5 Dog bark (Csaba Molnár’s recording) 

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... on location (Tooze et al. 1990 ). Due to their acoustic structure, howls can travel long distances without severe distortion and hence the information content remains reliably preserved. According to Nowak et al. ( 2006 ), the spontaneous howling activity of wolves peaks between July and October, during the season when pups were present. Most of the howls were recorded during dusk and they were emitted from the core area of the territory, and it seems that they mainly serve as long range contact maintenance between pack members (Nowak et al. 2006 ). Tooze et al. ( 1990 ) found that the fundamental frequency, particularly its variability, makes howls individually distinctive. Fundamental frequency also carries information about the maturation status of the individual: adults’ howls have lower fundamental frequency than juveniles’ howls (Harrington and Mech 1978 ), and unfamiliar packs seem to react only to howls from adult individuals (Harrington 1986 ). However, it still remains an open question whether wolves can use this information during communication and recognize or discriminate each other by howls. Between groups, howls seem to play a role in territory defence, communicating location and advertisement of resource ownership (Harrington and Mech 1979 ). When humans mimic howls within the territory simulating a single stranger tres- passing, the pack’s reaction can range from silent avoidance to howling back and approaching the intruder, depending on multiple factors (Harrington and Mech 1979 ). For example, the breeding season and presence of young individuals can heighten the probability of howling and approach, either if the pack is around a fresh kill or assembly sites of the pack (rendezvous sites). Social status and pack size is also important, as larger packs and packs in the presence of the alpha individual respond more readily than smaller pack in the absence of the alpha (Harrington and Mech 1979 ). All these observations suggest the packs attempt to avoid any confrontation that can be costly or even lethal, unless they have to defend high value resources. In these cases, wolf packs often howl back revealing their position and try to search for and probably physically repel the intruder. In such situations, cues to physical strength and inner state represented in the howls could play a crucial role in preventing actual confrontations. Single howls can probably convey both types of information. On the one hand, howl length is associated with body size providing information about the resource holding potential of the individual (Harrington and Mech 1978 ), while tonality and frequency are both affected by the inner state of the wolves: the closer wolves approach an intruder, the lower the fundamental frequency and tonality of their howls (Harrington 1987 ). This acoustic change with inner state seems to closely follow Morton’s structural motivational rules (Morton 1977 ). Interestingly, group howls seems to conceal the real size of the pack: for humans, the number of howling individuals is hard to estimate or measure by listening or analysing choruses. Probably the raising variability of the fundamental over the chorusing and the abrupt changes cause the so called “Beaue geste” effect providing an interesting example of potential information withholding (Harrington 1989 ). Recent fi ndings also demonstrate that, whilst the number of individuals howling may be unclear, there can be recognizable group specifi c cues (mainly fundamental frequency and variance components and duration) in chorus howls (Zaccaroni et al. 2012 ). Such information likely facilitates the recognition of neigh- bouring packs, and extraction of up-to-date information regarding location. The most prominent feature of barks are their short durations (0.2–0.6 s) and spectral shape that resembles a ‘Christmas tree’ formation due to the progressive lowering of energy in higher frequencies (Feddersen-Petersen 2000 ). Barks possess variable fundamental frequencies (150–900 Hz) and noisiness, and in structure they show a typical curved shape with fast raise and drop in frequency. Barks can be emitted as single calls or bouts. Several subtypes can be recognized, which are sometimes classifi ed as different calls, but, as with the whines and howls previously described, we suggest that subtypes just represent extreme variants of barks. The most tonal barks with the highest frequency (above 400 Hz) are referred to as yelps (Cohen and Fox 1976 ; Schassburger 1993 ), which have been suggested to develop from whines by temporal shortening. At the other side of the range stands the woof (or cough), which has low fundamental frequency (90–120 Hz) and is noisy, produced by a short (0.1–0.15 s) burst of air emitted through closed or slightly open mouth and can be an intermittent form between barks and growls. Finally, real barks are noisy, loud bursts, with a medium fundamental frequency (150–170 Hz) falling between yelps and woofs (Fig. 4.5 ). In wolves, barks and woofs are used primarily in threat contexts, such as territorial defence or dominance interactions, while yelps occur more in fearful situations and are used relatively infrequently (Schassburger 1993 ). This contrasts substantially with the vocal behaviour of dogs, which bark basically in any social context (Cohen and Fox 1976 ). This phenomenon has of course prompted many researchers to investigate this obvious discrepancy. Bleicher ( 1963 ) suggested that dog barks are just non- communicative bursts of excitement and Cohen and Fox ( 1976 ) argued that barks became hypertrophied during domestication due to the relaxation of selection pressure for silence. However, Cohen and Fox also emphasize that humans would prefer dogs during selection which provide information with their barks, but also suggest that selection towards high contextual specifi city is unlikely. If the latter is true, barks should have gradually lost their communicative role (Coppinger and Feinstein 1991 ). Boitani and Ciucci ( 1995 ) fi ndings show that feral dogs also use barks in similarly limited number of contexts as wolves supporting the relaxation hypothesis. By studying and comparing the acoustic structure of dog barks with other mammalian and bird vocalizations, Lord et al. ( 2009 ) raised the possibility that barks originally functioned as mobbing signals to threaten intruders and assemble pack members to protect their territory. They suggest that the hypertrophy of barks is due to the shrink of dogs’ living area and the continuous disturbances in the human environment. Another possible scenario is that during domestication barks were released from selective pressures and became more prominent. Later, due to the selective breeding by humans who preferred more communicative and understandable dogs, barks diversifi ed to provide inner state information (Pongrácz et al. 2010 ) as well as contextual information (Tembrock 1976 ). This idea is supported by recent fi ndings demonstrating that dog barks show specifi c contextual differences (Feddersen- Petersen 2000 ; Yin 2002 ; Yin and McCowan 2004 ). Moreover, it also appears that humans can categorize dog barks by their context surprisingly well and are able to assess their probable inner state (Pongrácz et al. 2005 ). For example, humans could discriminate dog barks recorded from situations when a stranger approached the household, before walks, when left alone or during play, irrespective of whether they owned a dog or not. Also they assigned aggressive inner state to barks recorded from agonistic contexts, happy inner states to playful contexts and fearful inner states to stressed contexts like separation from the owner. In a similar way to howls, barks conform to Morton’s rules and humans apparently use their frequency, tonality and rhythm to recognize the dogs’ inner states (Pongrácz et al. 2006 ). Further studies showed that dogs can also discriminate barks recorded from different contexts, and dogs can also differentiate between different barking individuals suggesting that these calls might convey specifi c identity information (Molnár et al. 2009 ). In spite of this, humans could not differentiate individual dogs by their barks, nor could owners recognize the bark of their own dog when confronted with barks of other individuals of the same breed (Molnár et al. 2006 ). Although there is a growing body of research on dog barks, it is important to highlight that only by directly comparing barking behaviour between dogs and wolves, and thorough acoustic analysis of barks from both species will it be possible to unpack why and how this interesting difference in their vocal behaviour emerged. Grunts are low frequency (85–200 Hz), short, harmonic or slightly noisy calls of wolf and dog pups (Cohen and Fox 1976 ) emitted during relief, comfort or pleasure. In dogs, they are also present in adulthood (Bleicher 1963 ). Our personal observations showed that they occur during scratching or petting by humans, especially in greeting situation, raising the possibility that this call is a paedomorphic relic, but further investigations would be necessary to support this hypothesis (Fig. 4.6 ). Groans are spectrally and acoustically similar to moans. They have a relatively low or medium fundamental frequency (250–450 Hz) modulated periodically, with low level of spectral noise. These calls are emitted by dog pups and adults in acute distress, pain or sickness (Bleicher 1963 ), but mentioned by Cohen and Fox ( 1976 ) as general canid vocalization too. Growl vocalisations are generally elongated, broadband, low frequency (80–300 Hz) vocalizations with low frequency modulation and a high concentration of noise but still with a visible harmonic structure (Riede and Fitch 1999 ). Due to their low amplitude, growls are used only as short-range signals. On a behavioural level, two types are distinguished: the snort , which is the nasal form of the growl, emitted ...