ARCTIC TOWHEE 581 



PIPILO ERYTHROPHTHALMUS ARCTIGUS (Swainson) 



Arctic Towhee 

 Contributed by Oliver L. Austin, Jr. 



Habits 



This and the following 11 subspecies, plus some 8 more races resident 

 extralimitally in Mexico and Guatemala, form a complex commonly 

 called the spotted-backed towhees. All show varying amounts of 

 white streaks or spots on the scapulars and wing coverts, which occur 

 very rarely in the four eastern races treated in the preceding account. 

 In addition, females of these western races have the black of the male 

 replaced by dark gray instead of the reddish brown of eastern females. 

 Until recently they were regarded as specifically distinct from the 

 eastern forms and grouped together in the species Pipilo maculatus. 

 In suggesting the conspecificity of the maculatus and erythrophthalmus 

 groups, Charles G. Sibley (1950) notes that "many specimens of other- 

 wise typical P. e. erythrophthalmus have varying amounts of white 

 spotting on the same feathers which are normally spotted in the races 

 inhabiting Mexico and the western United States" and adds: 



1. In all plumage characters other than the dorsal spotting, the two are Identical 

 except for normal geographic variation. 



2. Eggs and nests are no more different than is to be expected between sub- 

 species. 



3. Ecological requirements vary more within the spotted races than between 

 the spotted and the eastern ones. 



In a later paper, Sibley (1959) suggests: 



The geographical distribution of the dorsal color pattern suggests that it has 

 adaptive significance in some way correlated with climate. The races which are 

 spotted dorsally (maculatus group) tend to live in areas which are more arid than 

 those occupied by the unspotted erythropthalmus group. The vegetation occupied 

 by the spotted races is usually a "chaparral" formation of woody shrubs without 

 an arboreal cover. The unspotted races tend to occupy the understory shrubbery 

 of eastern deciduous woodlands, a formation of more humid climates. Common 

 observation indicates that the amount of sunlight reaching the ground and pro- 

 ducing a sun-dappled pattern will be greater in a chaparral habitat than in a wood- 

 land habitat where the canopy will intercept more of the light. Hence we suggest 

 that the dorsal spotting is a cryptic pattern induced by selection through predation 

 and correlated indirectly with climate through the effects described. 



In appearance arcticus is closest to P. e. montanus, from which it 

 differs chiefly in having heavier white dorsal spotting and a more 

 olivaceous back. In his original description of the form Swainson 

 (1831) states he observed it "only on the plains of the Saskatchewan," 

 where it frequented shady and moist clumps of wood, being generally 

 seen on the ground. He says "It feeds on grubs, and is a solitary and 

 retired, but not a distrustful bird." P. A. Taverner (1926) remarks: 



