ful, Oryzaephilns is eliminated. But when the flour 

 medium contains pieces of glass tubing of such bore 

 as will exclude Tribolium but let the larvae of Ory- 

 zaephilns enter and pupate, both species survive 

 (Crombie 1946). 



Most vertebrates and some invertebrates, espe- 

 cially insects and spiders, build nests, usually of plant 

 material. The type of nest it builds is grossly char- 

 acteristic of a species and dependent on inherited be- 

 havior patterns, yet individual nests are uniquely 

 modified to fit into particular situations. Nests pro- 

 tect eggs and young against weather, and are usually 

 well concealed from enemies. 



Bird species are commonly found at different 

 heights or in particular strata of the vegetation asso- 

 ciated with the characteristic location of their nests 

 (Beecher 1942), where they seek refuge from ene- 

 mies (Dunlavy 1935), where they do their feeding 

 (Hartley 1953), or the location of their song-posts 

 (Kendeigh 1947). Birds nesting in the tree-tops 

 often feed outside the forest (Colquhoun and Mor- 

 ley 1943). Bird feet are as variously adapted to 

 foraging in different strata or in different habitats as 

 bills are variously adapted to procuring different 

 kinds of food. It is often obvious, from the arrange- 

 ment of toes, length of the legs, and other character- 

 istics, whether a bird scratches the ground for its 

 food, gets its food in the air, wades in marsh, is a 

 swimmer and diver, a percher, or a tree-trunk 

 climber. However, the minor adaptations of legs, bill, 

 and wings in closely related species that enable them 

 to occupy different niches within the same general 

 type of vegetation are more difficult to detect ( Dilger 

 1956). Segregation to a niche may involve, in addi- 

 tion to obvious external characters, many adaptations 

 throughout the body in skeleton, musculature, and 

 other organs (Burt 1930, Richardson 1942). Many 

 types of animals other than birds, for instance mos- 

 quitoes, are segregated by strata to where they most 

 commonly occur (.Snow 1955). 



Warblers are numerous in the evergreen-decidu- 

 ous forest ecotone of eastern North America because 

 they nest and feed in so many diverse niches (Ken- 

 deigh 1945) : 



Blackburnian warbler — top level of evergreen 



trees 

 Black-throated green warbler — middle level of 



evergreen trees 

 Magnolia warbler — low level of evergreen 



trees 

 Redstart — secondary deciduous growth 

 Black and white warbler — tree trunks 

 Black-throated blue warbler — shaded shrubs 

 Chestnut-sided warbler — sunlit shrubs 

 Canada warbler — wet shaded ground 

 Yellowthroat — wet sunlit ground 



Ovenbird — dry shaded ground 

 Nashville warbler — dry sunlit ground 

 Louisiana waterthrush — stream margin 

 Northern waterthrush — bog forest 



Mammalian adaptations to different strata have al- 

 ready been discussed. When given a choice between 

 a grassy habitat and a tree-trunk habitat, the short- 

 tailed forms of Peromyscus mice selected the grassy 

 habitat; the long-tailed forms, the tree-trunk habitat 

 (Harris 1952). It has been demonstrated that the 

 long tails of some species and subspecies give them a 

 greater proficiency in climbing than their shorter- 

 tailed relatives exhibit (Horner 1954). In the arid 

 country of southern California the giant kangaroo 

 rat is predominant in flat country covered with brush ; 

 on brushy slopes and rolling hilltops the Fresno kan- .. 



garoo rat replaces the giant kangaroo rat ; the Heer- 

 mann's kangaroo rat is forced to live on the open 

 plains since it cannot compete successfully with the 

 other two species on brush-covered land (Haw- 

 becker 1951). 



Considerable evidence was presented in Chapters 

 7, 8, and 9 to show how animal distribution corre- 

 lates locally with types of vegetation, and more will 

 be presented in Section IV with respect to geographic 

 distribution. Except for a few herbivorous and para- 

 sitic species, animals do not respond to the taxonomic 

 composition of vegetation when they seek cover or 

 food, but rather to life-form of plants : or they re- 

 spond to the micro-climatic conditions established by 

 the vegetation. 



In northern Europe, the kinglet Rcgulus rcgiilus 

 occurs with the chickadee Panis atricapillus in spruce 

 and pine forests, but is mostly absent from the birch 

 forests which the chickadee frequents. The kinglet 

 is unable to feed extensively at tips of the pendulous 

 birch twigs because, unlike the chickadee, it is less 

 able to hold itself in an inverted position, because of 

 poor development of certain muscles in the leg 

 (Palmgren 1932). 



The ovenbird is absent from coniferous forests 

 unless a few deciduous trees are also present, since 

 the bird requires broad leaves for construction of its 

 oven-shaped ground nest. The red-eyed vireo feeds 

 on insects taken from the leaves and the smaller stiff 

 twigs of deciduous trees. It is mostly absent from 

 coniferous forests where the needle-shaped leaves are 

 attached on all sides of flexible twigs and the bird 

 finds difficulty in obtaining a footing (Kendeigh 

 1 945 ) . When birds of different species were given a 

 choice between the branches of coniferous trees and 

 those of deciduous trees, there was evident a direct 

 correlation between length of foot-span, i.e., the dis- 

 tance from the tip of the middle front toe to the tip of 

 the hind toe, and the frequency of perching on the 

 evergreen branches. Birds with small foot-spans 



248 Ecological processes and dynamics 



