1872.] 931 [Trippe. 
ter, and scarcity in the former, of some birds whose range is toward 
the east. Hence it is probable that the high, treeless prairie forming 
the water-shed between the two great rivers, which extends north 
westwardly through Wayne, Lucas and Clarke Counties, forms a sort 
of natural barrier, which many species do not pass. ‘This conclusion 
is further borne‘out by the abundance of sylvan birds of all. descrip- 
tious in the woods in Mahaska County, the thickets and forests in 
May and June being fairly alive with Thrushes, Warblers, Vireos, 
Titmice, Nuthatches and scores of other birds, while in Decatur 
County, in the same season, the quiet and silence of the woods is very - 
apparent. There is also a perceptible difference in the flore of the 
the counties, one being considerably more eastern in its aspect than 
the other. | 
In comparing the fauna of the States bordering on the upper Mis- 
souri with that of Atlantic States on the same parallel, it should be 
borne in mind that the climate of the former is somewhat more se- 
vere than that of the latter; hotter in summer and colder in winter, 
although the mean annual temperature varies very little. Hence we 
should be led to expect more northern species in winter, and more 
southern species in summer, and this we find to be the case. The 
temperature of the spring and fall months, however, correspond very 
nearly with that on the coast, and the migrations of the birds occur 
very nearly at the same times, with the exception of a few species 
which arrive very early or depart very late. 
Of the one hundred and sixty-two species enumerated in the list, 
ninety-two were observed breeding, or in such numbers during the 
breeding season as to admit of no doubt of the fact. Of this number 
eighty-five were common, and seven rare. Eight or ten additional 
species undoubtedly breed here, though in such small numbers as to 
have eluded observation. Of the migratory species forty-five were 
abundant or common, and twenty-four scarce or rare. , 
On comparison with the avi-fauna of the same latitude on the At- 
lantic coast, we find but fifteen species breeding abundantly here, that 
do not also breed there, and of these eight are found a little further 
south in the east, and two formerly existed there, but have now become 
extinct, leaving but five species as characteristic of this region as dis- 
tinct from the Atlantic coast; an astonishingly small number, when 
we consider the immense difference in longitude. The similarity be- 
tween the migratory birds is equally striking, there not being over 
ten or twelve species peculiar to the western region. There is, how- 
