Kevin Schafer / Guatemalan black howler monkey (Alouatta pigra) sitting in tree howling, Community Baboon Sanctuary, Belize. Endangered species.

Eric Baccega / Two European grey wolves (Canis lupus) howling in winter landscape, captive. Bayerischerwald National Park, Germany.

Eric Baccega / European grey wolf (Canis lupus) howling in snow covered forest, captive. Bayerischerwald National Park, Germany.

Mark Bowler / Red howler monkey (Alouatta seniculus) howling, captive

Mark Bowler / Red howler monkey (Alouatta seniculus) howling, captive, digitally modified

Angelo Gandolfi / Two European Grey wolves (Canis lupus) one howling, in snow, captive, Bayerisch National Park, Germany

Juan Carlos Munoz / Black howler monkey (Alouatta caraya) female howling, Pantanal NP, Mato Grosso, Brazil Not available for ringtone/wallpaper use.

Tim Fitzharris / Gray Wolf (canis lupus) howling, North America

Tim Fitzharris / Timber Wolf (Canis lupus) pair howling in snow, North America

Tim Fitzharris / Timber Wolf (Canis lupus) pair howling in snow, North America

Gerry Ellis / Timber Wolf (Canis lupus) howling, temperate North America

Jim Brandenburg / Timber Wolf (Canis lupus) howling, Minnesota