Effects of land use on riparian birds in a semiarid region

We investigated the influence of landscape characteristics on avian species occupancy in riparian forests embedded in a matrix of urban and agricultural land use in a semiarid region of the Southwestern US. We conducted bird and vegetation (local-scale characteristics) surveys within 196 50-m radius sample points in 10 riparian forests in southern California. We quantified landscape composition within a 500m-radius surrounding each point. For each species we developed 8 single-season occupancy models using principal components summarizing local- and landscape-scale characteristics and a spatial autocovariate as covariates. Of 21 species analyzed, occupancy by 11 was associated with landscape characteristics, by 6 with local vegetation characteristics, by 3 with both local and landscape characteristics, and by 1 with none. Five species positively responded to surrounding urban development (2 negative), whereas 4 negatively responded to agricultural land (1 positive). The amount of riparian forests had a strong positive effect on the occurrence of riparian obligates. Our results emphasize the importance of landscape characteristics on species occupancy patterns in riparian systems although relationships were also species-specific. Our results imply a positive effect of urbanization compared to agricultural land uses in this region, most likely due to enhanced vegetation development

Phenotypic plasticity in nest departure calls: Weighing costs and benefits

In birds, male song has been extensively studied, but female vocalizations have received little attention. Females of several North American species produce a unique vocalization, the nest departure call (NDC), upon leaving nests. Producing NDCs has costs due to acoustical properties that make nests easy to locate by predators. Thus, NDCs must also have benefits that balance or outweigh costs, and females should modulate call production as costs and benefits change. We explored whether female song sparrows, Melospiza melodia, adjust calling rate to reflect differential costs and benefits of calling induced by male presence, male quality (measured by body mass and song complexity), nest predator presence and nest height. Results suggest that calls benefit females by promoting male nest guarding and that females display adaptive plasticity in call production. Specifically, calling rate increased when the male was present, and male nest guarding increased when females gave an NDC. Females called less in the presence of a model nest predator, probably because the perceived costs of predator attraction outweighed the benefits of male recruitment. Conversely, females with heavier mates called more, perhaps because the efficacy of male nest guarding increases with mass. In addition, females called more from elevated nests in the presence of the predator and decreased calling later in the day. Male song complexity failed to predict calling rate, suggesting that this sexually selected trait does not reflect direct benefits gained by producing an NDC. Plasticity in calling probably exists because context-appropriate communication elevates fitness, whereas contextual mistakes in the decision to communicate result in fitness declines. © 2014 The Association for the Study of Animal Behaviour

Phaeomelanin- and carotenoid-based pigmentation reflect oxidative status in two populations of the yellow warbler (Setophaga petechia)

Carotenoid- and phaeomelanin-based sexual pigmentation may signal a capacity to maintain oxidative balance and viability. However, diverse empirical results leave the association between pigmentation and oxidative stress (OS) unclear. We assessed the hypothesis that population-specific levels of oxidative challenge, or strategies for managing OS, affect relationships between sexual pigmentation and OS. Specifically, intense oxidative challenge in migratory, temperate breeding birds might enhance correlations between pigmentation and OS relative to allied tropical breeders, since quality-based differences in OS may arise only under intense oxidative challenge. Alternatively, in temperate breeders with intense within-season reproductive effort, high-quality birds may invest in reproduction over oxidative balance, dampening negative correlations between pigmentation and OS. To assess these alternatives, we compared prenesting relationships between pigmentation and OS in a migratory, Californian population of yellow warblers (Setophaga petechia brewsteri) and in a resident, Mexican population (Setophaga petechia bryanti, "mangrove warblers"). Yellow warblers displayed higher OS than mangrove warblers. However, year of capture and sex had bigger influences on correlations between pigmentation and OS than population. Males with more intense melanin pigmentation had lower OS among mangrove warblers and yellow warblers captured in 2011, but not among yellow warblers captured in 2012. In females only, lower OS levels were associated with more colorful carotenoid pigmentation. Results suggest that both phaeomelanin- and carotenoid-based pigmentation have the potential to correlate with OS levels, but that the signaling potential of pigmentation may shift with inter-annual variation in environmental conditions and display sex-specific dynamics. © 2014 Springer-Verlag Berlin Heidelberg

Pigment-specific relationships between feather corticosterone concentrations and sexual coloration

The adrenocortical stress response may divert energy away from sexual ornamentation, such that ornaments signal exposure or resistance to physiological stress. Alternatively, steroid glucocorticoids released via the stress response may support ornament development by stimulating foraging and metabolism. The relationship between glucocorticoids and ornamentation may vary with ornament type and across age and sex classes that experience different resource allocation tradeoffs. In yellow warblers (Setophaga petechia), we conducted the first study to simultaneously assess whether relationships between corticosterone (the primary avian glucocorticoid) and ornamentation depend on sexual pigment type, age, and sex. We quantified carotenoid- and phaeomelanin-based pigmentation using spectrometry, and assayed corticosterone in feathers (CORTf) to derive an integrative metric of corticosterone levels during molt. Yellow warblers with lower carotenoid hue (lambda R50) had higher CORTf, suggesting that carotenoid hue may signal stress during molt across age and sex classes. Carotenoid chroma also negatively correlated with CORTf. However, this correlation was absent in older males, seemingly because these males display more saturated carotenoid pigmentation, and thus less variance in carotenoid chroma. Young males with higher CORTf also tended to have poorer quality tertial feathers, indicating poor condition at molt. Phaeomelanin-based pigmentation was largely unrelated to CORTf, suggesting that pleiotropic effects do not link phaeomelanogenesis and CORT release. Finally, CORTf was repeatable across years within individuals. Thus, carotenoid- and phaeomelanin-based pigmentation communicate nonequivalent information about physiological stress, with carotenoid pigmentation having the potential to signal stable differences in stress levels that could affect fitness

Re-Shuffling of Species with Climate Disruption: A No-Analog Future for California Birds?

By facilitating independent shifts in species' distributions, climate disruption may result in the rapid development of novel species assemblages that challenge the capacity of species to co-exist and adapt. We used a multivariate approach borrowed from paleoecology to quantify the potential change in California terrestrial breeding bird communities based on current and future species-distribution models for 60 focal species. Projections of future no-analog communities based on two climate models and two species-distribution-model algorithms indicate that by 2070 over half of California could be occupied by novel assemblages of bird species, implying the potential for dramatic community reshuffling and altered patterns of species interactions. The expected percentage of no-analog bird communities was dependent on the community scale examined, but consistent geographic patterns indicated several locations that are particularly likely to host novel bird communities in the future. These no-analog areas did not always coincide with areas of greatest projected species turnover. Efforts to conserve and manage biodiversity could be substantially improved by considering not just future changes in the distribution of individual species, but including the potential for unprecedented changes in community composition and unanticipated consequences of novel species assemblages

Avian Use of Perennial Biomass Feedstocks as Post-Breeding and Migratory Stopover Habitat

Increased production of biomass crops in North America will require new agricultural land, intensify the cultivation of land already under production and introduce new types of biomass crops. Assessing the potential biodiversity impacts of novel agricultural systems is fundamental to the maintenance of biodiversity in agricultural landscapes, yet the consequences of expanded biomass production remain unclear. We evaluate the ability of two candidate second generation biomass feedstocks (switchgrass, Panicum virgatum, and mixed-grass prairie) not currently managed as crops to act as post-breeding and fall migratory stopover habitat for birds. In total, we detected 41 bird species, including grassland specialists and species of state and national conservation concern (e.g. Henslow's Sparrow, Ammodramus henslowii). Avian species richness was generally comparable in switchgrass and prairie and increased with patch size in both patch types. Grassland specialists were less abundant and less likely to occur in patches within highly forested landscapes and were more common and likely to occur in larger patches, indicating that this group is also area-sensitive outside of the breeding season. Variation in the biomass and richness of arthropod food within patches was generally unrelated to richness and abundance metrics. Total bird abundance and that of grassland specialists was higher in patches with greater vegetation structural heterogeneity. Collectively, we find that perennial biomass feedstocks have potential to provide post-breeding and migratory stopover habitat for birds, but that the placement and management of crops will be critical factors in determining their suitability for species of conservation concern. Industrialization of cellulosic bioenergy production that results in reduced crop structural heterogeneity is likely to dramatically reduce the suitability of perennial biomass crops for birds

Connecting species’ geographical distributions to environmental variables: range maps versus observed points of occurrence

Connecting the geographical occurrence of a species with underlying environmental variables is fundamental for many analyses of life history evolution and for modeling species distributions for both basic and practical ends. However, raw distributional information comes principally in two forms: points of occurrence (specific geographical coordinates where a species has been observed), and expert-prepared range maps. Each form has potential short-comings: range maps tend to overestimate the true occurrence of a species, whereas occurrence points (because of their frequent non-random spatial distribution) tend to underestimate it. Whereas previous comparisons of the two forms have focused on how they may differ when estimating species richness, less attention has been paid to the extent to which the two forms actually differ in their representation of a species’ environmental associations. We assess such differences using the globally distributed avian order Galliformes (294 species). For each species we overlaid range maps obtained from IUCN and point-of-occurrence data obtained from GBIF on global maps of four climate variables and elevation. Over all species, the median difference in distribution centroids was 234 km, and median values of all five environmental variables were highly correlated, although there were a few species outliers for each variable. We also acquired species’ elevational distribution mid-points (mid-point between minimum and maximum elevational extent) from the literature; median elevations from point occurrences and ranges were consistently lower (median −420 m) than mid-points. We concluded that in most cases occurrence points were likely to produce better estimates of underlying environmental variables than range maps, although differences were often slight. We also concluded that elevational range mid-points were biased high, and that elevation distributions based on either points or range maps provided better estimates

Phenotypic plasticity in nest departure calls: Weighing costs and benefits

In birds, male song has been extensively studied, but female vocalizations have received little attention. Females of several North American species produce a unique vocalization, the nest departure call (NDC), upon leaving nests. Producing NDCs has costs due to acoustical properties that make nests easy to locate by predators. Thus, NDCs must also have benefits that balance or outweigh costs, and females should modulate call production as costs and benefits change. We explored whether female song sparrows, Melospiza melodia, adjust calling rate to reflect differential costs and benefits of calling induced by male presence, male quality (measured by body mass and song complexity), nest predator presence and nest height. Results suggest that calls benefit females by promoting male nest guarding and that females display adaptive plasticity in call production. Specifically, calling rate increased when the male was present, and male nest guarding increased when females gave an NDC. Females called less in the presence of a model nest predator, probably because the perceived costs of predator attraction outweighed the benefits of male recruitment. Conversely, females with heavier mates called more, perhaps because the efficacy of male nest guarding increases with mass. In addition, females called more from elevated nests in the presence of the predator and decreased calling later in the day. Male song complexity failed to predict calling rate, suggesting that this sexually selected trait does not reflect direct benefits gained by producing an NDC. Plasticity in calling probably exists because context-appropriate communication elevates fitness, whereas contextual mistakes in the decision to communicate result in fitness declines. © 2014 The Association for the Study of Animal Behaviour