Hey,
I think the reason you haven't been finding them is because of the season, or where you're looking. They aren't very active in the summer from my experience, and populations in this area are pond/lake breeders as far as i can find. I suppose some populations could breed in slow flowing streams or canals, but i think most populations stick to the ponds.
What i would suggest is finding a small fishless pond that they may breed in, and have a look around. See if you can spot any larvae or adults in the water, and flip some surface cover around it. If you don't find anything, don't give up on that location. As long as a pond is near forest, is not polluted, and doesn't have too many bullfrogs or fish, it should be healthy enough for newts to breed in it.
There is a population right near me that breeds in a marsh, and they migrate twice a year. The second migration occurs in the fall, during a rainy period. Today i found the first little morph of the year, i have it easy because they cross a road to get uphill to surrounding forest. If there is any location near you that has anything similar, i highly recommend checking it out. A road paralleling a pond is an ideal place to find migrating amphibians, and in the process, save them from getting squished by cars.
Anyway, back to the migrating. So the newly morphed juveniles migrate AWAY from the breeding grounds, while the adults migrate TOWARDS the breeding grounds. Though I still haven't figured out why the adults migrate, since they don't breed until the spring. I'm not sure if the adults do this in all populations in the Seattle area, of it its just something that the population near me does.
If there is a pond near you that you can easily walk to or bike to, i would suggest going there after rain and looking for newts around it. If there isn't a path around the stream, the juveniles may be difficult to spot as they are usually not much bigger than 3 inches, so look closely.
The first migration of the year happens in the spring, when the adults migrate to the ponds to breed. This migration is bigger than the fall migration in my experience. Over the last few years, i have been loosely keeping track of weather triggering these migrations, and its pretty basic. The first warm rains of the spring bring them out, so rainy and 48F or warmer. The month that this happens varies, this year it was January, last year it was early February, and two years ago it was late February through early March.
Also, in my experience they prefer to migrate after rain, rather than during it, especially if its raining really hard. Furthermore, i have had very poor success when its windy.
The best time of day to find them in my experience is from noon or a bit later until dusk, and into the night. They seem to avoid moving in the mornings when its colder.
I can have a look on Google Maps and see if i can find any possible breeding locations in the Renton area, and tell you what i found in PM if you want?
I may be forgetting some info, and sorry if this message is sloppily written, it's a bit late
I can try to think of some more info tomorrow.
Hope this helps!
(Attached is a picture of the newly morphed newt found today)
