1.https://www.nature.com/articles/ncomms16082
2.https://www.livingwithwolves.org/about-wolves/language
3.http://wolfsongalaska.org/chorus/node/28
4.https://www.tandfonline.com/doi/pdf/10.1080/11250008209439382
5. https://moderndogmagazine.com/articles/perfect-pitch-dogs-music/248
6. https://books.google.com/books?id=gbZXYnE2KlgC&pg=PA246&lpg=PA246&dq=music+that+most+often+causes+dog+to+howl+is+wind+instruments,&source=bl&ots=kOLNH4BBO9&sig=3ptHnRCtBBhuXywrq_STqwYDFk0&hl=en&sa=X&ved=0ahUKEwia8LHhmYHcAhVmHDQIHYhwAAoQ6AEIiAEwBw#v=onepage&q=music%20that%20most%20often%20causes%20dog%20to%20howl%20is%20wind%20instruments%2C&f=false
7.https://www.researchgate.net/publication/233523767_The_influence_of_auditory_stimulation_on_the_behavior_of_dogs_housed_in_a_rescue_shelter
8.https://www.aspca.org/pet-care/dog-care/common-dog-behavior-issues/separation-anxiety
9.https://pets.webmd.com/dogs/guide/howling-dogs#1
10. http://www.presidentialpetmuseum.com/pets/yuki/