Preface. 
164 
visited Illinois territory. A few species ( e . y. Picarustica hud- 
sonica and Lagopus albus) are given upon the authority of Mr. 
Robert Kennicott, but have not been noted by any subsequent 
observer. They may not now occur in Illinois, but this does 
not, however, affect the validity of Mr Kennicott’ s record, which 
cannot be passed over on the strength of purely negative 
evidence. 
In the catalogue of 1874 I gave a list of 48 species “to be 
looked for” in Illinois, and which it was stated would “no doubt 
be yet found to occur within the limits of the state.” Of these 
no less than 15 have already been taken or observed, besides 
four ( D ichro m ana-ssa rufa , Ajaja rosea , Pelecanus fuscus and 
Stercorarius parasiticus') whose occurence had not been antici- 
pated. We may therefore look with confidence tathe capture 
of the remaining species of the list, when the extreme southern 
and northwestern borders of the state have been more thoroughly 
explored. 
As may be seen from an examination of the following cata- 
logue, the avian-fauna of Illinois is exceedingly rich and varied, 
probably no inland state or territory, not traversed by lofty 
mountain ranges, being equal to Illinois in this respect. This 
great richness and diversity of bird-life results primarily from 
two causes, — the central position of the state geographically, 
and its great extent from north to south. The variety of surface 
which the state presents in different sections, notwithstanding 
the prevalence of large prairies, is also an important factor, 
no state, perhaps, east of the Pacific slope presenting greater 
contrasts of this kind. Stretching through nearly six degrees 
of latitude, the climates of the northern and southern portions 
are very diverse, the advent of spring, as determined by the 
first flowering and leafing of identical plants, averaging fully six 
weeks earlier near the Ohio river than in the vicinity of Chicago.* 
§The difference in climate between Cairo and Chicago, as determined by the U. S. 
Signal Bureau, is as follows: 
An. mean. 
Av. of hottest month. 
Av. of coldest month. 
An. range. 
Latitude. 
Cairo 
57.3 
80.2 (August.) 
31.3 (January.) 
37.00 
Chicago 
46.7 
72.8 (July.)' 
20 (December.) 
41° 52’ 
