1914 ] 
Jackson: Land Vertebrates of Ridgeway Bog 
11 
study was begun in 1906, and was continued intermittently during 
August of that year, August 7-25, 1907, July in 1909, August 
10-20, 1911, and July 1-21, 1912. Most of the time during the 
first two summers was engaged in studying habits and habitat 
preference of mammals; during the summers of 1909, 1911, and 
1912 more attention was devoted to birds, reptiles, and batrach- 
ians. Specimens have been collected when necessary to deter- 
mine the presence and abundance of a species, and for identifi- 
cation, ^ but as far as possible the fauna has been undisturbed, 
one of the objects of the investigation being to determine the 
transformations and successions which naturally take place in 
the fauna within the area under observation. The location of 
the city near this bog has caused the extermination of some species 
which are found in bogs further removed from civilization, yet, 
on the whole, the area has a fauna very typical of northern bogs. 
The present paper considers primarily the horizontal distribution 
and the succession of the breeding terrestrial vertebrates in this 
bog, and the probable source of their ingressioii'^ into the region. 
Ecological associations are, however, most clearly enunciated by 
the plant associations which appear to the eye more diagnostic 
than animal associations; a few of the more characteristic seed 
plants are therefore included in the present study. No attempt 
is here made to discuss vertical distribution, that is, ecological 
stratification,^ physical factors and their effect upon the animals, 
causes of succession and of habitat preference, habits and behavior 
2 All the vertebrates have been identified personally by the author with the exception of 
Ra?ia septentrionalis which kindly has been determined for me by Dr. L. Stejneger. 
2 I use the term ingression, or ingressive dispersal, for the encroachment or advance of a species, 
a group of species, or a mores into a new geographic range, in contradistinction to invasion, the 
encroachment or advance of a species, a group of species, or a mores into a new habitat. Ingres- 
sion is to geographic dispersal what invasion is to ecological succession. Egression is the converse 
of ingression; that is, it is the withdrawal of a species, a group of species, or a mores from a region, 
either by extermination or migration. 
* Warming has classified the different stories or strata of plants into (1) the ground-stratum, 
immediately above the soil, mainly mosses, lichens and algae; (2) the field-stratum, formed by 
grass and herbs, as well as by small shrubs of approximately the same stature; (3) the shrub- 
stratum, formed by taller shrubs; and (4) the tree-stratum (Warming, 1909, p. 138). Shelford has 
applied a similar classification to animals: “In any locality we note that there are several levels 
which may be occupied by animals. Some animals live below the surface of the ground and 
constitute the Subterranean stratum. Others live at the surface of the ground and constitute 
the Ground stratum. Animals inhabiting the herbaceous vegetation, and low shrubs, etc., make 
up the Field stratum. Those living on the shrubs and young trees make up the Shrub stratum, 
and those on the trees, the Tree stratum.'' (Shelford, 1912a, p. 65.) 
