1194 Life-histories of Northern Animals 



where fly the great, fat luna moths and the cecropias, with 

 others half as big as itself and worthy of its powers. In one 

 other respect it has a proper sphere — it appears later at night 

 (or earlier in the dawn) than any others of the tribe on our list. 



In the Silvery-bat chapter we have noticed the nightly 

 order of appearance that is, in a general way, observed by the 

 Bats, and the present handsome creature, as befits its impor- 

 tance, is the last to appear. 



Dr. Merriam's observations on this point, made in Lewis 

 County, N. Y., are very complete, as well as the only ones 

 available. 



"The hour," says he,^ "at which Bats leave their retreats 

 to begin their nocturnal excursion is governed, first, by the 

 latitude, longitude, and altitude of the locality, and the time of 

 the year; and, second, by the character of the sky (whether 

 clear or overcast) and the exposure — those living along the 

 southern and eastern borders of woodlands and in dark ravines 

 appearing earlier than those whose hiding places face the setting 

 sun. In other words, the time at which Bats appear depends 

 solely upon the degree of darkness.' 



"Hence it follows that their nightly exodus, in a given 

 locality, does not take place in a fixed period after the disap- 

 pearance of the sun, for, during the first part of October, in 

 this latitude, the darkness is as great half an hour after sunset 

 as it is an hour after, three months earlier. Therefore, in esti- 

 mating the exact hour at which Bats are to be expected at any 

 stated date, it is necessary not only to consider the time the sun 

 sets, but also to take into account the duration of the twilight. 

 Moreover, in the same locality, the several species do not com- 

 mence to fly at the same hour, for each seems to await a par- 

 ticular and different degree of darkness. The Hoary-bat is one 

 of the last to appear, and for this reason its capture is the most 

 difficult. In Lewis County, during the latter part of June, it 

 does not start out (excepting in deep forests and dark valleys) 

 till about 8.45 P. M., or a full hour after sunset, while in the 

 early part of October I have killed it at 6 p. m., or just half an 



' Mam. Adir., 1884, pp. 180-1. ' Italics mine. — E. T. S. 



