^ CALIFORNIA SHRIKE 161 



hold territories limited by physical and associational barriers. Thus, 

 one pair was bounded to the south and northeast by steep hills, not 

 prohibitive to shrikes, but not so desirable as the flat meadow which 

 they occupied. To the east this j^air was limited by the holdings of 

 another pair of shrikes ; I witnessed several encounters between them. 

 To the west there was no change in association, no physical barrier, 

 and no other shrikes, yet this pair moved only a limited distance in a 

 westerly direction. Habit and lack of need for further foraging 

 ground apparently had fixed the western boundary. 



The defense of a territory is coincident partly with the foraging 

 habits of the bird, which keep it in more or less conspicuous, open 

 places. While a strike is hunting for food it can at the same time 

 see large parts of its territory. Detection of invaders is by sight, 

 less commonly by sound. When not engaged in active feeding, which 

 often is conducted from low^ perches, the shrike always tends to mount 

 to some high exposed position of observation. Here its ready visibility 

 aided by characteristic form and contrasting markings serves to adver- 

 tise at considerable distances its possession of the area. This advertise- 

 ment is aided by song and by the familiar series of 4 to 10 or 12 screeches 

 of progressively diminishing intensity. Loggerhead shrikes are in 

 the greatest degree silent during the nesting season, at which time 

 adult birds have reached the annual minimum in numbers and terri- 

 torial boundaries are well established. More constant, though less 

 ecstatic, songs and screeches are given late in summer and in autumn 

 when competition in the possession of territories is more severe. The 

 rhythmic summer song then seems certainly to be given for the pur- 

 pose of warning invaders. A bird in summer or fall perched quietly 

 on a wire or tree top suddenly, and without apparent reason, will break 

 out with its series of violent screeches. No other shrike appears, the 

 bird is not watching any particular prey, and it settles back again into 

 quiet waiting. The screech seems merely an expression of the bird's 

 presence, an indication of a potential aggi^essiveness to defend its 

 position. 



At Pinole I once witnessed a vigorous attack by the defender. 

 Members of the resident pair were sitting on fence posts about 10 

 yards apart, one bird, probably the male, singing occasionally. A 

 succession of sharp notes {IjBcelc) was heard from a third shrike, which 

 had appeared at the edge of the territory about GO yards distant. 

 This was immediately answered by similar notes from the defending 

 "male." The invader sang a few trills, then came closer, approaching 

 the "male" of the resident pair and sat on the adjacent fence post. 

 The "female" of the pair was on the opposite side of the defending 

 "male," which sat facing the invader. The two "males" remained 

 rigidly on guard, neither moving in the slightest. One of them, I could 

 not be sure which, gave a few song trills. After about five minutes 



