Experimental analysis of novelty responses in a bird assemblage inhabiting a suburban marsh A.I. Echeverrı´a, Aldo Iva ´n Vassallo, and J.P. Isacch Abstract: Suburban areas in the Pampas region of Argentina are inhabited by several bird species that sharply differ in their ability to exploit human-modified, urban areas. This bird assemblage includes species restricted to natural grasslands (e.g., Great Pampa Finch, Embernagra platensis (J.F. Gmelin, 1789)) as well as generalist, highly cosmopolitan species such as House Sparrow, Passer domesticus (L., 1758). We explored the role of certain aversive responses to novelty in shaping the marked differences in ecological plasticity among species in the assemblage. In field experiments, we tested for differences in feeding in the presence of artificial objects near feeders regularly replenished with seeds. In spite of their granivorous diet, some non-urbanized species did not use the feeders, possibly because of an extreme degree of aversion to novel situations. The group of birds that visited the feeders included both urbanized (N = 8) and non-urbanized (N = 2) species. We found that the presence of novel objects discouraged visitation to an otherwise attractive food source, although neophobia was weak for most species. However, we found unexpectedly high levels of neophobia in highly generalist, urbanized species such as House Sparrow and Shiny Cowbird, Molothrus bonariensis (J.F. Gmelin, 1789). This response is discussed in the context of the influence of post-fledging development in a relatively simple and predictable ecosystem versus that in urban areas. Re ´sume ´: Les banlieues de la re ´gion des Pampas en Argentine sont colonise ´es par plusieurs espe `ces d’oiseaux qui diffe `r- ent grandement par leur capacite ´a ` exploiter les re ´gions urbaines modifie ´es par la pre ´sence humaine. Ce peuplement inclut des espe `ces restreintes aux steppes naturelles, par exemple, l’embernagre a ` cinq couleurs, Embernagra platensis (J.F. Gme- lin, 1789), ainsi que des espe `ces ge ´ne ´ralistes tre `s cosmopolites, telles que le moineau domestique, Passer domesticus (L., 1758). Nous avons explore ´ le ro ˆle de certaines re ´actions adverses a ` la nouveaute ´ dans l’e ´tablissement des diffe ´rences mar- que ´es de plasticite ´e ´cologique chez les diverses espe `ces du peuplement. Dans des expe ´riences de terrain, nous avons ve ´ri- fie ´ l’existence de diffe ´rences de comportements alimentaires en pre ´sence d’objets artificiels place ´s pre `s des mangeoires remplies de graines a ` intervalles re ´guliers. Malgre ´ leur re ´gime alimentaire granivore, quelques espe `ces non urbanise ´es n’utilisent pas les mangeoires, probablement a ` cause de leur aversion extre ˆme a ` des situations ine ´dites. Le groupe d’oi- seaux qui utilise les mangeoires comprend des espe `ces urbanise ´es (N = 8) ainsi que des espe `ces non urbanise ´es (N = 2). La pre ´sence d’objets inhabituels de ´courage l’utilisation d’une source de nourriture par ailleurs inte ´ressante, bien que la phobie de la nouveaute ´ soit faible chez la plupart des espe `ces. Cependant, il existe de fac ¸on tout a ` fait inattendue un fort degre ´ de ne ´ophobie chez certaines espe `ces ge ´ne ´ralistes et fortement urbanise ´es, telles que le moineau domestique et le vacher luisant, Molothrus bonariensis (J.F. Gmelin, 1789). Nous discutons de cette re ´action dans le cadre de l’influence du de ´veloppement apre `s l’envol dans un e ´cosyste `me simple et pre ´visible, par comparaison aux zones urbaines. [Traduit par la Re ´daction] Introduction One of the main goals of behavioral ecology is to relate behavior at the individual level with the ecological niche oc- cupied by species. Several studies have shown that there is considerable inter-individual variability in many aspects of behavior, even when animals are reared under similar condi- tions (Skutch 1996; Krebs and Davies 1998). Behavioral flexibility has been implicated as being important in deter- mining the probability of invasion of a new adaptive zone during diversifying processes (Greenberg 1990; Foster and Endler 1999) and may also explain differences in bird spe- cies richness (Nicolakakis et al. 2003) and invasion success (Sol et al. 2002). Behavioral flexibility plays a critical role because individ- uals that can vary their behavior will respond much more rapidly than others when confronted with a changing envi- ronment or new ecological opportunities (Reader 2003). An- imals that sample novel microhabitats may be more able to exploit new foraging opportunities when searching for food (Coleman and Mellgren 1994). Compared with more speci- alized species, generalist organisms exploit a greater variety of food items and consequently have a greater probability of encountering novel stimuli associated with food. Individuals can be attracted (neophilia) or deterred (neophobia) by novel stimuli. Neophobia, the aversive response to a novel stimu- lus or circumstance, may be of importance in determining an individual’s behavioral flexibility. Variation in the intensity of aversive responses may influence the probability that an individual will explore and locate unfamiliar resources (the Received 7 March 2006. Accepted 24 May 2006. Published on the NRC Research Press Web site at http://cjz.nrc.ca on 12 August 2006. A.I. Echeverrı ´a, A.I. Vassallo, 1 and J.P. Isacch. Departamento de Biologı ´a, Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Mar del Plata, Casilla de correo 1245, Consejo Nacional de Investigaciones Cientı ´ficas y Te ´cnicas (CONICET), 7600 Mar del Plata, Argentina. 1 Corresponding author (e-mail: avassall@mdp.edu.ar). 974 Can. J. Zool. 84: 974–980 (2006) doi:10.1139/Z06-089 # 2006 NRC Canada