The California tree rat is the same species that carried the bubonic plague in Europe during the Middle Ages. They love to inhabit the dead fronds that hang from Washington and Mexican fan palm trees that have not been trimmed, and which probably remind the rats of the thatched roofs of medieval buildings.
The threat of plague in California comes mainly from ground squirrels and, fortunately, it has not yet spread to rats.
They need our rat snakes and corn snakes.
https://en.wikipedia.org/wiki/Corn_snake
https://en.wikipedia.org/wiki/Rat_snake
“...which probably remind the rats of the thatched roofs of medieval buildings...”
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I doubt that a rat today remembers roofs from long ago.
We lived in LA decades ago. Well, actually in Santa Monica. I don’t think I ever saw a rat.
Rats are having a Population Explosion?