The Goat-sucker

El Chupacabra translates literally as "the goat-sucker," although the creature hasn't killed a more statistically significant number of goats than it has other livestock.  In fact, the first reported Chupacabra attack in 1995 involved the deaths of eight sheep.  Since the mid-nineties the Chupacabra has been blamed for countless attacks on livestock and other domesticated animals, in areas ranging from Puerto Rico, through Mexico and the southern and southwestern United States.  The attacks tend to happen at night and are thus rarely witnessed.  They are said to be notable for the puncture wounds on the corpses of the Chupacabra's victims, and the lack of blood present at the scene.  

Many skeptics speculate that the creature's modus operandi closely resembles that of more common predators known to threaten livestock, such as coyotes and wild dogs.  These animals often become desperate enough to hunt domesticated animals if they are inflicted with a condition that impedes their normal hunting practices, and in fact, descriptions of the Chupacabra in Mexico and the southwestern United States are consistent with a coyote or dog that has contracted mange.  Eyewitness descriptions from Puerto Rico are rare, but the most famous account described the creature as a bipedal, reptilian monster; a far cry from the mangy coyotes of the mainland.  Again, skeptics are quick to point out that this description seems to closely match that of a monster from a popular science fiction movie of that time, and that the actions of the predator involved still fit the motive of an impeded animal; they believe, too, that many of the more sensational aspects of the attacks, such as the missing blood, could be due to improper investigative techniques used at the scene.

Ultimately, though, that is speculation, and the only thing we can be sure of is that something killed a large number of livestock in Puerto Rico in the mid-nineties, and even if the accounts from other areas can be attributed to mundane animals, that doesn't mean the same thing necessarily happened during the original island reports.  The mystery of the Chupacabra remains, at least for now.