Abstract

In April 2017, USFWS and wildlife rehabilitation centers along the California coast south of Santa Barbara began receiving reports of large numbers of loons and smaller numbers of other species of aquatic birds live-stranding and dying on beaches in Oxnard and Ventura, California. Live-stranded birds were transported to International Bird Rescue’s Los Angeles Wildlife Center (IBR) for care. Between April 4 and May 30, 121 live birds were received, including 83 Pacific Loons (Gavia pacifica), 25 Red-throated Loons (Gavia stellata), nine Common Loons (Gavia immer), three California Brown Pelicans (Pelecanus occidentalis californicus), and one Western Grebe (Aechmophorus occidentalis). Admissions peaked during the week of April 16–22. Domoic acid (DA) was confirmed as the cause of the event by multiple testing facilities. Clinical signs exhibited by affected birds were generally quite mild. Most birds appeared to be disoriented with reduced mentation, and would sit quietly with minimal struggle (which is quite abnormal for loons). Only nine birds showed neurologic clinical signs such as head twitching, whole body tremors, ataxia, or seizures; one Pacific Loon was hyper-aggressive to conspecifics. Four of 24 live birds tested for DA returned positive blood samples, but only one of those four showed notable neurologic signs. Twenty-three birds were euthanized or died in the first 24h of care. Surviving birds had minimal problems attaining waterproof plumage, and excellent appetites throughout care. Those that entered care emaciated quickly regained lost mass. Behaviorally, many birds remained obtunded for days to weeks despite self-feeding and maintaining waterproof plumage while housed in pools. Later, it was difficult to assess if birds had recovered because in many cases birds appeared clinically normal when in hand, having normal body weight and blood values and relatively loon-normal attitudes, but in pools, behavior was often abnormal. The most-affected birds would float quietly and drift in pool current, often with fluffed neck feathers and subdued demeanor. We decided to keep birds for at least two weeks, and then begin assessing for release. Release criteria included normal physical exam, packed cell volume >40%, and normal active/interactive behavior with conspecifics in pools as judged subjectively by experienced loon rehabilitators. Fifty-one birds were federally banded and released, 47 were euthanized. To avoid releasing the survivors into ongoing HAB zones within the Southern California Bight, most were released in groups in Morro Bay 140 miles (225 km) north of Ventura. In a previous toxicity study, Common Murres (Uria aalge) dosed intracoelomically with domoic acid showed only mild effects including hypothermia, abducted wing carriage with decreased mobility and responsiveness; no histologic changes to the brain were found1. In order to characterize changes to avian brain with more chronic exposure to DA, the brains of six loons euthanized at IBR due to long term obtundation were collected for histology. The last remaining bird from the event was euthanized and necropsied after 100 days. No gross lesions were noted save for an atrophied appearance to the brain, with fluid occupying a large proportion of the subdural space in both hemispheres. Histology is pending.

Acknowledgements

The authors wish to thank wildlife rehabilitators from Santa Barbara Wildlife Care Network, Camarillo Wildlife Rehabilitation, and California Wildlife Center for rescuing, stabilizing, and transporting birds to IBR, staff and students from David Caron’s lab at University of Southern California for running DA samples, plus Lena Chang and Jenny Marek from the Ventura office of U.S. Fish and Wildlife Service for their tremendous work during this event.

* Presenting author

Literature Cited

1.  Silvagni PA. 2003. Comparative pathology and diagnosis of domoic acid toxicity. PhD dissertation, University of California, Davis. 139.