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NAMMCO 25

Behaviour


Social behaviour

Like many species of toothed whales, pilot whales are highly social animals and usually occur in pods of 10 to 200 whales, with larger pods occurring more rarely. The largest pod caught in the Faroese drive fishery numbered 1200 animals (Zachariasssen 1993, Bloch 1998). Pods ususally comprise animals of all ages and sexes, with adult females outnumbering adult males (Bloch et al. 1993a). Male-only pods and pods consisting mainly of males have been observed however (Desportes et al. 1994a).

All individuals in the pod, including adult males, are related but males tend not to be the fathers of the calves in the pod, and the pods constitute close matrilineal associations (Amos et al. 1991, 1993ab, Anderson 1990, 1993). Investigation in other areas, based on photo-identification and genetic work, confirm the existence of relatively stable pods, like those of killer whales and unlike the fluid groups characteristic of many smaller dolphins (Jefferson et al. 1993, Canadas and Sagarminaga 2000, Ottensmeyer and Whitehead 2003).

Pilot whales are loosely polygynous. During aggregation, males will temporarily leave their pods to mate with females from other pods (Amos et al. 1993b, Andersen and Siegismund 1994). Mating occur reciprocally between pods and there is no evidence of strong male reproductive dominance (Amos et al. 1993a). Individual male may sire several offspring in the same pod (Amos et al. 1991).

Long-finned pilot whales can exhibit highly synchronous breathing and diving behaviour, both during shallow and deep dives, coupled with body contact (Senigaglia and Whitehead 2012, Aoki et al. 2013). As synchronous swimming does not induce saving in locomotion effort, but on the contrary actually entails some locomotion costs, it must have other functions, such as reinforcing social bonds (Aoki et al. 2013). It allows for close proximity and rapid coordinated response of individuals, with the multiple functions such as showing affiliation and reacting to disturbance (Senigaglia et al. 2012).

Pairs of long-finned pilot whales can perform highly synchronous surfacing behaviour, at less than one body length apart (Senigaglia and Whitehead, 2012). This behavioural synchrony can be maintained during deep foraging dives, when pilot whales jointly swim to several hundred meters of depth in search for prey (Aoki et al. 2013). This suggests that long-finned pilot whales employ a social foraging strategy, whereby individuals synchronize their foraging behaviour, although they do not always synchronize their individual dives (Visser 2014, Visser et al. in press). During foraging, groups sometimes break up into smaller and more widely spaced units with a higher degree of milling behaviour (Visser 2014).

 

GD Globi fam NASS95

A group of pilot whales, including a large male and a calf seen during NASS 95. Note the much paler colour of the calf (bottom), the bulbous head of the large male (top) and its dorsal fin very low in profile and with a particularly thick leading edge. Photo: Geneviève Desportes

An original diving and foraging behaviour?

Diving behaviour was studied off the Faroes by equipping pilot whales with satellite-linked time-depth recorders (Heide-Jørgensen et al. 2002, Bloch et al. 2003, Mikkelsen 2008 and pers. com.).

Dives may last op to 18 min to a maximum depth of 852 m. However 60% of the dives lasted less than three minutes and most diving activity occurred at depth of less than 36 m, although the whales were also travelling off the shelf over water depths exceeding 1,500 m. The whales spent 60% of their time above 7 m. This behaviour is similar to that observed in the Mediterranean Sea (Baird et al. 2002). This intermediate diving behaviour, with the animals spending most of their time close to the surface but typically conducting bouts of foraging dives to intermediate depth of 300-600 m was also observed in the Norwegian sea using Dtags (digital tags) (Sivle et al. 2012).

Compared to other similarly-sized odontocetes, the long-finned pilot whale spent a higher proportion of their time at the surface and exhibited less extreme diving in terms of duration and maximum depth of dives. This may be linked with lower dive capability, the use of a foraging niche in the water column requiring less extreme diving and/or a similar foraging behavious as the short-finned pilot whales using deep sprints for catching prey capable of moving fast, such as Todarodes (flying squid). The sprints, which appear to challenge the common view on optimal foraging in breath-holding, deep-diving predators, reflect a high-cost foraging strategy that is necessary to capture high-value, evasive prey (Aguilar de Soto et al. 2008).


Acoustic behaviour

Vocalisations produced by pilot whales incude clicks, whistles and pulse sounds and calls vary with behavioural context (Taruski 1979). Vocalisations are more complex with active behaviour and greater dispersal of the group or more subgroups present, they are simpler with less active behavior, such as resting at the surface. The vocalisations possibly serve to maintain contact and coordinate the movements of the herd (Weilgart and Whitehead 1990, Kok 2012).

You can listen to pilot whale sounds at https://swfsc.noaa.gov/uploadedFiles/Divisions/PRD/Sounds/PilotWhales.wav

 

With a mean frequency of 4480 Hz, the calls of long-finned pilot whales are lower in frequency, longer and of a narrower frequency range than those of the short-finned pilot whales and there are geographical differences (Rendell et al. 1999). Pilot whale clicks are also different in duration (shorter), frequency (higher), and energy distribution than those of killer whales in the same area (Eskesen et al. 2011). Whistles last less than a second and are repeated typically 14-41 times per minutes. Some may act as 'signature-whistles' unique to individual whales (Martin et al. 1990).

 

Adam Li NOAA NMFS SWFSC

A fast swimming long-finned pilot whale. Photo: A. Li, NOAA/NMFS/SWFSC