BIRD PELLETS—-EVIDENCE AS TO FOOD OF BIRDS, IIl5 
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. 0, 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 /, expansions containing lime 
crystals are shown ;'/, spores. 
BIRD PELLETS AND THEIR EVIDENCE AS 
TO THE FOOD OF BIRDS. 
BY PERCY THOMPSON, F.L.S. 
[ Read 25th November, 1922 ] 
T 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 feeces. This habit has not escaped the 
notice of some of our national poets. Thus, as Mr. J. E. Harting 
has pointed out', 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 pie 1871, p. 46. 
: Macbeth, mere lil. Sc. 
Aylmer’ s Field,’ 
