50 



NORTH AMERICAN FAUNA 69 



avoided during the second nesting when the female built her nest 

 there and started incubating. 



Defense of territories 



Territories are defended by singing, chasing, and combat. The 

 song signals ownership, and each male's primary advertising song 

 is usually different from his neighbor's. 



Paired males appear to be more aggressive than unpaired males 

 and usually initiate border encounters, which most often take 

 place along territory boundaries. A paired and an unpaired male 

 with adjacent territories at Macon, Ga., contended each time at 

 virtually the same point along the boundary. As these males 

 chased each other along the boundary, the paired female was 

 close by but remained 10 to 15 feet within her territory, chipping 

 excitedly. 



A territorial male with an incubating mate at Pendleton Ferry, 

 Ark., apparently had more time for hostile activity and thus was 

 involved more often than the Macon paired male, which I observed 

 during preincubation traveling with his mate. The Pendleton 

 Ferry male would fly from any point in his territory deliberately 

 to start a fight at the mutual boundary. He always began chipping 

 excitedly as he moved toward his neighbor's territory, and both 

 males chipped constantly during border clashes. In addition to 

 chasing, the birds fluttered about on the ground after making 

 contact and sometimes flew together a few feet up from the 

 ground, grasping each other's bill. 



Sometimes when a male invades a neighbor's territory and is 

 chased out, he may perform a display on his side of the boundary. 

 Such displays most often occur immediately after prolonged en- 

 counters. The wing and tail feathers are spread laterally (fig. 22), 

 and the tail is vibrated. The bird sidesteps back and forth along a 

 branch, frequently turning around, all the time chipping ex- 

 citedly. Ficken and Fi^ken (1962, p. 110) observed a similar dis- 

 play in the Redstart (Setophaga ruticilla). At the end of a chase 

 in which its adversary is evicted from the territory, a Swainson's 

 Warbler male may fly up to a perch and sing vigorously for 10 to 

 15 seconds. 



Following boundary encounters, males drift back into their 

 territories and usually sing unbroken courses of songs for several 

 minutes. Sometimes they start singing close to the boundary, in 

 which case songs are incomplete, consisting only of the first two 

 or three notes. Then as they move farther into their respective 

 territories, they sing more complete songs. 



