CDFW Finds Starvation to be Primary Cause of Increased Mortalities in California Seabirds

Increase in Seabird Deaths Not Linked to Avian Influenza

The California Department of Fish and Wildlife (CDFW) has been investigating increased reports of debilitated and dead seabirds on California beaches. Of the birds examined, nearly all have been younger birds that are emaciated, sometimes with opportunistic fungal respiratory infection and/or heavy parasitism, or with secondary injuries.

CDFW began receiving reports last fall initially involving Brandt’s cormorants and common murres and have more recently included California brown pelicans along California’s central and southern coasts, roughly Mendocino County south to San Diego County. Additionally, many wildlife rehabilitation facilities have been admitting increased numbers of debilitated cormorants, murres and pelicans.

Avian influenza has not been detected in the 33 Brandt’s cormorants examined to-date by CDFW. Partners have tested an additional 22 cormorants with preliminary detections of avian influenza in only two cormorants collected in early January from San Francisco County. Avian influenza has not been detected in the roughly 34 common murres tested by CDFW and partners. Preliminary detections of avian influenza have been made in only four murres, two collected from San Mateo County in January and February, and two collected in early March from Marin and Santa Cruz counties, respectively. Testing is ongoing for additional birds collected in recent weeks.

Avian influenza H5N1 was first detected in California wild birds in July 2022. Since then, avian influenza activity in wild birds has typically increased during fall migration and winter and then decreased during spring migration and summer. Although avian influenza H5N1 was recently detected in marine mammals along coastal San Mateo County, this current seabird mortality appears to be largely unrelated to avian influenza activity.

Brandt’s cormorants, common murres, and brown pelicans breed on offshore rocks and islands along the coast. Seabird researchers have reported that 2025 was an unusually good reproductive year for these species. An increase in reproduction is often followed by high juvenile mortality. Young seabirds are typically less experienced at catching prey and are less resilient to changes in food resource availability and adverse weather such as severe wind or winter storms.

Wildlife officials will continue to monitor impacted seabirds from affected areas to better determine if other factors begin to contribute to the seabird mortality. For example, Brandt’s cormorants are sometimes impacted by a parasitic infection called Sarcocystis calchasi, and seabirds and marine mammals are periodically impacted by harmful algal blooms like domoic acid.

Officials ask the public not to touch, harass, attempt to feed or take photographs with debilitated seabirds. Do not attempt to remove any fishing lines or embedded fishing hooks from entangled birds.

How Can the Public Help?

Report stranded seabirds:

• Call your local wildlife rehabilitation facility

Report dead seabirds:

• Residents can report dead wildlife to CDFW’s Wildlife Health Laboratory using the mortality reporting form, which helps biologists monitor the event. Please include photos if possible.

Support a local wildlife rehabilitation facility:

Contact a permitted wildlife rehabilitation facility intaking seabirds directly for how best to assist.

Report marine mammals:

• To report a dead, injured or stranded marine mammal in California, call the NOAA Fisheries West Coast Region Stranding Hotline: (866) 767-6114. Information on species and regional stranding contacts may be found on the NOAA Fisheries website.