NATURAL ENEMIES: BIRDS. ao 
published data concerning certain species of birds, that bureau has 
an immense collection of unpublished records and these have been 
very kindly put at my disposal for the purpose of this study. Practi- 
cally all of the data here presented on this point were derived from 
this material. While these records do not, in most cases, give the 
particular kind of leafhopper which is fed upon by certain species of 
birds, it should represent, of course, the kinds of leafhoppers which 
were abundant at the time and place indicated. The birds, of course, 
make no discrimination between species, except as they might appear 
in numbers or prove an easier prey. 
EVIDENCE AS TO THE RELATION OF BIRDS TO LEAFHOPPERS. 
While at first thought we might consider birds as a most important 
element in control of these insects, a closer study reveals many reasons 
why they must depend upon them but little as a food supply. Even 
with this more conservative view in mind, however, the actual con- 
dition as represented by the records of the Biological Survey are 
rather disappointing since they show that for practically all of our 
common birds the leafhoppers constitute so small a portion of their 
food supply that birds very properly may be considered as almost 
negligible in any consideration of the natural agencies of control. 
It is, however, important, both as a matter of record and for the 
benefit of future workers, that the actual condition as indicated by 
these records should be made available, and I have endeavored to 
sum up, as briefly as possible, the results of an analysis of the figures 
obtained, and the table of records is appended. 
According to the records consulted by me and later revised 
by the Biological Survey, there are 119 different species of birds 
among those examined by that bureau whose stomachs contained 
jassid remains in various proportions, from a trace to 80 per cent. 
But, putting all the stomachs together, we have only 770 which 
contained jassid material out of a total of some 47,000 stomachs 
examined, or less than one out of fifty. 
Even for the species of birds showing jassids in their food, we have 
only 770 out of about 28,000 (about 1 in 40) stomachs which ineluded 
jassid remains and for a large majority of these stomachs examined 
the jassid contents were but from 1 to 10 per cent, so that on a most 
liberal estimate we can claim about the thousandth part of the food 
of birds as being made up of leafhoppers. 
However, this general average may not represent the actual con- 
dition of effectiveness, for some of our most common birds abound 
in pastures and meadows where leafhoppers occur, and a critical 
examination for such species is desirable. 
In the first place we may eliminate practically all the waterfowl— 
loons, divers, gulls, terns, pelicans, ducks, geese, cranes, bitterns, 
