Russ Kinne; Comstock 



Hooded warblers frequent the understory of woodlands. A 

 male in Point Pelee, Ontario, near the extreme northern edge 

 of the hooded warbler's range, peers at sprigs of poison ivy, 

 right. Below: A pair share in the care and feeding of their 

 young, which are within two days of fledging. 



George K. Peck 



near the "correct" boundary of a subject's 

 territory. As expected from our previous 

 experiments, the subject's response was 

 weak, the normal result for a dear enemy. 

 Then this same neighbor's songs were 

 broadcast from two locations deep inside 

 the subject's territory (we stopped the 

 playbacks as soon as the subject arrived 

 nearby, so it would not learn that the 

 neighbor was not actually present). Fol- 

 lowing this simulated trespass, we once 

 again presented the same neighbor's songs 

 near the correct boundary. The result was 

 clear: a subject responded much more 

 strongly to a neighbor's songs following 

 an apparent trespass. When we staged 

 trespasses with a stranger's songs, retaUa- 

 tion toward a neighbor did not occur. Re- 

 taliation was therefore restricted to the 

 trespassing individual, just as predicted 

 for rivals playing tit-for-tat. 



Over the years, we have come to appre- 

 ciate the intricate lives led by hooded war- 

 blers. They know their neighbors and 

 work out mutually advantageous relation- 

 ships with them. The trust required for 

 these relationships, however, is not 

 "naive." While not demanding "an eye for 

 an eye" following trespass, they do be- 

 come antagonistic toward wayward neigh- 

 bors. We have also noticed that in the days 

 following a simulated trespass, our sub- 



jects' behavior returned to normal. Given 

 a httle time, warblers appear to "forgive" 

 their trespassers. 



What we have found could well apply 

 to other migratory songbirds that defend 

 territories during the breeding season. If 

 so, our studies suggest another way in 

 which habitat destruction can have devas- 

 tating effects on populations of migrating 

 birds. For a surviving male hooded war- 

 bler headed north for the summer, not all 

 habitat, not even habitat suitable in general 

 for the species, is optimal. Each individual 

 seeks out the one specific place where it 

 has an advantage — its territory from the 

 previous year, where it will meet some of 

 its old neighbors. If a particular stretch of 

 forest has disappeared, oiu^ individual mi- 

 grant must start over. 



April is a time of blossoming opportuni- 

 ties. For the hooded warblers arriving on 

 each southerly wind, it is also a time of es- 

 tablishing and renewing relationships, in- 

 cluding those with their neighbors. By 

 mid-May, most males in the Mason Farm 

 Biological Reserve will have mates incu- 

 bating three or four eggs in nests cradled 

 on stems of arrowwood. Those nests that 

 escape predators and cowbirds (about half 

 of the total built) will produce a new gen- 

 eration of hooded warblers to carry on the 

 tradition of dear enemies. D 





40 Natural History 5/94 



