Friday, 18 August 2017

Grebe is behind other waterfowl in rearing its young

THE river is teeming with goslings, ducklings, cygnets and cootlings at all their usual haunts — on the Fawley bank by Temple Island, fighting to be fed by the prom and among the reeds at Remenham Club.

However, the grebes do not seem to be nesting yet.

A coot is sitting on eggs on a floating nest perched on a fallen branch under the bridge at Marsh Lock, while above the lock the grebe is still calling his mate — “kraah-erh, kraah-erh” — neck outstretched, sitting low on the water.

They are able to compact their feathers, expelling the air from them, and empty their air sacs to float low or sink beneath the surface.

While mammals have a diaphragm to stimulate the involuntary muscles of the lungs, birds have four air sacs surrounding the lungs which balance the intake of breath.

The grebe can deflate them, lower its buoyancy and glide silently down, whereas coots and cormorants have to jump up and dive down head first and geese and swans can only up-end. Their 20,000 feathers are impervious to moisture and they remain on the water all their lives, using floating nests like the coot, being hardly able to walk on land as their legs are set well back to give thrust for swimming.

The incubation of the eggs takes up to 28 days, with the parents changing places every three hours, then both will also feed and carry the young on their backs, as do swans.

Since persecution ended at the beginning of the last century, their numbers have gradually increased until every gravel pit, reservoir and river now has its grebe territories and there is competition for suitable nest sites.

Meanwhile, the garden is infested with ugly black bugs with orange waistcoats which are actually the larvae of the sevenspot ladybird, coccinella septempunctata.

They will pupate as orange and black dots on brown plant stems before emerging to what should be a strong ladybird year — much needed to eat the aphids which have multiplied in the dry weather.

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