RATE OF INCREASE. 27 



extremes are concerned, for species increase in geometrical ratio. The 

 rate for some time after 1870 was comparatively slow, while during the 

 present decade it has progressed with astonishing rapidity, till in the 

 year 1886 the new territory invaded must have reached the enormous 

 number of 516,500 square miles, as may be seen from the following: 



Table showing approximately the extension in square miles of the English Sparrow, in 

 periods of five years each, from 1870 till 1885, and its extension during the year 1886. 



Squaro miles. 



From 1870 to 1875 it spread over 500 



From 1875 to 1880 it spread over 15,640 



From 1880 to 1885 it spread over 500,700 



la the year 1886 it spread over » 516,500 



This table of necessity is largely theoretical, though the ratio of increase must be 

 very nearly correct. Year by year much of the reproductive energy of the Sparrow 

 is expended in filling up the smaller towns and villages of the area which, so far as 

 tbe larger towns and cities are concerned, it covered some time previously. 



RATE OF INCREASE OF THE SPARROW. 



In asking for information as to the number of broods and young annu- 

 ally reared by the Sparrow, we hoped to receive many statements of 

 fact, but our expectations have been hardly realized, as most of the re- 

 plies seem to be mere guesses, not based on actual observation. 



The fact that more or less nest-building goes on during every month 

 of the year has led many people to suppose that the Sparrow breeds 

 continuously, but such is not the case, at least in temperate climates. 

 Enough material bearing on this point has been collected to show that 

 Sparrows rarely or never raise more than six broods in a year, and the 

 great majority probably do not raise more than four, at least in the lat- 

 itude of New York. 



In Washington the first young out of the nests may be seen in April, 

 but they are not abundant before the first week in May or after the 

 last week in August, though doubtless a few leave the nest in Septem- 

 ber, or still more rarely in October. 



It is possible that a few eggs may be laid even in December and 

 January, but it is extremely improbable that any young are reared 

 at that time. In the latter part of February, in some years, many 

 Sparrows begin laying, and occasionally a young brood may leave the 

 nest late in March, but such cases must be considered exceptional. 



Moreover, although nesting boxes may be steadily occupied by Spar- 

 rows with their young or eggs from the first of April to the first of Sep 

 tember, it does not follow that such boxes are tenanted all this time by 

 the same parent Sparrows, or that one brood follows another without 

 any interval. On an average, about four weeks elapse from the laying 

 of the first eggs to the time when the young brood leaves the nest. 

 The number of eggs in a set varies from four to seven, but is usually 

 either five or six, and these ordinarily would be deposited in one week. 

 Twelve or thirteen days are required to hatch them, and the young are 



