Article Contentsp. [45]p. 46p. 47p. 48p. 49p. 50Issue Table of ContentsBehavioral Ecology and Sociobiology, Vol. 33, No. 1 (1993), pp. A1-A2+1-66+A3-A5Front Matter [pp. A1-A2]Echolocation in Two Very Small Bats from Thailand: Craseonycteris thonglongyai and Myotis siligorensis [pp. 1-12]Parasite Faunas, Testosterone and Secondary Sexual Traits in Male Red-Winged Blackbirds [pp. 13-23]Polyandry and Its Effect on Female Reproduction in the Green-Veined White Butterfly (Pieris napi L.) [pp. 25-33]Thermal Constraints on Prey-Capture Behavior of a Burrowing Spider in a Hot Environment [pp. 35-43]Tit for Tat among Neighboring Hooded Warblers [pp. 45-50]The Stop Signal of Honey Bees: Reconsidering Its Message [pp. 51-56]Testing Hotspot Models of Lek Evolution: Data from Three Species of Ungulates [pp. 57-65]Back Matter [pp. A3-A5]!"#$%&'$!(#$()&*+$,-"+./&'"*+$0&&1-1$2('/3-'456#.&'7489$:-*--$;&1('1<&6'=-9$>-.(?"&'(3$@=&3&+A$(*1$<&="&/"&3&+AB$C&3D$EEB$,&D$F$7FGGE8B$HHD$IJKJLM6/3"4.-1$/A9$<H'"*+-'<#(/3-$N:O9$http://www.jstor.org/stable/46008465==-44-19$LIPLIPQLFL$FE9IGYour use of the JSTOR archive indicates your acceptance of JSTOR's Terms and Conditions of Use, available athttp://www.jstor.org/page/info/about/policies/terms.jsp. 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For more information about JSTOR, please contact [email protected] is collaborating with JSTOR to digitize, preserve and extend access to Behavioral Ecology andSociobiology.http://www.jstor.orgBehav Ecol Sociobiol (1993) 33:45-50 Behavioral Ecol Behavioral Ecology and Sociobiology ? Springer-Verlag 1993 Tit for tat among neighboring hooded warblers Renee Godard* Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3280, USA Recieved June 12, 1992 / Accepted in revised form February 1, 1993 Summary. The "dear-enemy" relationship of territorial songbirds could be mutually beneficial to neighbors, as males who recognize neighbors and reduce their re- sponses to these neighbors would require less time and energy for territorial defense. In order for this relation- ship to be evolutionarily stable, this reduction in re- sponse to a neighbor must be conditional on reciprocal restraint by that neighbor. This study examined the pos- sibility of such conditional responses in hooded warblers (Wilsonia citrina). Responses of territorial hooded war- blers to playbacks of neighbors' songs from shared boundaries were measured before and after playbacks that simulated intrusions of those same neighbors (NNNN treatment) or strange birds (NSSN treatment) into the subjects' territories. Each male received both treatments separated by at least 8 days. Males increased their responses to playbacks of a neighbor's songs at the boundary after simulated intrusions of that same neighbor (NNNN) but did not increase their responses to such playbacks after simulated intrusions of strangers (NSSN). This increased response to a "defecting" neigh- bor suggests that the relationship between neighboring territorial hooded warblers is based on a conditional strategy like tit-for-tat. Introduction Established territorial residents often respond less ag- gressively to neighbors than to strangers, a phenomenon known as the "dear-enemy" effect (Fisher 1954; Yden- berg et al. 1988; Qualls and Jaeger 1991; Fox and Baird 1992). In territorial songbirds, this effect is exemplified particularly clearly by the lower responses of residents to neighbors' songs played at an appropriate boundary than to songs of strangers (reviews by Falls 1982; Yden- berg et al. 1988). Reduced aggression toward neighbors, * Present address: Department of Zoology, University of Texas at Austin, Austin, TX 78712, USA once boundaries are established, would have advantages as a territorial resident could reduce its expenditure of time and energy and its risk of injury in frequent excalat- ed encounters. Thus male songbirds might benefit by recognizing and reducing their interactions with neigh- bors. Explanations for the evolution of this behavior have invoked reciprocal altruism based on a strategy of tit- for-tat (TFT) in an iterated Prisoner's Dilemma (Trivers 1971; Axelrod and Hamilton 1981; Trivers 1985; Getty 1987). This explanation raises two related questions: (1) do territorial relationships fit the conditions for recipro- cal altruism as defined by the Prisoner's Dilemma? and (2) do territorial animals' capabilities include conditional strategies like tit-for-tat? It is uncertain that reciprocal altruism actually occurs in situations involving mutual restraint, such as between "dear enemies", because it is difficult to confirm that restraint incurs a cost (Koenig 1988; Rothstein and Pier- otti 1988; Wilkinson 1988; Lombardo 1990). Neverthe- less, it seems plausible that mutual restraint in territorial relationships could often fit the conditions for reciprocal altruism in the Prisoner's Dilemma. Escalated fighting by new territorial neighbors suggests that mutual accep- tance of a boundary involves relinquishing some poten- tial gain from a larger territory (some possibilities might include a larger catchment for obtaining mates, a larger reserve of food, or greater spacing out for protection from predators). If so, the net advantage for an unchal- lenged defector would exceed that for mutual coopera- tors (T> R). In addition, the net advantage for a cooper- ator with a defecting neighbor would fall short of that for mutual defectors that continually contested their boundary (P> S) as a cooperator interacting with defec- tors could potentially lose its mate or territory. Mutual cooperators would presumably do better