COMBINATION OF FIELD AND LABORATORY WORK. 15 
the month, but yearly averages are determined from the monthly 
averages; for unless the collections of stomachs were much more 
evenly distributed as to months than they are at present, an average 
based directly on the number of stomachs collected in the year would 
be misleading. 
COMBINATION OF FIELD AND LABORATORY WORK. 
Although the examination of a bird's stomach shows just what the 
bird has eaten, yet if this alone be depended upon information is still 
wanting as to what has been refused or what preferences exist, since 
the different elements of the food supply in the locality where the 
stomach was collected are not taken into account. If, however, this 
lacking information be obtained by means of field observation and 
osed in connection with stomach examination, the examiner will be 
enabled to make his analyses with the fullest degree of accuracy. 
In pursuance of this plan I have for several years systematically 
visited various farms in the neighborhood of Washington and col- 
lected data and material relating to the available food supply, to be 
used in connection with the examination of the stomach contents of 
birds collected in these localities. One example will serve to illus- 
trate this method. On May 13 and 18, 1808, I visited a farm of 75 
acres, mostly under cultivation, which was situated in a shallow 
depression surrounded by woodlands. It was traversed by three 
small bushy brooks, which ran among some cabbage plats, apple 
orchards, and cornfields (some newly sown and some with the last 
season's stalks). Between the cabbage rows was chickweed; in the 
apple orchard were the last year's stalks of lamb's-quarters with but 
few seeds, and in the old cornfield were great quantities of pigeon- 
grass and smart weed, though scarcely any seeds were left. Birds 
wen* numerous along the brooks and ran out into the fields among 
the dead weed-stalks, picking up food from the ground. The kinds 
of insects present were carefully noted and then the birds were 
watched with a glass for two hours, after which 17 sparrows, includ- 
ing field, chipping, white-throated, English, song, and Lincoln's spar- 
rows, were collected and their stomachs examined. Four had eaten 
seeds of lamb's-quarters and smartweed; 5, chickweed; and 6, crab- 
grass and pigeon-grass; 5 had taken cutworms (whose ravages had 
made it necessary to replant the cabbages twice): 6 had eaten small 
dung-beetles, and 10 had eaten weevils, specimens of which had been 
previously taken with a net on strawberry and clover. A dozen grass- 
hoppers had also been collected, but only 2 birds had eaten any. Use- 
ful predaceous ground-beetles (Carabida?) were very numerous and 
easily accessible, but the sparrows had eaten only one, while several 
other birds shot at the same place had eaten freely of them. 
Prom the knowledge gained by the study on this farm one could, 
with a fair degree of accuracy, predict what kind of food sparrows 
