100
THE ESSEX NATURALIST.
estuary, and these birds are so tame that I have been able to
see the thickening of the leg-joint indicative of immaturity. The
usual call of these youngsters is a tri-syllabic "too, too, too,"
very loud and emphatic, often heard at night during the autumn
migration.
For a week or more in January 1918 a single Curlew haunted
the Sewage Farm at Theydon Bois, and I have come across the
bird on rare occasions in other parts of inland Essex; but,
strangely enough, I seldom hear this species on migration over
Theydon. The rippling whistle of the Whimbrel is not unusual
in May, and of course I have seen this passage-bird in fair numbers
on the fields bordering the coast.
On the 4th May 1912 a couple of handsome Black Terns
were hawking for (apparently) emerging caddis-flies over the
lake at Navestock. The white patch below the tail was very
striking against the dark plumage.
Gulls, I think, are, considering the proximity to the sea
and to the Thames at London, strangely rare near Theydon
Bois, and I do not often see them. The abundance of the Greater
Black Back along the Thames Estuary below Grays struck me
as noteworthy in winter.
The Little Grebe nests in some numbers at Birch Hall,
where I have sometimes been able to watch the swift movements
(a second's work) by which the bird draws a concealing layer
of rotten weeds over its eggs before leaving the nest on alarm.
The uninformed observer would most certainly fail to recognise
the structure then as a bird's nest, and the bird itself is an
accomplished hideling. A Little Grebe picked up unhurt in the
road outside spent a few hours in my bathroom before I re-
leased it. Very often it used alternate strokes of the feet in
paddling around the bath, and on alarm its sudden change in
draught was remarkable, the body dropping in the water as
though it had been pulled down.11 A piece of board was placed
in the bath for a perch; but when we entered the room the
Grebe always dived under the wood, holding the top of the head
to the nostrils above the surface of the water, and staying in this
position as long as we remained in the room.
11 Zoologist, 1910, p, 201