...The researchers say that free-roaming dogs (ones without an owner or otherwise left to run free) are thought to account for about 75 percent of the global dog population, and their interactions with other animals can be problematic.
...In the late 1980s, researchers found that a single German shepherd on the loose in New Zealand's Waitangi State Forest was responsible for killing up to 500 kiwis. The dog had a collar, but was unregistered, and its owner was not found.
...In another example from 2006, 12 ownerless dogs were thought to be wiping out populations of the endangered Fijian ground frog on the tiny Viwa Island. The Fijian villagers' solution was to "befriend" the dogs by feeding them scraps of food. Ten of the canines were eventually tamed and shipped off the island and the remaining two were killed.
...I have posted about how I had to hunt feral dog because they had taken down 2 newborn calves. With people kept dumping off the dogs, I ended up killing more than 45 that were someone's pets a short time before. It is something that I wish that I did not HAVE to do. It still sickens me.
the rest of the story can be read from the link below.