Watching some House Finches last weekend, it occurred to me that many
smaller species of bird have an undulating flight while larger birds tend to
fly in a straight line. Why is this?

I assume undulating flight consumes less energy than flying in a straight
line. However, this advantage must diminish with increased weight which is
why woodpeckers are about the largest bird to use undulating flight.

How is undulating flight more efficient for a small bird?

Hmmmmmmm.

John.

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