In Hawaii, the growth of feral cat colonies is endangering Hawaii’s indigenous birds, marine animals and other native wildlife through toxoplasmosis, which is spread through the cat’s feces. Cats are the only known reproductive host of the toxoplasmosis parasite. 

Toxoplasmosis is a disease caused by the parasite toxoplasma gondii. It enters the environment when its eggs are shed through the feces of cats. Billions of eggs can be dispersed into the environment from just one cat over a two-week period of infection, and the eggs remain alive and infectious for months to years after they leave the cat.

Angela Amlin, Hawaiian Monk Seal Recovery coordinator at the National Oceanic and Atmospheric Administration (NOAA), said the increase in feral cat populations has had a direct effect on the increasing number of cases involving monk seals, Hawaiian coots, ducks and booby birds.

“We currently estimate the amount of feral cats on Oahu alone are anywhere from 50,000 to 300,000,” said Amlin. “The primary thing that people can do to help is keep pet cats indoors and not to abandon unwanted cats or kittens outdoors or at feral cat colonies.”

NOAA fisheries shared the unfortunate news that three female monk seals were found dead between May 15-17 on Oahu. This revelation brings the known monk seal mortalities from toxoplasmosis to 11.

The disease is also responsible for killing native birds like the alala and nene in the terrestrial environment. The parasite can also be washed downstream by rainfall and flow into the near-shore environment, where they infect monk seals as well as spinner dolphins. Cats that roam and defecate outdoors in any part of the island ecosystem can become carriers and spreaders, and ultimately cause the death of native wildlife.

Given that not all deceased seals are recovered for examination, it is likely the reported mortality numbers from toxoplasmosis are higher, as more mortalities have likely gone undetected. 

Amlin added that a trend is emerging wherein female seals are disproportionately affected compared to males. 

“This exacerbates the impact on the entire species,” she said, “as each female seal lost to the population means that all of her potential future offspring are lost as well.”

For more information, visit the Centers for Disease Control and Prevention website at www.cdc.gov/parasites/toxoplasmosis/ or email any questions to monksealinfo@noaa.gov.

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