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Birds tend to adjust their behavior and physiology to changes in food availability in their environment. Seasonal fluctuation of food resources may act as an energetic challenge, augmenting hypothalamus–pituitary–adrenal axis (HPA axis) activity, leading to an increase in corticosterone concentrations and promoting the metabolism of energy stores. Plant invasions may alter seasonal food fluctuations by providing a food supply during scarce seasons. This could attenuate the energetic challenge, reducing HPA axis activity and the metabolism of reserves. Using a system with seasonal fluctuation in food availability, we tested if fruit supplementation by the invasive fleshy-fruited Pyracantha angustifolia during the season of native fruit scarcity decreases the consumption of energy stores through activity attenuation of the HPA axis. We measured changes in body condition and circulating corticosterone (CORT) concentration in Turdus chiguanco occurring at sites both invaded and not invaded by P. angustifolia over 3 time periods that correspond to the periods prior to, during and after highest fruit production of the plant. Fruit scarcity in the ecosystem appears as an energetic challenge for T. chiguanco, given that body mass, fat score and residuals of body mass/tarsus length decreased during winter in a site not invaded by the exotic shrub. Conversely, the presence of the invasive plant seemed to attenuate the metabolism of energetic reserves, as we did not record changes in body condition in birds inhabiting the invaded site. Unexpectedly, plasma CORT concentration did not vary between sites or periods. Further evaluation is required to elucidate how enhanced body condition, resulting from the consumption of a fleshy-fruited invasive plant, affects survivorship and reproductive performance in T. chiguanco. Fil: Rojas, Tobias Nicolas. Universidad Nacional de Tucumán. Instituto de Ecología Regional. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Ecología Regional; Argentina Fil: Vergara Tabares, David Lautaro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Diversidad y Ecología Animal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Diversidad y Ecología Animal; Argentina Fil: Valdez, Diego Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Diversidad y Ecología Animal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Diversidad y Ecología Animal; Argentina Fil: Ponzio, Marina Flavia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Ciencias de la Salud. Universidad Nacional de Córdoba. Instituto de Investigaciones en Ciencias de la Salud; Argentina Fil: Peluc, Susana Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Diversidad y Ecología Animal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Diversidad y Ecología Animal; Argentina

Forest fragmentation represents a threat to several bird species worldwide. Several factors can change across seasons (e.g. bird perception of the landscape, weather conditions, biotic interactions), which can modify the response of bird populations to forest fragmentation. However, most studies have been conducted only during the breeding season. Here we assessed the relationship between forest fragmentation (patch area and patch isolation) with population abundances of resident species during both the breeding and the non-breeding seasons. Bird population abundances (all species in the community, subsets of forest and habitat generalist species and for individual species) were estimated across a gradient of area-isolation in a semi-arid forest in Cordoba, Argentina. Population abundance of the overall avian community and of the subset of forest species declined with patch area reduction independently of the season. By contrast, the subset of habitat generalist species was not affected by patch area reduction or by the increase in patch isolation, either during the breeding or during the non-breeding season. When the analyses were carried out for individual species, we found four forest species and one habitat generalist species whose responses (the relationship between population abundance and patch area or with isolation) were different between breeding and non-breeding seasons. The negative effects of forest fragmentation were found mainly during the breeding season. Our results suggest that reduction of patch area may lead to a reduction of more than 65% of the population abundance of forest bird species, during both the breeding and the non-breeding season. Therefore, there is an urgent need to conserve large forest patches within the region as irreplaceable elements for the conservation of populations of several species. Fil: Verga, Ernesto Gustavo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Diversidad y Ecología Animal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Diversidad y Ecología Animal; Argentina Fil: Galetto, Leonardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; Argentina Fil: Peluc, Susana Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Diversidad y Ecología Animal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Diversidad y Ecología Animal; Argentina

In avian species living at high altitudes and latitudes, reproductive events are largely controlled by photoperiod, with changes being perceived mainly through encephalic photoreceptors located in the hypothalamus. It is known that during long day periods (reproductive periods), the information transmitted by brain photoreceptors triggers the production of thyroid hormones that regulate GnRH secretion, inducing secretion of pituitary gonadotropins. As a result, gonads develop and grow and the production of gonadal sex hormones, testosterone and estradiol increases (classic gonadal cycle). During short day periods (non-reproductive periods) on the other hand, the gonads regress, and plasma gonadal steroid levels are low. By means of this mechanism, birds synchronize their physiology and reproductive behaviors with seasonal changes in the environment. However, it appears that not all avian species comply with this general reproductive pattern. For example, the Eared Dove (Zenaida auriculata), a South American opportunistic breeding columbiform, has been reported to successfully reproduce throughout the year, making it an interesting avian system for studying the endocrine basis of avian reproduction. In view of a clear lack of seasonal variability in testicular weight and size (the classic gonadal regression/recrudescence cycle) in the male Eared Dove, we examined whether their reproductive aseasonality could be the result of being in a continuous state of reproductive preparedness. Our results show that despite the absence of a marked gonadal cycle in terms of gonadal volume, plasma testosterone levels in males were minimal during autumn-winter, reaching maximum values during spring-summer. This indicates that male gonad function is not seasonal in terms of spermatogenesis but that circulating testosterone levels are correlated with photoperiod, demonstrating an exception to the classic model of reproduction in birds.

Frugivorous birds are able to track spatiotemporal changes in fruit availability. Food resource fluctuations, characteristic of seasonal environments, can be affected by the naturalization of exotic ornithocorous plants. In the mountain forest of central Argentina, invasive shrubs of the genus Pyracantha provide a new temporal resource that modifies fluctuations of natural resource availability because the invasives fructify in autumn-winter (largely uncoupled with the fruiting of native species). The contrasting patterns of resource fluctuation between non-invaded and invaded areas throughout the year provide a good study system to test predictions of the fruit-tracking hypothesis, and to understand the relationship between food resources offered by fleshy fruited invasives and abundances of avian trophic guilds. By means of point counts conducted during five time periods at invaded and non-invaded sites we found that the presence of Pyracantha, and time periods, significantly affected frugivorous bird abundance, which in autumn-winter was greater in invaded sites and in spring-summer similar between invaded and non-invaded sites. On the other hand, granivores and insectivores did not show a significant relationship with the presence of Pyracantha. Abundances of the most common seed disperser were significantly affected by the interaction between time period and presence of Pyracantha. These results indicate that the abundances of birds that legitimately disperse Pyracantha seeds are temporally and spatially associated with fruit abundance provided by this exotic plant. This underscores fruit availability as an important ecological factor affecting frugivorous bird abundance, and suggests that Pyracantha seed dispersers are capable of detecting changes in the availability of its fruit, likely contributing to the effectiveness of its dispersal.

Forest fragmentation threatens bird species throughout the world. Previous studies suggest that the sensitivity of bird species to forest fragmentation is related to food abundance, and that this could be a key factor in understanding demographic changes. We assessed the relationship between forest fragment size, isolation and food abundance and the abundance of seven common species of birds in southern Chaco forests of Argentina, which use different food items, and are involved in different ecosystem processes. Relative abundance of Turdus amaurochalinus (Creamy-bellied Thrush) and Saltator aurantiirostris (Golden-billed Saltator) significantly decreased with patch size reduction, whereas relative abundance of Taraba major (Great Antshrike) decreased with patch isolation and increased with arthropod abundance. Chlorostilbon lucidus (Glittering-bellied Emerald), Elaenia parvirostris (Small-billed Elaenia), Polioptila dumicola (Masked Gnatcatcher) and Zonotrichia capensis (Rufous-collared Sparrow) appeared to be resilient to forest fragmentation. Body size was a good predictor of bird sensitivity, as only the largest species were negatively correlated with forest fragmentation. Previous work suggests that birds inhabiting Chaco forests may be resilient to forest fragmentation. This needs to be reconsidered in the light of our results since the abundance of three out of seven common bird species were negatively related to forest fragmentation. Fil: Verga, Ernesto Gustavo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; Argentina Fil: Sanchez Humoller, Hilda Leticia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; Argentina Fil: Peluc, Susana Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Diversidad y Ecología Animal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Diversidad y Ecología Animal; Argentina Fil: Galetto, Leonardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; Argentina

Mechanisms underlying biological invasion of highly disturbed ecosystems are well known, yet mechanisms responsible for biological invasion of undisturbed or weakly disturbed ecosystems are less understood. The triggering attribute (TA) approach, proposed as a mechanism that explains plant invasion success in undisturbed or weakly disturbed systems, considers that the spread of alien species depends on specific vegetative or regenerative traits in invasive species, discontinuously distributed in comparison to the resident community. In mountain Chaco woodland, fruiting phenology of ornithocorous invasive plants has been proposed as a TA, because it would allow invasive species to benefit from seed dispersal service, which is unused by native plants during a specific period of the year (winter). Under the seed dispersal ecology framework, we evaluated if fruiting phenology (fructification largely uncoupled with native species) of the fleshy-fruited invasive Pyracantha angustifolia affects bird fruit consumption, and allows the invasive to take advantage of the unused seed dispersal service during winter. If uncoupled fructification phenology represents a TA, seed disperser, seed predator, and pulp consumer diversity, abundance, and fruit consumption on P. angustifolia (which fructifies in winter), will be higher than on its exotic congeneric P. coccinea during summer, when fructification overlaps with native Celtis ehrenbergiana and many other native species. We found that: (1) disperser bird abundance and fruit consumption did not differ between P. angustifolia and P. coccinea; (2) the most diverse frugivorous assemblage was observed on C. ehrenbergiana, yet it had the lowest proportion of seed dispersers and the highest fruit consumption by seed predators and, (3) we also observed higher proportion of seed predators on P. angustifolia (uncoupled fructification scenario) than on P. coccinea (coupled fructification scenario). Our results suggest that invasive uncoupled fructification phenology does not represent a true TA which facilitates plant invasion processes in undisturbed or weakly disturbed ecosystem. Fil: Vergara Tabares, David Lautaro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Diversidad y Ecología Animal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Diversidad y Ecología Animal; Argentina Fil: Badini, Julieta. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Zoología Aplicada; Argentina Fil: Peluc, Susana Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Diversidad y Ecología Animal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Diversidad y Ecología Animal; Argentina

La pérdida y fragmentación del bosque pueden alterar la abundancia de recursos alimentarios que consumen distintos grupos de aves. Estudiar cómo se relacionan distintos indicadores de la fragmentación con la abundancia de alimentos consumidos por una amplia diversidad de aves puede ayudar a entender los efectos indirectos de la fragmentación del bosque sobre sus poblaciones. Trabajamos en fragmentos de bosque chaqueño en Córdoba, Argentina. Estimamos la abundancia relativa de artrópodos, flores, frutos y semillas (alimento para distintos gremios trófcos de aves) en un gradiente de fragmentación, tanto en verano como en invierno. Durante el verano, Celtis ehrenbergiana y Lycium cestroides ofrecieron más del 90% de los frutos y flores estimados, respectivamente. Durante el invierno, Solanum argentinum aportó casi la totalidad de los frutos ornitócoros estimados. La abundancia de artrópodos (durante el invierno) y de semillas (en ambas estaciones) aumentó con la reducción del área de los fragmentos y se observó una mayor abundancia en el borde respecto al interior de los fragmentos. Sólo observamos una relación negativa entre la fragmentación y la abundancia de frutos ornitócoros y flores ornitóflas para algunas especies individuales. Con respecto a la estacionalidad, la abundancia relativa de artrópodos fue signifcativamente menor durante el invierno, mientras que la abundancia relativa de frutos ornitócoros y semillas en el suelo fue similar entre estaciones. La disminución de la abundancia de flores en invierno fue tan drástica que nos imposibilitó realizar comparaciones estadísticas. Este trabajo ofrece una primera aproximación a la abundancia de recursos alimentarios que consumen las aves y su respuesta a la fragmentación en un sector del bosque chaqueño. Forest loss and fragmentation can affect food resources consumed by different avian groups. A better knowledge on the relationships between different proxies of forest fragmentation and food resources consumed by a wide diversity of avian species can help us understand the indirect effects of forest fragmentation on bird populations. We worked in forest patches in the Chaco forest of Córdoba, Argentina. We estimated the relative abundance of arthropods, flowers, fruits and seeds (food items for different bird feeding guilds) in a fragmentation gradient during summer and winter. During the summer season, Celtis ehrenbergiana and Lycium cestroides offered >90% of the total fruits and flowers estimated abundance, respectively. Solanum argentinum offered most of the estimated fruit abundance during the winter season. Arthropod abundance (in winter) and seed abundance (in both seasons) increased with patch size reduction; moreover, we observed higher abundance in the forest edge than in the interior. We only found a negative effect of forest fragmentation on fruit and flower abundance for individual species. Regarding to seasonality, relative abundance of arthropods was significantly reduced in winter, whereas relative abundance of fruit and seeds was similar between seasons. Relative abundance of flowers was drastically reduced in winter; therefore, we could not perform statistical comparisons between seasons. This work offers a first approach to the food abundance resources for birds and their response to fragmentation in an area of the Chaco forests.

We analysed the temporal occurrence (day–night) and timing of nest predation events during incubation for six common passerine species breeding in austral Chaco, a temperate South American habitat. We recorded time of predation events and incubation parental care activity using temperature sensors (data validated by field observations of nest fate) for 187 nests. The temporal occurrence of 35 predation events (77% during the day and 23% overnight) suggests a predator assemblage likely dominated by diurnal predators. Greater nest parental activity occurred early in the morning (06 00–09 00h) and late afternoon (17 00–20 00h), coinciding with a greater number of predation events. However, the relationship between the number of parental trips to a nest and its incidence on nest predation was not significant. Likewise, for Golden-billed Saltator, with parental activity and predation patterns similar to those of the group of species as a whole, nest parental activity was not significantly related to nest success/predation fate during incubation. Even though patterns of parental activity and predation events throughout the day seem alike, the lack of statistical relationship between such variables casts doubts regarding the influence of nest predation on parental behaviours during incubation in the species studied here. Fil: Schaaf, Alejandro Alberto. Universidad Nacional de Jujuy. Instituto de Ecorregiones Andinas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Ecorregiones Andinas; Argentina Fil: Vergara Tabares, David Lautaro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Diversidad y Ecología Animal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Diversidad y Ecología Animal; Argentina Fil: Peralta, Giovana Claudia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Diversidad y Ecología Animal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Diversidad y Ecología Animal; Argentina Fil: Diaz, Agustín Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Diversidad y Ecología Animal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Diversidad y Ecología Animal; Argentina Fil: Peluc, Susana Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Diversidad y Ecología Animal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Diversidad y Ecología Animal; Argentina

Maternal resources deposited in eggs can aff ect the development of several off spring phenotypic traits and result in tradeoff s among them. For example, maternal androgens in eggs may be benefi cial to off spring growth and competitive ability, but detrimental to immunocompetence and oxidative stress. In contrast, maternal antioxidants in eggs may be benefi cial if they mitigate oxidative stress and immunosuppressive eff ects of androgens. We investigated possible interactive eff ects of maternal steroids and carotenoids on aspects of off spring physiology and phenotype, by simultaneously manipulating levels of androgens (via gonadotropin-releasing hormone, GnRH-challenges) and carotenoids (via diet supplementation) in captive female Japanese quail Coturnix japonica during egg laying. Carotenoid supplementation of hens, which elevates yolk concentrations of carotenoid and vitamins A and E, enhanced egg hatching success, off spring survival to age 15 d, and size of the bursa of Fabricius in off spring. In contrast, repeated maternal GnRH challenges, which elevated yolk testosterone concentrations, enhanced off spring neonatal size, but negatively aff ected bursa size. However, interaction among the treatments suggests that the positive eff ect of maternal carotenoid supplementation on plasma bactericidal capacity was mediated by maternal GnRH challenges. Chicks originating from carotenoid-supplemented hens were less immunosuppressed than those originating from carotenoid-supplemented GnRH-challenged hens, which were less immunosuppressed than chicks from GnRH-challenged females not supplemented with carotenoids. Females availability of carotenoid enriched diets allows them to enhance the development of off spring immune system via carotenoids and vitamins deposited in egg yolks and off set detrimental eff ects of androgens deposited by GnRHchallenged females.

Spatial and temporal variation in resource abundance and predation risk can favor the evolution of phenotypic plasticity as a means of tracking changing environments. However, because food abundance and predation risk often covary in nature, few studies have separated their effects or tested whether different phenotypic traits respond to the same sources of environmental variation. We investigated patterns of parental investment and behavior over a 7-year period in 2 island populations of orange-crowned warblers (Oreothlypis celata) that showed little genetic divergence but experienced dramatic temporal variation in rainfall and spatial variation in nest predation risk. The amount of rainfall in each year was correlated with food abundance, and birds on both islands initiated breeding earlier and laid larger clutches in wetter years. In contrast, the rate at which parents visited their nests was not affected by rainfall but was negatively correlated with nest predation risk both within and between islands. Our results suggest that although the effects of food availability and nest predation have been viewed as mutually exclusive drivers of entire suites of life-history and behavioral traits, these traits can differ in their sensitivity to resource abundance or mortality risk, and traits that are often correlated can be decoupled under appropriate environmental conditions. Key wor ds: breeding phenology , clutch size, life-history strategies, parental care, phenotypic plasticity. [Behav Ecol]

In 2005, Gurvich et al. proposed that once a nonindigenousspecies has arrived to a new ecosystem andbecome established, the likelihood that it spreads, andthus becomes invasive, may depend on just one or veryfew characteristics, called ?triggering attributes? (TA).We propose that a TA is a vegetative or regenerativeattribute discontinuously distributed in comparison tothe resident community. This attribute allows thespecies to benefit from a resource that is permanentlyor temporarily unused by the resident community. The winter fruit phenology of two fleshy fruitedinvaders (P. angustifolia and Ligustrum lucidum) wasproposed as an example of TA that would allow thesetwo species to take advantage of a resource (birddispersal) that resident fleshy-fruited species?whosefruits are ripe in summer and autumn cannot tapduring the winter (Gurvich et al. 2016). We believethat the model they proposed is a very valuable one,and useful to identify special traits involved in plantinvasion processes. In a recent response to an articlethat evaluates if a vegetative attribute behaves as a TA(Vergara-Tabares et al. 2015), Gurvich et al. (2016)expressed disagreement regarding the logic used todevelop the experimental design and the main conclusionsof the study. The arguments of Gurvich et al.(2016) demonstrate some misinterpretation of thestudy and its results, and we believe it deservesclarification. Fil: Vergara Tabares, David L.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Diversidad y Ecología Animal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Diversidad y Ecología Animal; Argentina Fil: Badini, Julieta. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; Argentina Fil: Peluc, Susana Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Diversidad y Ecología Animal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Diversidad y Ecología Animal; Argentina

Avian nest site selection and levels of parental care require assessments of numerous fitness costs and benefits. Nest site selection in open cup--nesting species is considered a relatively conservative trait; most species and genera are confined to nesting within particular vegetation strata. The nesting stratum further determines risk to nest predation, the principal cause of reproductive failure. We document predator-induced plasticity in nest site placement and levels of parental care in orange-crowned warblers (Vermivora celata) on an island lacking avian nest predators. We show a shift from ground nesting, characteristic of mainland populations, to off-ground nesting that appears adaptive relative to higher predation levels of ground nests. By altering the perceived nest predation risk via experimental introduction of a model avian predator prior to nest building, we demonstrate that warblers shift nest sites to more concealed ground locations. Moreover, warblers differentially adjust nest visits to feed nestlings in the presence of the predator: reducing feeding more at less concealed off-ground nests than at more concealed ground ones. Both shifts in nest site placement and feeding rate adjustments suggest adaptive phenotypic plasticity in response to increased perceived predation risk, providing evidence that birds continuously assess variation in the fitness costs and benefits of their behavioral decisions. Copyright 2008, Oxford University Press.

Androgens and carotenoids circulating in plasma affect the physiology and behavior of vertebrates. Much is known about control mechanisms and functions of each of these substances, yet their interactive effects are not well understood. Here we examine possible additive, multiplicative, and interactive effects of testosterone and carotenoids on female endocrine physiology, immunocompetence, and investment in eggs by simultaneously manipulating levels of testosterone [via gonadotropin releasing hormone (GnRH) challenges] and carotenoids (via diet supplementation) in captive female Japanese quail (Coturnix japonica). Females were randomly assigned to one of four treatments: carotenoid supplementation, GnRH challenge, GnRH challenge + carotenoid supplementation, or control. Carotenoid supplementation significantly increased circulating plasma carotenoid levels and acquired immune system performance, but not innate immunity. GnRH challenges elevated circulating testosterone and carotenoid levels, and induced immunosuppression in females. However, females in the GnRH challenge + carotenoid supplementation treatment had higher cell-mediated immune responses than control females and similar responses to those of carotenoid-supplemented females. Hence, availability of carotenoids in female quail seemed to counteract immunosuppressive effects of GnRH challenges. Our results provide further evidence for synergistic effects of carotenoids and testosterone on endocrine physiology and immune function in female birds. Elevated plasma testosterone or carotenoids levels resulted in increased deposition of those compounds to eggs, respectively. Furthermore, because we found that concentrations of testosterone and carotenoids in yolks were correlated within each treatment group, differential deposition of hormones and carotenoids in eggs may not only respond to surrounding social and environmental conditions, but also to other components of the egg.