Question: Last week, I saw a locally produced PSA on TV about rat lungworm disease, and the importance of eliminating rats where ever we find them. Whose kuleana would it be to eradicate the rat population in Makiki Stream, which runs along Kalakaua Avenue up to King Street? I’ve been feeding daily a mated pair of beautiful Muscovy ducks in that stream, and as many as five big, fat rats at a time show up in broad daylight to snatch the food. It’s disgusting even to the ducks. The rats swim with the food across the stream to probably another of their lairs. I suspect that the rats had swiped recently laid duck eggs. Yes, I know that the distinctive and handsome Muscovy ducks deserve a better home. Would there be anyone who would adopt them? …

Answer: Rats are among the worst of Hawaii’s invasive species, destroying crops and property, killing birds, transmitting diseases such as leptospirosis, murine typhus and salmonella, and shedding in their feces the parasite that causes rat lungworm disease, with its potentially serious neurological effects, health and wildlife authorities say.

Hawaii has three main rat species. The roof rat or black rat (Rattus rattus) has displaced the Norway rat (Rattus norvegicus) as the species most commonly found near human habitation, especially in wet areas such as stream beds, drainage canals and sewers, according to the U.S. Fish and Wildlife Service. These rats can climb trees, telephone poles and brick walls; walk across utility lines, squeeze through tiny holes and swim for a mile, it says.

(Hawaii also is home to the Pacific or Polynesian rat (Rattus exulans), but that species is smaller and more commonly found in fields than in urban areas.)

Rats are nocturnal; that you are seeing apparently healthy rats during the day may signal a major infestation. You asked about kuleana, or whose responsibility it is to eradicate rats outdoors in that stretch of town.

Neither the city nor state governments has a vector-control team assigned to that task. There are too many rats on Oahu to get rid of them all, so the health department focuses on situations that threaten public health, said Grace Simmons, environmental health program manager for its Vector Control Branch. “Unfortunately, we are not able to control these rodents at an island-wide level. However, through public education campaigns and partnerships with community groups, we believe we can suppress their populations to help prevent cases of infectious disease,” she said.

Ross Sasamura, director of the city’s Department of Facility Maintenance, which oversees streams on city property, said the city “does not have any agency with resources to address this matter.” In the past, the department has gotten help from the state vector branch to control rats at the Ala Wai Canal, he said. Makiki Stream is east of Kalakaua Avenue, running parallel from Makiki to the Ala Wai Canal promenade.

One thing you can do to help: Stop feeding the ducks. Although it’s not your intention, you’re also feeding the rats. The same is true of anyone else on the island who leaves food outdoors, unattended, for a prolonged period.

Removing food attractants is key to permanently reducing rat populations, according to the health department. Common attractants include exposed garbage; food left outside for pets or for feral or wild animals, including in bird feeders; and fruit or nuts that have fallen from trees.

Over the years, community groups have cleaned Makiki Stream numerous times, removing tons of junk and making the area less hospitable to vermin. We’ll follow up to see whether another cleanup is scheduled soon.

As for the ducks, we learned from Hawaii Birding Trails (808ne.ws/muscovy) that this mostly black- and white-feathered species with red or pink wattles is native to the tropics of Mexico and Central and South America. You said in a subsequent email that you believe this pair to be abandoned pets, and that you aren’t the only person tossing food down to them, because you want them to survive.

Write to Kokua Line at Honolulu Star-Advertiser, 7 Waterfront Plaza, Suite 210, 500 Ala Moana Blvd., Honolulu 96813; call 529-4773; fax 529-4750; or email kokualine@staradvertiser.com.