By Krysta Rogers and Stella McMillin
A few weeks ago, our avian disease specialist, Krysta Rogers, was notified of an ongoing incident in Kern County. A man reported finding two to five dead birds at a time near his bird feeder over a period of weeks. This added up to 30 to 50 birds in total, most of which were mourning doves.
Often, mortality occurring near bird feeders is disease-related. Bird feeders can unnaturally congregate birds, increasing the chances of disease transmission. In particular, mourning doves are highly susceptible to a parasite that causes a disease called Trichomoniasis. This disease can lead to significant mortality of mourning doves; it tends to occur during the spring in doves that visit bird feeders.
However, in this incident a raptor and the neighbor’s dog also had died in the same location and a similar scenario had occurred the previous year. As such, this incident seemed to be more likely related to a toxin, rather than disease.
Our pesticide specialist Stella McMillin became involved to investigate the cause of death. Fortunately, Krysta and Stella were able to examine two doves that died during this incident.
Examining the doves, they found no evidence of disease. However, when they looked in the birds’ crops we found both of them full of the same milo seed-like material. They showed a picture to the Kern County Agricultural Commissioner’s Office who suggested that it appeared to be strychnine bait. So, they submitted the bait and livers from the birds to a diagnostic lab to test for strychnine and the results were positive.
Strychnine is used to control pocket gophers and is only legally applied underground to prevent exposure to non-target wildlife. In this case, unless these doves had been using shovels, it appears that the application was not done properly. Some formulations of strychnine are restricted only to those with applicator’s licenses but others are available to the general public. Sometimes the general public is not aware that “the label is the law” – it is illegal to use a pesticide in a manner not specified by the label. When a pesticide, particularly something toxic to vertebrates like strychnine, is not used properly, it poses a hazard to wildlife, pets and children, so investigation of these cases is important.
Now the difficult part begins – identifying the source of the strychnine and taking action to ensure that this situation does not occur again.
Although this incident was not related to disease, it is a reminder, that bird feeders, hummingbird feeders, and bird bathes, should be thoroughly cleaned at least once a week to reduce the chances of spreading disease.
For more information about how to keep birds healthy at bird feeders visit the National Wildlife Health Center (http://www.nwhc.usgs.gov/publications/fact_sheets/coping_with_diseases_at_birdfeeders.jsp) and Audubon (http://web4.audubon.org/bird/at_home/bird_feeding/feeder_maint.html).