BIRD PELLETS—EVIDENCE AS TO FOOD OF BIRDS. 115
sum Fr. it may be distinguished by the absence of columella and
the more spinose spores.
DESCRIPTION OF THE PLATE.
a, Didymium trachysporum n. sp. on fragment of elm leaf
from Weybridge, Surrey. b, a smooth sporangium and a plasmo-
diocarp with wrinkled wall (enlarged from a); c, smooth sporangia
on straw from Leytonstone, Essex; d, e, f, g, various forms of
capillitium and lime crystals; in f, expansions containing lime
crystals are shown; h, spores.
BIRD PELLETS AND THEIR EVIDENCE AS
TO THE FOOD OF BIRDS.
BY PERCY THOMPSON, F.L.S.
[Read 25th November, 1922]
IT is common knowledge among ornithologists that certain
birds have the constant habit of casting up, by way of
the mouth, the indigestible portions of their food in the form of
more or less agglutinated ovoid masses known as "pellets"
or "castings." These "pellets," containing as they do only
the harder portions of the food which have resisted the solvent
action of the digestive juices of the bird, still present their con-
tents in recognisable form, and so afford valuable evidence as
to the nature of the bird's ordinary food, evidence which would
be entirely lost in the faeces. This habit has not escaped the
notice of some of our national poets. Thus, as Mr. J. E. Harting
has pointed out1, Shakespeare, ever quick to use a nature simile,
makes Macbeth say at the apparition of Banquo's Ghost:—
If charnel-houses and, our graves must send
Those that we bury back, our monuments
Shall be the maws of kites.2
showing that the poet was acquainted with the habit in the case
of the Kite, in his day a common scavenger of London streets.
Tennyson, another keen observer of natural things, in a
charming passage explicitly refers to this habit in the case of
raptorial birds. Picturing the decay and desolation of a great
estate whose heiress meets with an untimely death, he says:
And where the two contrived their daughter's good.
Lies the hawk's cast.3
1 The Ornithology of Shakespeare, 1871, p. 46.
2 Macbeth, Act. III. Sc. 4.
3 "Aylmer's Field."