In late May 2014, in my garden on Scilly, I was watching a Goldfinch Carduelis carduelis on a niger feeder that I had constructed from a plastic bottle. To my great surprise I then heard what seemed to be a Great Spotted Woodpecker drumming – Great Spots are a major rarity on Scilly, with fewer than 20 records. But no woodpecker was seen, just the Goldfinch pecking at the bottle, and seemingly at a relatively leisurely pace, although very vigorously. But drumming noise and feeding action of the Goldfinch were synchronised.
It transpired that as the feeder became depleted the bottle began to act like a sounding board, amplifying the noise made by the bird’s bill while attacking the seed. Without the noise you could not detect any movement of the bill other than a single thrust to get a seed, but within that thrust there must be several movements, maybe helping to split the niger seed and extricate it from the hole.
An alternative reason, supplied by a fellow local birdwatcher Martin Goodey, who has observed the same action, is that the seeds form a ‘cave’ at the feeding hole and the Goldfinch has learnt that drumming dislodges the seeds and helps extricate them.
A video of this can be seen here:
It would be interesting to know whether others have also encountered such behaviour.
Nigel Hudson, St Mary’s