Plus-Hex CLINICAL and people . Personal odours can change over time , which is likely to be why familiar dogs will still sniff each other regularly [ 3 ] . Research has also demonstrated the ability of dogs to recognise human emotional feeling from someone ' s unique scent alone [ 7 ] , enabling them to detect human anxiety and fear .
Dogs can also communicate through the strategic depositing of urine and faeces , which leave olfactory messages and visual markers within the environment [ 8 ] . Owing to the influence of dog owners on toileting behaviour , understanding urine-specific communication is challenging , but it does seem to be affected by range . For example , it is well evidenced that the urine of an in-season female dog is attractive to entire male dogs , but a male displays increased interest when the urine is deposited within close range of its home [ 9 ] .
Barking is the most typical vocalisation made by dogs , and is generally performed in short-range interactions such as greeting , warning , frustration and attentionseeking [ 19 ] . The pitch , pattern , frequency and volume of the bark , as well as the accompanying body language , can be used by veterinary professionals to help identify why a dog is barking ( Figure 2 ). For example , frustration in dogs is generally expressed through a high-pitched , explosive burst of barking .
It is also believed that dogs can see urine trails – even once they have dried and are no longer visible to the human eye – due to significant visual acuity at lower light levels , particularly in the ultraviolet spectrum [ 10 ] . This most likely evolved as an aid to hunting prey animals at dusk , coupled with the greater ability of dogs to detect movement rather than focus on stationary objects or those within very close range [ 11 ] .
Dogs can also shed their hair , skin cells and saliva into the environment – all of which are detectable by other dogs . This may be circumstantial , occurring as the dog ' s body moves through the environment , or deliberate , such as a dog rubbing against a person or piece of furniture ; this is an area for further research . The transfer of scent relating to specific emotions , such as fearfulness , might also occur involuntarily [ 12 ] – for example , piloerection can occur naturally as part of the stress response and could release scent – but this scent still provides information that is detectable by other dogs .
Sound and vocalisation
Hearing ability in dogs evolved primarily to optimise hunting , with each ear able to work independently to locate the direction and source of sounds [ 13 ] . Dogs can detect high-frequency sounds , such as small rodent prey , way beyond human detection , although their hearing is similar to that of humans at lower frequencies [ 2 ] .
Dogs also have a rich vocal repertoire [ 14 ] comprising a variety of sounds from panting and sneezing to whining , growling , barking and howling . This repertoire appears to have been enhanced through domestication , to aid communication with humans [ 15 ] . Just like humans , dogs can be individually recognised by their unique ‘ voice ’ [ 16 ] . However , sounds made by individual dogs will vary depending on the context in which they are made . Growls have been identified as conveying information about the growling dog ' s size , perceived physical ability and intentions [ 17 ] , and a playful growl will differ from a fearful growl [ 18 ] .
Figure 2 . A dog barking in its hospital kennel .
Conversely , howling is believed to be a long-range form of communication , aimed at reunification and eliciting group ‘ togetherness ’ [ 19 ] . Whining commonly indicates stressful arousal , but might also be performed during greetings [ 20 ] . Yelping is attributed to acute pain , whereas grunting – sometimes performed by dogs when enjoying a face rub from a trusted human – is thought to express pleasure [ 19 ] .
Being able to interpret emotional expression through vocalisation enables dogs to evaluate the intention of another dog or a human within any potential interaction – or the desire to avoid interaction altogether – whether in or out of sight [ 21 ] . Vocal communication is therefore an essential factor in safety and survival .
Volume 39 ( 5 ) • October 2024
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