554 EXPERIMENT STATION RECORD. 



In March, 1905, 200 steel n-aps were set, uncovered and unbaited, each trap 

 being visited at least twice daily. Poison was also used to a moderate extent. 

 A total of 925 squirrels was killed, at an estimated cost of $92. In 190G the 

 same methods and moi-e traps were employed and I.CjG squirrels killed, at a 

 cost of $112. In 1907, 170 acres were added to the college farm, making a 

 total of over 400 acres, 1,875 squirrels being killed, at a cost of $170. The 

 work was continued through to 1910, 1,704 squirrels being killed in 1908, 

 1,280 in 1909, and 460 in 1910, the cost being $172, $140, and $28, respectively. 



The average cost of killing squirrels for the entire period was a little less 

 than 9 cts. each, exclusive of the cost of the traps. It was found that, aside 

 from the necessary protection to the experimental plats and crops, the squirrels 

 were destroyed at a cost much below the damage which they would have caused 

 if allowed to remain. As an argument in favor of trapping rather than 

 poisoning, the author cites a case in which GO horned larks were killed on a 

 5-acre field by poison intended for squirrels. 



Rats and fleas in their relation to bubonic plague, A. H. Jennings {Proc. 

 Canal Zone Med. Assoc., 1910, Apr.-Sept., pp. 119-133). — The author here reports 

 upon investigations made of the species of i-ats and fleas and their distribution 

 in the city of Panama and the Canal Zone. 



The rats trapped in the routine work of the Panama Department of Health 

 were delivered to the Board of Health Laboratory, where they were chloro- 

 formed and searched for fleas. In all, 2,292 rats of four speciss were examined. 

 They were brown rats, 1,513; black, 653; roof, 77; mouse, 49. From these 

 rats 2,784 fleas were taken. Single rats often greatly exceeded the average 

 of their species, the highest number for one rat being 39 fleas. But two species 

 of fleas were taken from the rats examined, the Indian rat flea, Xenopsylla 

 cheopis, and the cat flea, Ctenocephalus felis, the former forming 97.9 per 

 cent of the entire number. Three other species of fleas, namely, the European 

 rat flea, Ceratophylhis fasciatus; the European mouse flea, Ctenopsylla musculi; 

 and the human flea, Pulex irritant, have, however, been taken from or are 

 thought to occur in the Canal Zone. 



A tabulated summary is given of the relationship of rats and fleas taken 

 from districts in the city of Panama. 



The migratory movements of birds in relation to the weather, W. W. Cooke 

 {U. 8. Dept. Agr. Yearbook 1910, pp. 379-390, map 1). — The data here presented 

 are based on 400,000 records. 



It is shown that "weather conditions are not the cause of the migration 

 of birds, but that the weather, by influencing the food supply, is the chief 

 factor which determines the average date of arrival at the breeding grounds. 

 Migration is undertaken in response to physiological changes in birds, and 

 the date of starting in the case of most species bears no relation whatever to 

 the local weather conditions in the winter home. The weather encountered 

 en route influences migration in a subordinate way, retarding or accelerating 

 the birds' advance by only a few days and having a slight relation to the date 

 of arrival at the nesting site. Local weather conditions on the day of arrival 

 at any given locality are minor factors in determining the appearance of a 

 species at that place and time. The major factors in the problem are the 

 weather conditions far to the southward, where the night's flight began, and the 

 relation which that place and time bear to the average position of the bird 

 under normal weather conditions. . . . 



"Another conclusion equally apparent is that neither the time of migration, 

 the route, nor the speed of one species can be deduced from records of other 

 species, even though closely related; in other words, each species and even 

 each group of individuals of a species is a law unto itself," 



