Band-tailed pigeons arrive on the oak mast at Finley

The acorns I measured on 19 August are ripe now, and the pigeons have found them. Band-tails move to whatever mast is heaviest within a few hundred kilometres, and this ridge is carrying a heavy crop.

Counting a flock that will not sit still

I used a fixed point at the top of the ridge and counted in five-minute scans, taking the highest single count in each scan rather than adding them up. That avoids double-counting a bird that moves between trees.

• 08:05 scan — 24 visible in the six sample oaks.
• 08:25 scan — 41 as the second flock arrived from the south.
• 08:40 scan — 68, and the whole group flushed together and went down to the boundary spring.
• 09:05 — one sharp-shinned hawk crossed the grove at about 6 m, and there were no pigeons in the oaks for the next forty minutes.

Sixty-eight is a good count for this ridge. The largest flock I have recorded here was 140 in September 2022, in an even heavier acorn year.

Why the pigeons leave a heavy crop

A pigeon feeding in an oak canopy takes acorns one at a time and swallows them whole, and it cannot eat where the ground is crawling with yellowjackets. The acorns that fall early and crack open draw wasps within days, which is why the birds work the canopy and then leave, rather than feeding on the ground underneath.

The morning flight to the mineral spring is the other reason they leave. A pigeon feeding mainly on acorns is taking in very little sodium and calcium, and band-tails are known for gathering at mineral springs and salt licks. The spring on the refuge boundary is small, about a metre across, and the whole flock was there by 08:50, drinking in a line along the edge.

Where they come from and where they go

Band-tailed pigeons here are not resident in the way a robin is. They nest in the lowlands in spring, disperse to the mountains in summer, and move to the coast and the valleys when the mast comes in. So a flock on this ridge in early September is a group in transit between two food sources, and the oak crop on this ridge is a stop rather than a destination.

What to check next time

• Count again on 10 September: the flock should have moved on or been replaced.
• Look at the spring edge for feathers and droppings, which would say how often the flock stops there.
• Check the acorns on the ground under the sample trees for pigeon damage as opposed to squirrel damage. Pigeons leave the cap behind, squirrels chew the whole thing.