Sunday, 17 March 2013

Comings and goings

Despite the reluctance of winter to give way to spring, comings and goings have been evident in the last few days.  Today at Hall Marsh, where some excellent management has been undertaken by the Lee Valley Park, a Little Ringed Plover was back on territory, a Sand Martin headed north and a Chiffchaff sang from nearby bushes.

A few days earlier I had waited in vain at Amwell for a Great White Egret to return to the roost, but luckily witnessed a far more interesting event.  At dusk a Bittern drifted headed across the lake and dropped into its usual reedbed roost site. Nothing unusual there.   However, 15 minutes later, in the gathering gloom it rose out of the reedbed to begin circling up into the sky giving the little known ‘gull call’.  Within a minute or two a second bird had risen out of the reeds to join it, both dark shapes now just visible circling over the lake.  As they rose and drifted northwards, a third calling bird appeared from the south to circle the lake.  This bird disappeared high into the gloom back southwards with its far carrying call audible long after the gloom had swallowed up it’s shape. 
The ‘gull call’ can be given by both male and female Bitterns and has mainly been associated with pre-migration behaviour when birds circle up into the sky at dusk.  This behaviour is well known on the continent, where groups of up to 20 birds are noted at key wintering or passage sites.  However, the ‘gull call’ may also be heard in aerial chases over breeding sites in early spring. 

Although many of our wintering Bitterns are assumed to come from the continent, there is little firm evidence of this.  However, satellite tagging birds in the Netherlands has produced some interesting results.  Check out Anneke on this page.    Anneke was ringed in the Netherlands in 2011.  In October she arrived in the UK over Hull, toured Wales and then settled at Slapton Ley in Devon from late November to the end of February. On February 26, she flew back to the Netherlands with a stopover in East London after a flight of 900 m above the city.  Then she returned to her natal site, crossing the North Sea at over 60 miles per hour.

So our Lee Valley birds may be heading back to distant breeding areas but there is plenty of Bittern breeding activity in the UK already this spring, with a remarkable 35 booming birds in Somerset, good numbers in the north of England and some new sites occupied. With Great White Egrets also getting jiggy on at least two sites, this spring will be interesting.

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