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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