Deecke et al. , 2000). The only occasion where transient orcas display significant amounts of vocal activity is when they are active on the surface or recently after a kill.
The reasons for this reduction of noise could be due to many factors which can be seen in other species interactions and behaviour. Using ‘Tinbergen’s four questions’, I will explain what necessity for this behaviour and what the origins of the silent behaviour may have been. Tinbergen’s Four Questions In 1963 Nikolaas Tinbergen published a paper “On aims and methods of ethology”. In this paper he discussed how he believed any question regarding animal behaviour should be broken down into four different questions.
These four questions could be divided into two categories, evolutionary (ultimate) explanations and proximate explanations. The evolutionary explanations, which refer to the population, include evolution or phylogenetic determinants and survival value or adaptive significance. The phylogenetic determinants refer to all evolutionary explanations which are not covered by adaptive significance. These may include random processes including mutation and changes in the environment which could have impacts on the population resulting in a specific behaviour adaptation.
The adaptive significance closely follows Charles Darwin’s work on natural selection where it is explained that an animal’s form has been altered to function better in the habitat and resulting in a increase in fitness for the individual. The proximate explanations are focused with dealing in terms of the individual as opposed to the population. The two different individual questions proposed by Tinbergen relate to causation and ontogeny. The causation for a display of behaviour relates to the mechanics of the body and which stimuli provides a cue for the animal to display this behaviour.
Included in causation is control of hormones, motor control, central-nervous-system control and the ability to process the information obtained through senses. Ontogeny relates to the development of an individual, from conception til death. This may include a experience or a environmental factor which occurs and changes the behaviour of the animal, including learned behaviour from another individual. Causation ? Figure 1: An illustration of sound generation, propagation and reception in a killer whale. (WhalesB. C. com)
The nasopharyngeal anatomy of cetaceans is strongly modified comparing with terrestrial mammals. They have one impair respiratory hole at the top of the head. It is closed near the surface by dense musculocutaneous crimps arranged so, that the salient of one of them enters into the dimple of another. They form a peculiar lock preventing the water from penetrating into respiratory tract. Above the skull around of nose passage there is a system of pneumatic sacs, connected with nose passage (Barrett-Lennard et al. , 1996).
In 1964 A. V. Jablokov supposed that sounds could be produced by forcing air through these nasal sacs. Air is forced past a set of finely striated muscular plugs or lips that vibrate or slap against each other as the lips are forced apart by the stream of air and then slapped shut by muscular tension (Ford, 1989). Transient killer whales are often very difficult to track when under water as they are typically silent. Often communicating with each other with just a single click, known as a cryptic click (Deecke et al. , 2000).
The only time that the killer whales produce large amounts of vocal activity was when milling about on the surface or after killing a marine mammal. Transients have been found to only use four to six discrete calls which are not shared with the resident pods (Deecke et al. , 2004). Ontogeny Like other aspects of learning in mammalian society, I hypothesise that the newborn calves will be taught the ability for vocalisation by its parent or other pod members. There have been many studies on killer whale vocalisations in different parts of the world including Canada (Ford, 1984), Alaska (Yurk et al. 2002) and Norway (Matkin, 1988). Each study showed that every pod has its own distinctive repertoire of discrete calls, often this phenomenon is referred to as vocal dialects. The differences in vocal repertoires can be the result of geographic isolation and when this occurs it is not dialects that are being represented but “geographic variations of vocal repertoire” (Ford, 1984). The use of repetitive calls and the specific number and type of discrete calls are what are used to classify and compare dialects. Pods often produce between seven and seventeen different types of discrete calls.
Some pods share calls and are grouped together as a acoustic clan (Baird et al. , 1988). Different clans might represent different independent maternal lineages, which have persisted for many generations, developing their independent call traditions. Dialects are probably the means by which pod cohesiveness and identity are maintained. Newborn calls manage to produce calls very comparable to their mothers, but the repertoire is very limited. With the arrival of a new calf to the pod, the calls of the pod and particularly the matriarch increase, especially the frequency of pod-specific calls (Ford, 1989).
This is widely regarded as the method to which newborns learn the pods dialect. The majority of the learning done by the newborn is a process of imitation and trial and error. The calf does not always learn communication from a parent. In captivity a young whale was observed to have learned the calls of its tank mate, even though it had no relatedness. Survival Value I hypothesise that the because the mammalian predators can hear well under water is the reason why the transient killer whales adopt significantly reduced communication during periods of foraging.
Acoustic communication can have great benefits such as organising groups for attacks and avoiding predation. As with all behaviour traits there is a trade off. There is a direct cost of energy required to producing the sounds and along with this is the loss of energy from lack of feeding during times of communicating. There is also a indirect cost, especially for transient killer whales, which pass information on to eavesdroppers. Eavesdroppers may include competitors (Hammond et al. , 2003), predators (Hosken et al. 1994) or for transient killer whales alerting potential prey. Various studies have documented the costs from eavesdropping for prey in the case of predators who utilise echolocation. Bats have been documented preying on frogs performing mating calls by eavesdropping on them (Fenton, 2003). Insects have also been noted as being able to avoid predation from bats by listening to their acoustic projections (Rydell et al. , 1995). Communicative vocalizations are usually not essential for prey location unlike echolocation.
This is the most likely reason that transient killer whales move in silence or considerably reduced vocal communication while foraging. Evolution I believe that the evolution of marine mammals from a common ancestor hinders the transient killer whales hunting due to the retention of excellent underwater hearing by marine mammals. In Pakistan the discovery of Ambulocetus was remarkable, a three metre long mammal which resembled a crocodile. It is thought to be the transitional fossil starting the mammalian movement towards an aquatic life.
By 38 million years ago mammals had fully adapted to a aquatic life with the emergence of Basilosaurus and Dorudon. Although these large marine mammals resembled modern whales and dolphins they lacked the ‘melon organ’ which allows echolocation in their descendants (Ford, et al. , 2000). In the middle of the Oligocene (33 million years ago) a animal called Squalodon is thought to have been the first to use echolocation. With a cranium which was well compressed, and a telescoped rostrum it displayed a skull similar to modern dolphins.
A big problem with the hunting marine mammals is that they all have a common ancestor, and all have retained a common lineage of very good hearing. Fish have poor hearing which allows the residential killer whales to freely use communication when hunting. Transient killer whales have been forced to change this behaviour because of their choice of prey including seals, dolphins, porpoises and whales. With all mammals having good underwater hearing they have been required to adopt a reduced vocal communication when searching for prey. Conclusion
I believe that the lack of acoustic communication between transient killer whales is due to the ability of their selected prey being able to hear the clicks, whistles and pulses they generate. These sounds can be heard from over seven kilometres away and marine mammals do react to these calls (Deecke et al. , 2002). In the study by Deecke in 2002, he played the sounds of killer whales near a harbour seal colony which resulted in most of the seals displaying strong anti-predator behaviour of leaving the water. This suggests that they are able to clearly hear the calls and understand what is generating them.
I believe that other marine mammals will react in a similar way. Guinet (1992) observed the vocal patterns of killer whales around the Crozet Archipelago and came to the same result as Deecke (2004) that the killer whales were silent throughout hunting and searching, but once a mammalian kill was made the pod would greatly increase in vocal activity. While it can be a risk to produce noise after killing a prey, for fear of drawing the attention of other predators or scavengers, killer whales are the apex predator and have no natural predators.