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Abstract The development of inexpensive and portable point‐of‐care devices for measuring nutritional physiological parameters from blood (e.g., glucose, ketones) has accelerated our understanding and assessment of real‐time variation in human health, but these have infrequently been tested or implemented in wild animals, especially in relation to other key biological or fitness‐related traits. Here we used point‐of‐care devices to measure blood levels of glucose, ketones, uric acid, and triglycerides in free‐ranging house finches (Haemorhous mexicanus)—a common songbird in North America that has been well‐studied in the context of urbanization, nutrition, health, and sexual selection—during winter and examined (1) repeatability of these methods for evaluating blood levels in these wild passerines, (2) intercorrelations among these measurements within individuals, (3) how blood nutritional‐physiology metrics related to a bird's body condition, habitat of origin (urban vs. suburban), poxvirus infection, and sex; and (4) if the expression of male sexually selected plumage coloration was linked to any of the nutritional‐physiological metrics. All blood‐nutritional parameters were repeatable. Also, there was significant positive covariation between concentrations of circulating triglycerides and glucose and triglycerides and uric acid. Urban finches had higher blood glucose concentrations than suburban finches, and pox‐infected individuals had lower blood triglyceride concentrations than uninfected ones. Last, redder males had higher blood glucose, but lower uric acid levels. These results demonstrate that point‐of‐care devices can be useful, inexpensive ways of measuring real‐time variation in the nutritional physiology of wild birds. 

Abstract Animals inhabiting urban areas often experience elevated disease threats, putatively due to factors such as increased population density and horizontal transmission or decreased immunity (e.g. due to nutrition, pollution, stress). However, for animals that take advantage of human food subsidies, like feeder-visiting birds, an additional mechanism may include exposure to contaminated feeders as fomites. There are some published associations between bird feeder presence/density and avian disease, but to date no experimental study has tested the hypothesis that feeder contamination can directly impact disease status of visiting birds, especially in relation to the population of origin (i.e. urban v. rural, where feeder use/densities naturally vary dramatically). Here we used a field, feeder-cleaning experimental design to show that rural, but not urban, house finches ( Haemorhous mexicanus ) showed increased infection from a common coccidian endoparasite ( Isospora spp.) when feeders were left uncleaned and that daily cleaning (with diluted bleach solution) over a 5-week period successfully decreased parasite burden. Moreover, this pattern in rural finches was true for males but not females. These experimental results reveal habitat- and sex-specific harmful effects of bird feeder use (i.e. when uncleaned in rural areas). Our study is the first to directly indicate to humans who maintain feeders for granivorous birds that routine cleaning can be critical for ensuring the health and viability of visiting avian species. 

Carotenoid pigments serve many endogenous functions in organisms, but some of the more fascinating are the external displays of carotenoids in the colorful red, orange and yellow plumages of birds. Since Darwin, biologists have been curious about the selective advantages (e.g., mate attraction) of having such ornate features, and, more recently, advances in biochemical methods have permitted researchers to explore the composition and characteristics of carotenoid pigments in feathers. Here we review contemporary methods for extracting and analyzing carotenoids in bird feathers, with special attention to the difficulties of removal from the feather keratin matrix, the possibility of feather carotenoid esterification and the strengths and challenges of different analytical methods like high-performance liquid chromatography and Raman spectroscopy. We also add an experimental test of current common extraction methods (e.g., mechanical, thermochemical) and find significant differences in the recovery of specific classes of carotenoids, suggesting that no single approach is best for all pigment or feather types. 

Abstract Quantifying variation in the ability to fight infection among free-living hosts is challenging and often constrained to one or a few measures of immune activity. While such measures are typically taken to reflect host resistance, they can also be shaped by pathogen effects, for example, if more virulent strains trigger more robust immune responses. Here, we test the extent to which pathogen-specific antibody levels, a commonly used measure of immunocompetence, reflect variation in host resistance versus pathogen virulence, and whether these antibodies effectively clear infection. House finches ( Haemorhous mexicanus ) from resistant and susceptible populations were inoculated with > 50 isolates of their novel Mycoplasma gallisepticum pathogen collected over a 20-year period during which virulence increased. Serum antibody levels were higher in finches from resistant populations and increased with year of pathogen sampling. Higher antibody levels, however, did not subsequently give rise to greater reductions in pathogen load. Our results show that antibody responses can be shaped by levels of host resistance and pathogen virulence, and do not necessarily signal immune clearance ability. While the generality of this novel finding remains unclear, particularly outside of mycoplasmas, it cautions against using antibody levels as implicit proxies for immunocompetence and/or host resistance. 

To avoid predation, many animals mimic behaviours and/or coloration of dangerous prey. Here we examine potential sex-specific mimicry in the jumping spider Habronattus pyrrithrix . Previous work proposed that males' conspicuous dorsal coloration paired with characteristic leg-waving (i.e. false antennation) imperfectly mimics hymenopteran insects (e.g. wasps and bees), affording protection to males during mate-searching and courtship. By contrast, less active females are cryptic and display less leg-waving. Here we test the hypothesis that sexually dimorphic dorsal colour patterns in H. pyrrithrix are most effective when paired with sex-specific behaviours. We manipulated spider dorsal coloration with makeup to model the opposite sex and exposed them to a larger salticid predator ( Phidippus californicus ). We predicted that males painted like females should suffer higher predation rates than sham-control males. Likewise, females painted like males should suffer higher predation rates than sham-control females. Contrary to expectations, spiders with male-like coloration were attacked more than those with female-like coloration, regardless of their actual sex. Moreover, males were more likely to be captured, and were captured sooner, than females (regardless of colour pattern). With these unexpected negative results, we discuss alternative functional hypotheses for H. pyrrithrix colours, as well as the evolution of defensive coloration generally. 

Rapid climate change across the globe is having dramatic effects on wildlife. Responses of organisms to shifting thermal conditions often include physiological and behavioural accommodations, but to date these have been largely viewed and studied as naturally evolved phenomena (e.g. heat avoidance, sweating, panting) and not necessarily as strategies where animals exploit other anthropogenic conditions or resources. Moreover, the degree to which native versus introduced species show thermal plasticity has generated much conservation and ecological interest. We previously have observed introduced rosy-faced lovebirds ( Agapornis roseicollis ) perching in the relief-air vents on building faces in the Phoenix, Arizona, USA, metropolitan area, but doing so only during summer. Here, we show that such vent-perching events are significantly associated with extreme outdoor summer temperatures (when daily local highs routinely exceed 40°C). In fact, the temperature threshold at which we detected lovebirds starting to perch in cool air vents mirrors the upper range of the thermoneutral zone for this species. These results implicate novel, facultative use of an anthropogenic resource—industrial air-conditioning systems—by a recently introduced species (within the last 35 years) to cool down and survive extremely hot conditions in this urban ‘heat-island' environment.