COMBINATION OF FIELD AND LABOEATORY 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, j^et 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 

 used 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, 1898, 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 smartweed, though scarcely any seeds were left. Birds 

 were 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 (Carabidse) 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. 



From the knowledge gained by the study on this farm one could, 

 with a fair degree of accuracy, predict what kind of food sparrows 



