Breeding southern house wrens exhibit a threat-sensitive response when exposed to different predator models

We assessed the ability of southern house wrens (Troglodytes aedon musculus) to recognize and discriminate different birds of prey. We exposed nesting birds to stuffed specimens of two sympatric predator species, the chimango caracara (Milvago chimango, a nest predator) and the roadside hawk (Buteo magnirostris, a predator of adults and nests), and to a dummy of a non-sympatric predator, the double-toothed kite (Harpagus bidentatus, a predator of adults). Nesting wrens avoided going into their nest or took a longer time to resume their parental duties when exposed to the predators than when they were exposed to a control dummy (Chrysomus ruficapillus, a sympatric blackbird). Nest avoidance was higher when birds were exposed to the roadside hawk but no differences were detected when exposed to the chimango caracara or the double-toothed kite. The results indicate that southern house wrens are able to recognize a predator, responding in a graded manner. Our findings support the hypothesis that southern house wrens exhibit a threat-sensitive response during breeding. Also, individuals were able to recognize the unknown predator but failed to correctly assess the threat level represented by it. We propose that correct assessment of threat level by house wrens requires direct experience with the predator, which might mediate in the modulation of the response.Fil: Duré Ruiz, Natalia Mabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; ArgentinaFil: Fasanella, Mariana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Fernandez, Gustavo Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentin

Failure of captive-born greater rheas (Rhea americana, Rheidae, Aves) to discriminate between predator and nonpredator models

The capacity to recognize and respond to predators can be lost by captive animals. Habituation to humans caused by the captive environment can be transferred to other stimuli, such as predators, a situation that conservation biologists wish to avoid. Greater rheas are threatened South American birds, for which there are plans for reintroduction programs in Brazil. The goal of this study was to evaluate the behavioral responses of captive-born greater rheas to different models of predators and nonpredators. Seventeen captive-born greater rheas, divided into four groups, from the Belo Horizonte Zoo, Brazil were studied. Three predator and three nonpredator models were presented to the birds and their behavioral responses recorded. Predators versus nonpredator models and the behavior of rheas in three experimental phases (baseline, models, and postmodels) were analyzed. Captive-born greater rheas modified their behaviors in the presence of both predator/nonpredator models, increasing alert and wary behaviors (alert, observing, and pacing behaviors: P<0.01), showing some degree of antipredator behavior persistence, but they were unable to discriminate between predator and nonpredator models (all behaviors: P>0.05). In conclusion, antipredator training should be implemented to develop the expression of this behavior before reintroductions are attempted

Offspring reproductive value and nest defense in the magpie (Pica pica)

Magpie (Pica pica) brood defense against a human at the nest was studied in a Mediterranean population with low renesting potential. Variations in two defense measures recorded during 106 trials at 41 different nests were positively correlated with brood age. Ineremental effects due to the number of successive visits to nests by us, brood size, and the time in the breeding season were not significant. Partial correlation analyses showed that visit rate was not an important determinant of nest defense, which thus favors an adaptive explanation of nest defense patterns. Two functional hypotheses to account for the increase in defense intensity with brood age were tested: whether (1) increased parental defense serves to compensate the higher predation risk of older nests or (2) increased parental defense reflects the increasing reproductive value of nestlings as they grow older. Daily mortality and incidende of predation (estimated from contribution of whole-brood losses to total mortality) was higher early in the nestling period, hence providing weak evidence for the assumption on which hypothesis (1) is based. The timing of parental defense intensity did not mirror variations in predation risk for the nest but variations in reproductive value of the brood, as can be estimated from daily mortality, thus supporting hypothesis (2). Magpie parents increased defense intensity in response to premature escaping by almost fully-developed nestlings. Since such a response lowers predation risk for the offspring and increases their probability of survival, this finding supports hypothesis (2), but runs contrary to hypothesis (1). Parents also increased defense in response to play-backs of alarm calls uttered by nestlings during escaping episodes. It is argued that parents should continuously monitor the degree of offspring development in order to assess their reproductive value and that, by alarm calling, chicks honestly make their parents aware of the gain in reproductive value that results from enhancement in locomotory abilities that occur at the end of the nestling period. Behavioral Ecology and Sociobiology Behavioral Ecology and Sociobiology Look Inside Other actionsPeer reviewe