Tuesday, July 2, 2013

Welcome Swallow luring prey with attenuated outer tail feathers?

An observation of the same Welcome Swallows mentioned in the sub-surface feeding blog was that, while feeding on prey taken from below the water surface, the birds were often seen to adopt a pose that appeared to be used to lure prey to the surface. It cannot be proved that the swallows were attempting to lure prey but it would be worth further study if similar feeding events are witnessed.

The swallows moved from a near horizontal hovering position to a near vertical hovering position and peered at the water. In this raised position they would then lower to touch the tip of the attenuated outer tail feathers to the water, creating a ripple, then raise up and repeat the tail touch action, or alternatively return to a horizontal position whilst still watching the water surface intently. On some occasions the bird would drop and attack near where the tail had been touching, and other times the bird would rise and turn back without attacking.

The birds repeatedly carried out this action and it was not a single or casual occurrence, it was an oft repeated, apparently strategic, action.

Attenuated tail feathers can be seen touching the water, leaving ripples. This bird touched the water multiple times; others touched only once.

Another interpretation of this action could be that the bird was using its body to shade the water and so be better able to see below the surface to the prey. On this occasion this is not likely as the sun was often obscured by cloud and, with the sun in the east and the birds facing west, into the wind, the near horizontal position of the bird while hunting would have cast as much, if not more, shadow on the water in the area of the bird’s eyes than would a near vertical position, as can be seen in the photo.

Further observation is clearly needed on this matter but for whichever reason, attempting to block the sun or luring prey, the behaviour was intentional and repeated on numerous occasions by multiple members of the flock. Again, any feedback of similar sightings would be appreciated.

All text and photos © Jenny Spry

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