Country diary: Do feeders bring out aggression in birds? – The Guardian

Wolsingham, Weardale: The quiet, busy siskins I see on the alders could almost be another species from the belligerent ones at the feeder
Barely a breath of wind this morning, but the branches of an alder overhanging the riverbank are shaking. Siskins are feeding on seeds from its small woody cones.
The birds are easily spooked but, as I sit motionless under the tree, they move closer. Soon they are just a few feet away – lively, lithe little finches, black and lime green with mottled streaks on their underside. Marvellously acrobatic, stretching, dangling, twisting this way and that to reach their reward. Never still for a second, endlessly probing with beaks that taper to a point as fine as jewellers’ tweezers, adapted for extracting the tiny woody seeds between the cone scales.
They are quiet, preoccupied with feeding on their own cluster of cones, so different in behaviour from the feisty siskins that have been feasting on our garden bird table all winter. Those are mutually aggressive and constantly challenge greenfinches and tree sparrows for a perch on the feeder containing sunflower kernels. Sometimes violent conflict breaks out. They are so different in demeanour that they could almost be a different species.
Perhaps that is what providing limitless luxury food in a single location does to bird behaviour: it promotes competition and conflict. A siskin needs to collect about 10,000 alder seeds to match its body weight. It must spend most of the daylight hours feeding on its natural food source but can gain the same nutritional benefit in an hour by monopolising a prime position on the sunflower seed feeder.
The birds in the tree in front of me now are closer than ever. For every seed they consume, many more fall on to the muddy strandline of the retreating river. Thousands of alders in this valley produce an abundance of seeds all through winter, each tree bearing more seeds than siskins ever consume. Next winter’s crop is already in its infancy: this spring’s tiny purple cones are already beginning to swell. Another turn in the cycle of seasons.
Siskins and their preferred food source are well matched, but the promise of easy street on garden bird tables reveals an aggressive nature less often seen in the wild.
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