Black dog bias is a veterinarian and animal shelter phenomenon in which black dogs are passed over for adoption in favor of lighter-colored animals. Black dog bias is also known as "big black dog syndrome." Shelters often use the term BBD, or big black dog, to describe the type of larger dark-colored mixed-breed typically passed over by adopters.
The phenomenon may be due to a number of factors, including fear stigma against certain breed types, and the fact that large, black dogs are often portrayed as aggressive in film and on television.
Some people believe that during the pet adoption process some potential owners associate the color black with evil or misfortune (similar to the common superstition surrounding black cats), and this bias transfers over to their choice of dog. Additionally, many shelters feature photo profiles of their dogs on the shelter website. Because black dogs do not photograph well, lighter-colored dogs have an advantage with potential adopters browsing the site. A study done by the Los Angeles Animal Services challenges some of these claims, saying that a full 28% of adopted dogs are black. However, the bias theory simply asserts that predominantly dark animals take longer to be adopted than their lighter counterparts, and that large dogs take longer to adopt than small ones.
However, appearance in general does play a role in potential adopters' selection of shelter dogs. In a 2011 study by the ASPCA, appearance was the most frequently cited reason for adopters of both puppies (29 percent) and adult dogs (26 percent).