Varied thrushes arrive in the Marys Peak fog

Fog changes how you count birds. At the lower saddle the visibility was about 60 m, and a mixed flock moving through hemlock in that much fog is mostly a set of sounds with occasional birds attached.

Counting by sound

I stood still for 25 minutes and recorded on my phone, then counted the recording back in the car. The flock was 34 birds:

• 12 golden-crowned kinglets, all in the hemlock tips, giving the high thin call continuously.
• 9 chestnut-backed chickadees, mostly below 3 m.
• 6 red-breasted nuthatches, all on trunks, ignoring the canopy entirely.
• 4 varied thrushes, on the ground and in the low branches, giving the single drawn-out whistle and not the song.
• 3 other species I could hear but not identify: two high thin notes and one chatter, left unidentified rather than guessed at.

The thrushes were the point of the visit. They breed in the lowland conifer stands here and move down and coastward in autumn, and the first ones at this elevation usually show up in the last week of September. Their autumn call is one note, held for about a second, and it carries much further in fog than the song would.

The structure of a flock

The flock was not a ball of birds but a set of layers: trunk workers, mid-height foragers and canopy tippers, each doing a different thing in the same two hectares. Nuthatches on the trunks, chickadees in the middle, kinglets at the tips, thrushes on the ground. That layering is why a mixed flock is worth counting as a flock rather than as five species lists — the birds are not competing for the same food.

What to check next time

• Count the same saddle on 11 October and 25 October to get the arrival curve rather than a first date.
• Watch for thrushes below 300 m, which is where they spend the winter here. A bird at 900 m in late September is on its way somewhere lower.
• Note whether the kinglets stay with the chickadees or split off. In my notes from 2024 the two stayed together until the first hard frost.