BIRD ENEMIES INTRODUCED BY MAN 141 



Numerous correspondents had known individual 

 cats to kill from two to eight birds in a day, though 

 the average was much smaller. In several cases cats 

 were known to kill almost or more than fifty birds 

 in a year. 



The reports showed that 



226 cats killed 624 birds in one day, an average per day of 2.7. 



32 cats killed 239 birds in one week, an average per week of 7.9. 

 15 cats killed 307. birds in one month, an average per month of 20.4. 

 47 cats killed 534 birds in one year, an average per year of 11.3. 



The average for the year is small because few 

 persons kept careful account of the birds killed 

 during a whole year, while others, whose cats had 

 been "taught not to kill birds," reported that their 

 cats had killed only one, two, or three birds in a year. 



If we assume that these cats continued to kill 

 birds at the same rate for one month and average 

 them all, taking into account the number of cats 

 in each group, the average for a month is 62. If we 

 give the four groups equal consideration, regard- 

 less of the number in each group, the average num- 

 ber killed is 33. The average of the third group 

 alone, comprising 15 cats, is 20.4. And if finally 

 we average these three averages, the result is 38. 

 In order to make a conservative estimate, we will 

 take the lowest of the four averages, 20.4 as the 

 average number of birds killed in a month by one 

 cat. It is fair to assume that a cat would continue 

 to kill birds at this rate during at least one month 



