558 



THE QUARTERLY REVIEW OF BIOLOGY 



breeding area within the confines of which 

 they tolerate no others of their own 

 species. The size of the territory in most 

 cases seems to depend on the abundance 

 and availability of food for the young. 

 As a rule (in by far the greatest number of 

 instances) the males establish the terri- 

 tories and wait there for the arrival of the 

 females. The females then choose the 

 exact site of the nest within the territories 

 of their respective mates. The establish- 

 ment of the territory is primarily the 

 business of the male, and his main task 

 during the early part of the breeding 

 season seems to be the defense and main- 

 tainance of the territory. The territory 

 seems more fundamental than the nest in 

 the complex of instincts of the male. 



It follows that the sexual relations of 

 the birds (i.e. monogamy vs. promiscuity, 

 etc.) depend largely on their territorial 

 relations, and inasmuch as these two are 

 intimately bound up with the mode of 

 reproduction, we may profitably examine 

 the territorial situation in the cowbirds. 



In the Bay-winged Cowbird the problem 

 is somewhat simpler than in the others, 

 as each pair has its nest and is thereby 

 tied down to a definite area. However, 

 instead of the usual procedure, we find 

 the reverse is followed. The wintering 

 flocks break up into pairs in the spring, 

 and the pairs of birds go about looking, 

 not for territories, but for nests. They 

 will fight with the builders, if need be, to 

 gain possession of the nest, or else will 

 quietly occupy an uncontested one. Then 

 the territory is extended radially around 

 the nest, instead of the nest-site being 

 chosen within the territory as in normal 

 birds. 



This altered conception of the breeding 

 territory manifests itself in the defense of 

 that territory. Instead of being the basic 

 thing, the area becomes secondary to the 

 nest and its defense is correspondingly 



weakened or lessened. This weakening of 

 the defense opens an easy path to a dis- 

 torted type of sexual relations, such as 

 promiscuity or polyandry. 



The territorial situation in the case of 

 the next species, the Screaming Cowbird, is 

 of interest in that it presents a rather 

 unusual state of affairs, although super- 

 ficially it seems quite ordinary. This 

 species, as already noted, pairs off early 

 in the season but does not begin to breed 

 until nearly midsummer (January and 

 February). Nevertheless, quite early in 

 the spring it establishes its territories, 

 often as early as the first week in October. 

 Sometimes the period elapsing between 

 the time of territorial establishment and 

 the actual inception of egg-laying amounts 

 to two or even nearly three months. Yet 

 during all this time each pair maintains 

 its particular sphere of influence. Pairs 

 from adjacent territories do not join or 

 mix promiscuously although they do 

 sometimes form temporary groups of four 

 to six birds in neutral feeding areas. 

 Having no nests to care for or young to 

 provide with food, why should these 

 birds establish territories and stay in them 

 day after day, sometimes for nearly a 

 quarter of a year, without making any use 

 of them? One would hardly expect a 

 nonparasitic species endowed with strong, 

 fully developed parental instincts to limit 

 its individual liberty of action for so long 

 a time merely in anticipation of, and 

 preparation for, its reproductive activities. 

 The Goldfinch of North America (Astraga- 

 Unus tristis) breeds at the same relative 

 season (reversed) as the Screaming Cow- 

 bird, but the flocks of the former do not 

 break up for pairing and breeding purposes 

 until about a month before egg-laying 

 commences. Furthermore, not only do 

 they have to establish territories and 

 procure mates in this month but also to 

 build nests, which the Screaming Cowbird 



