Uropygial Secretion Research Articles

Volatiles of symbiotic bacterial origin explain ectoparasitism and fledging success of hoopoes

BackgroundSome parasites use olfactory cues to detect their hosts and, since bacterial symbionts are partially responsible for animal odours, they could influence host parasitism. By autoclaving nest materials of hoopoe (Upupa epops) nests before reproduction started, we explored the hypothetical links between host-associated bacteria, volatiles and parasitism. During the nestling stage, we (i) estimated the level of ectoparasitism by chewing lice (Suborder Mallophaga) in adult hoopoe females and by Carnus haemapterus flies in nestlings, and (ii) characterized microbial communities and volatile profiles of nest environments (nest material and nest cavity, respectively) and uropygial secretions.ResultsExperimental nests had less diverse bacterial communities and more diverse volatile profiles than control nests, while occupants experienced lower intensity of parasitism in experimental than in control nests. The experiment also affected beta diversity of the microbial communities of nest material and of the volatiles of the nestling uropygial secretions. Moreover, microbial communities of uropygial secretions and of nest materials covaried with their volatile profiles, while the volatile profile of the bird secretions explained nest volatile profile. Finally, a subset of the volatiles and bacteria detected in the nest material and uropygial secretions were associated with the ectoparasitism intensity of both adult females and nestlings, and with fledging success.ConclusionsThese results show that a component of animal odours is linked with the microbial communities of the host and its reproductive environment, and emphasize that the associations between bacteria, ectoparasitism and reproductive success are partially mediated by volatiles of bacterial origin. Future work should focus on mechanisms underlying the detected patterns.

Predation attempts on Hoopoe <i>Upupa epops</i> nests in a rural Mediterranean area of central Italy

Seventeen predation attempts on four Hoopoe Upupa epops nests in an heterogenous agricultural Mediterranean area of central Italy were recorded during breeding seasons 2020-21. Camera traps identified 7 different predators’ species, mainly Western whip snake Hierophis viridiflavus and Black rat Rattus rattus. Uropygial secretions and hissing calls from chicks and incubating female inside the breeding cavity always saved the clutches, while no active defense was performed by parents if outside the nest.

Chemical aposematism: the potential for non‐host odours in avian defence

Many birds display plumage coloration and patterns that act as visual aposematic and mimetic signals for predators. Avian aposematism can also be communicated via chemical cues, where so‐called non‐host odours (NHO) emitted from the plumage, the uropygial (preen) gland or other chemical sources denote the status of birds as dangerous or unprofitable hosts for ectoparasitic and haematophagous arthropods. Avian NHO are aposematic signals that in natural concentrations repel nuisance arthropods or inhibit their attraction to hosts, as opposed to being generally unpalatable or toxic to predators. Birds that emit NHO preempt encounters with nuisance arthropods and the pathogens they transmit. Nuisance arthropods that respond to NHO avoid birds that exhibit disabling behavioural, anatomical, physiological and/or chemical defences. As with distinctive plumage patterns that evolved as visual warnings to predators, birds are selected to advertise their non‐host status to nuisance arthropods via distinctive semiochemicals. Short‐chain (C6–C10) aldehydes emitted from the plumage of some birds may act as NHO against a variety of nuisance arthropods. In some birds, the size of the uropygial gland (and presumably its secretory output) is negatively correlated with the degree of ectoparasite infestation or the incidence of malarial infection, thus implicating uropygial secretions in defence against dipteran vectors of haemosporidian pathogens. A field experiment demonstrates that volatiles emanating from the uropygial gland of the Eurasian Hoopoe Upupa epops deter some biting flies. Birds' risky habit of plucking hair from live mammals and incorporating the stolen hair tufts into their nests is hypothesized to serve as a mechanism of appropriating NHO from mammalian skin secretions for nest defence against arthropods. Feathers plucked from heterospecifics and shed snake skins that are incorporated into nests also may emit NHO. Behavioural assays measuring the repellence or attraction‐inhibition of arthropods are needed to elucidate avian NHO. Experimental efforts to elucidate the underlying defences that support avian NHO entail challenges that include the enactment of defences that are variously effective against different arthropods, and the emission of chemical signals that are variously ‘understood’, i.e. avoided, by different arthropods.

Stimuli Followed by Avian Malaria Vectors in Host-Seeking Behaviour.

Simple SummaryVector-borne diseases (VBDs) (e.g., malaria, yellow fever, dengue fever) account for 17% of the estimated global burden of all infectious diseases. They are transmitted to humans and other animals by blood-feeding arthropods. In their pursuit of blood meal, insect vectors use different cues to detect their hosts. The knowledge of these stimuli followed by vectors in this host-seeking behaviour is essential to design strategies to prevent VBD infections. Since its discovery in the late 19th century, avian malaria investigations have allowed significant advances to understand the dynamics and mechanisms of VBD transmission to many organisms, including humans. Here, we review published contributions on the different physical and chemical cues used by mosquitoes and other bird haemosporidian vectors to locate their hosts. This information would be highly valuable for vector surveillance and public health policies.Vector-borne infectious diseases (e.g., malaria, dengue fever, and yellow fever) result from a parasite transmitted to humans and other animals by blood-feeding arthropods. They are major contributors to the global disease burden, as they account for nearly a fifth of all infectious diseases worldwide. The interaction between vectors and their hosts plays a key role driving vector-borne disease transmission. Therefore, identifying factors governing host selection by blood-feeding insects is essential to understand the transmission dynamics of vector-borne diseases. Here, we review published information on the physical and chemical stimuli (acoustic, visual, olfactory, moisture and thermal cues) used by mosquitoes and other haemosporidian vectors to detect their vertebrate hosts. We mainly focus on studies on avian malaria and related haemosporidian parasites since this animal model has historically provided important advances in our understanding on ecological and evolutionary process ruling vector-borne disease dynamics and transmission. We also present relevant studies analysing the capacity of feather and skin symbiotic bacteria in the production of volatile compounds with vector attractant properties. Furthermore, we review the role of uropygial secretions and symbiotic bacteria in bird–insect vector interactions. In addition, we present investigations examining the alterations induced by haemosporidian parasites on their arthropod vector and vertebrate host to enhance parasite transmission. Finally, we propose future lines of research for designing successful vector control strategies and for infectious disease management.

Made-up mouths with preen oil reveal genetic and phenotypic conditions of starling nestlings.

Animal coloration results from pigments, nanostructures, or the cosmetic use of natural products, and plays a central role in social communication. The role of cosmetic coloration has traditionally been focused in scenarios of sexual selection, but it could also take place in other contexts. Here, by using spotless starlings (Sturnus unicolor) as a model system, we explore the possibility that nestlings cosmetically use their intensely yellow-colored uropygial secretion to signal their genetic and/or phenotypic quality. In agreement with the hypothetical cosmetic use of the uropygial secretion, (i) video recorded nestlings collected secretion with the bill at the age of feathering, (ii) cotton swabs turned to the color of secretion after rubbing with them nestlings’ gape, and (iii) gape and skin colorations correlated positively with that of secretion. Furthermore, we found that (iv) secretion coloration has a genetic component, and (v) associated positively with Vitamin E supplementation and (vi) with plasma carotenoid concentration, which highlights the informative value of nestling secretion. Finally, (vii) coloration of begging-related traits and of secretion of nestlings predicted parental feeding preferences. Consequently, all these results strongly suggest that the cosmetic use of colored uropygial secretion might also play a role in parent-offspring communication, complementing or amplifying information provided by the flamboyant colored gapes and skin of nestlings. The use of makeups by offspring for communication with relatives has been scarcely explored and we hope that these results will encourage further investigations in birds and other taxa with parental care.

Dynamics of Bacterial Communities on Eggshells and on Nest Materials During Incubation in the Oriental Tit (Parus minor).

Eggshell bacterial communities may affect hatching success and nestling's condition. Nest materials are in direct contact with the eggshells, but the relationships with the eggshell microbiome during incubation have not been fully elucidated. Here, we characterize eggshell and nest material bacterial communities and their changes during incubation in the Oriental Tit (Parus minor). Bacterial communities on the nest material were relatively stable and remained distinct from the eggshell communities and had higher diversity and greater phylogenetic clustering than the eggshell communities from the same nest, resulting in lower phylogenetic turnover rate of nest material microbiome during incubation than expected by chance. While the species diversity of both communities did not change during incubation, we found significantly greater changes in the structure of bacterial communities on the eggshell than on the nest material. However, eggshell microbiome remained distinct from nest material microbiome, suggesting independent dynamics of the two microbiomes during incubation. We detected an increase in the relative abundance of several bacterial taxa on the eggshell that likely come from the bird's skin, feathers, cloaca/intestine, or uropygial secretion which suggests some exchange of bacteria between the incubating bird and the eggshell. Furthermore, incubation appeared to promote the abundance of antibiotic producing taxa on the eggshell, which may hypothetically inhibit growth of many bacteria including pathogenic ones. Our results suggest that the future studies should focus on simultaneous monitoring of absolute abundance as well as relative abundance in communities on eggshells, nest materials, and the incubating bird's body.

The color of greater flamingo feathers fades when no cosmetics are applied.

Greater flamingos use cosmetic coloration by spreading uropygial secretions pigmented with carotenoids over their feathers, which makes the plumage redder. Because flamingos inhabit open environments that receive direct solar radiation during daytime, and carotenoids bleach when exposed to solar radiation, we expected that the plumage color would fade if there is no maintenance for cosmetic purposes. Here, we show that the concentrations of pigments inside feathers and on the surface of feathers were correlated, as well as that there was a correlation between the concentrations of pigments in the uropygial secretions and on the surface of feathers. There was fading in color (becoming less red) in feathers that received direct solar radiation when there was no plumage maintenance, but not so in others maintained in darkness. When we controlled for the initial color of feathers, the feathers of those individuals with higher concentration of pigments on the feather surfaces were those that lost less coloration after experimental exposure of feathers to sunny conditions. These results indicate that exposure to sunlight is correlated with the fading of feather color, which suggests that individuals need to regularly apply makeup to be more colorful. These results also reinforce the view that these birds use cosmetic coloration as a signal amplifier of plumage color. This may be important in species using highly variable habitats, such as wetlands, since the conditions experienced when molting may differ from those when the signal should be functional, usually months after molting.

Antibacterial and anatomical defenses in an oil contaminated, vulnerable seaduck.

Oil spills have killed thousands of birds during the last 100 years, but nonlethal effects of oil spills on birds remain poorly studied. We measured phenotype characters in 819 eiders Somateria mollissima (279 whole birds and 540 wings) of which 13.6% were oiled. We tested the hypotheses that (a) the morphology of eiders does not change due to oil contamination; (b) the anatomy of organs reflects the physiological reaction to contamination, for example, increase in metabolic demand, increase in food intake, and counteracting toxic effects of oil; (c) large locomotion apparatus that facilitates locomotion increases the risk of getting oiled; and (d) individual eiders with a higher production of secretions from the uropygial grand were more likely to have oil on their plumage. We tested whether 19 characters differed between oiled and nonoiled individuals, showing a consistent pattern. The final model retained seven predictor variables showing relationships between eiders contaminated with oil and food consumption, flight, and diving abilities. We tested whether these effects were due to differences in body condition, liver mass, empty gizzard mass, or other characters that could have been affected by impaired flight and diving ability. There was no evidence of such negative impact of oiling on eiders. We found that significant exposure to oil was associated with increased diversity of antibacterial defense. Oiled eiders did not constitute a random sample, and superior diving ability as reflected by large foot area was at a selective disadvantage during oil spills. Thus, specific characteristics predispose eiders to oiling, with an adaptation to swimming, diving, and flying being traded against the costs of oiling. In contrast, individuals with a high degree of physiological plasticity may experience an advantage because their uropygial secretions counteract the effects of oil contamination.

Sex and age, but not blood parasite infection nor habitat, affect the composition of the uropygial gland secretions in European blackbirds

The uropygial gland of birds produces an oily secretion with different functions, mainly related to plumage protection. In addition, the volatile compounds of this secretion may act as chemical signals that provide information to conspecifics, but it is also possible that those compounds may further attract hematophagous insect vectors such as those responsible for avian malaria transmission. Individual characteristics such as sex and age are usually associated with variation in the composition of the uropygial secretion. Different studies have shown that mosquitoes are more attracted towards birds infected by avian malaria parasites. However, whether the individual infection status by these parasites may lead to differences in the composition of this secretion remains poorly known. We used gas chromatography–mass spectrometry (GC–MS) to characterise the chemical composition of the volatile lipophilic fraction of the uropygial gland secretions of wild European blackbirds and compare its composition in an urban and a forest locality according to their age, sex and infection status by blood parasites. We found differences in the composition of the secretion between age classes and also between sexes within adult birds. However, no differences were found in the chemical composition of the uropygial gland secretion of birds according to their infection status by blood‐parasites and habitat type. These results suggest that haemosporidian infection does not alter the composition of the volatile fraction of uropygial gland secretions in infected birds.

Biochemical and morphological features of the uropygial gland of the Chilean Flamingo and their functional implications

Flamingos inhabit specialized habitats and breed in large colonies, building their nests on islands that limit the access of terrestrial predators. Many aspects of their uropygial gland are still unknown. The uropygial gland, a sebaceous organ exclusive to birds, shares some histological features among species such as the presence of a capsule, adenomers with stratified epithelium and secondary and primary chambers. We found that the uropygial gland of the Chilean Flamingo (Phoenicopterus chilensis) displays most of these characteristics but lacks a primary storage chamber. This absence may be an adaptation to their aquatic environment. The uropygial secretion of this species has a variety of glycoconjugates while its lipid moiety is largely dominated by waxes and minor amounts of triacylglycerols and fatty acids. Mass spectrometry analysis of the preen wax showed branched fatty acids of varied chain length and unbranched fatty alcohols, resulting in a complex mixture of wax esters and no differences between sexes were observed. The glycoconjugates present in the preen secretion could play a role as antimicrobial molecules, as suggested for other bird species, while the absence of diester waxes in flamingos might be related with their nesting habits and limited exposure to predation. Our results were evaluated according to physiological and ecological aspects of the flamingo’s biology.

Cosmetic coloration of cross-fostered eggs affects paternal investment in the hoopoe (Upupa epops).

The signalling hypothesis suggests that avian eggshell coloration is a sexually selected female signal advertising her quality to its male partner, thereby stimulating his provisioning rate. This hypothesis has been tested for structural eggshell pigments, but not for cosmetic colorations, such as that produced by the uropygial secretion on eggshells. During the breeding season, female hoopoes (Upupa epops) host in their uropygial glands symbiotic bacteria. Females actively smear the eggshells with their secretion, protecting embryos from pathogenic trans-shell infections and changing eggshell coloration. Because the colour of the secretions is related to their antimicrobial potential, cosmetic eggshell coloration may act as a cue or even as a post-mating sexually selected signal if it affects male provisioning rates. To experimentally test this hypothesis, we cross-fostered already-smeared clutches between hoopoe nests, and quantified male feeding behaviour to females before and after the experiment. This approach allows disentanglement of the effects of female quality and of egg coloration on male investment. In accordance with the hypothesis, males adjusted their provisioning rate to the eggshell cosmetic coloration. This is, to our knowledge, the first experimental demonstration that egg colour stained with uropygial secretion could act as a post-mating sexual signal of female quality to males.

The uropygial gland microbiome of house sparrows with malaria infection

Birds secrete preen oil from the uropygial (preen) gland which is used to maintain feather integrity and communicate through odour. The uropygial secretion is believed to influence host attractiveness to biting insects, thereby altering the risk of infection by vector‐transmitted blood parasites. Previous studies have documented a presence of bacteria in the uropygial secretion; however, the microbial community in the gland is still largely unknown. In addition, we have no information yet as to whether there are any associations between these uropygial gland microbes and haemosporidian parasite infection. Here, we characterise the microbiome of the uropygial gland secretion in 23 wild‐caught house sparrows Passer domesticus from Peru and investigate whether individuals with natural malaria Plasmodium infection have different preen oil microbiota than uninfected birds. We found no differences in microbial alpha diversity or richness, and malaria infection explained approximately 5% of the overall microbiome composition, however, this was not statistically significant. On the other hand, birds with malaria infection had significantly higher abundances of bacteria from the genera Arthrobacter and Micrococcus in their gland, whereas uninfected birds harboured higher abundances of Rhodococcus, Phenylobacterium and Enhydrobacter. These first results of the uropygial gland microbiome in malaria‐infected birds illustrate the presence of a more specific relationship between certain members of the gland microbiota and Plasmodium parasites in birds, which opens up new questions on the role of the uropygial gland in avian health.

Female-Based Patterns and Social Function in Avian Chemical Communication.

Much of the growing interest in avian chemical signals has focused on the role of kin recognition or mate attraction, often with an emphasis on males, with uropygial gland secretions perhaps providing information about an individual's identity and quality. Yet, data collected to date suggest sexual dimorphism in uropygial glands and secretions are often emphasized in female, rather than in male birds. That is, when a sexual difference occurs (often during the breeding season only), it is the female that typically exhibits one of three patterns: (1) a larger uropygial gland, (2) a greater abundance of volatile or semi-volatile preen oil compounds and/or (3) greater diversity of preen oil compounds or associated microbes. These patterns fit a majority of birds studied to date (23 of 30 chemically dimorphic species exhibit a female emphasis). Multiple species that do not fit are confounded by a lack of data for seasonal effects or proper quantitative measures of chemical compounds. We propose several social functions for these secretions in female-based patterns, similar to those reported in mammals, but which are largely unstudied in birds. These include: (1) intersexual advertisement of female receptivity or quality, including priming effects on male physiology, (2) intrasexual competition, including scent marking and reproductive suppression or (3) parental behaviors, such as parent-offspring recognition and chemical protection of eggs and nestlings. Revisiting the gaps of chemical studies to quantify the existence of female social chemosignals and any fitness benefit(s) during breeding are potentially fruitful but overlooked areas of future research.

Comparative morphology and histochemistry of the uropygial gland of the endangered and endemic Hooded Grebe (Podiceps gallardoi, Podicipediformes)

AbstractThe Hooded Grebe is an endangered and endemic species of Podicipediformes of Argentina. Many aspects of this bird's biology are still unknown including the uropygial gland. This is the first morphological and histochemical description of the uropygial gland for this species in a comparative context. The uropygial gland of these birds had parallel arranged lobes with a kidney‐like shape, a conical papilla and a feather tuft in a sub‐terminal position. The lobes were composed of tubular adenomers with a straight course that lead to secondary chambers. The capsule and connective tissue around the adenomers had elastic fibres. It showed a positive reaction to AlcianBlue/Periodic Acid Schiff and several lectins indicating the presence of glycoconjugates. The uropygial gland of the Hooded Grebe shares morphological characteristics with other aquatic species (e.g. secondary chambers) and the presence of glycoconjugates might suggest protective functions against microbes as previously proposed. The sub‐terminal position of the feather tuft is a unique characteristic of this species indicating that this position leaves the tuft in a dorsal location and could be involved in parent‐chick recognition mediated by odour transmission. Further studies are needed to increase our knowledge on some behavioural aspects of this species related to the biochemical composition of the uropygial secretion.

Effects of Chemical and Auditory Cues of Hoopoes (Upupa epops) in Repellence and Attraction of Blood-Feeding Flies

Research on the mechanisms involved in host location by parasites is of paramount importance and may aid in developing protective measures against them. This topic attains far-reaching repercussions for human and animal welfare regarding parasites transmitting vector-borne pathogens, such as blood-feeding flies. Very few studies have evaluated the effect of bird-derived cues on attraction of vectors in field conditions. We here explored the attraction of different groups of blood-feeding flies (mosquitoes, blackflies and biting midges) to auditory cues produced by begging hoopoe (Upupa epops) nestlings, and to three chemical cues derived from hoopoe nestlings or nests (uropygial secretion, symbiotic bacteria isolated from the secretion, and nest material) in the field. We deployed insect traps baited with the different stimuli at the beginning and at the end of the hoopoe breeding-season in four different habitats. Abundance of blood-feeding flies varied depending on habitat and sampling period. Begging auditory cues of nestling hoopoes did not affect abundance of flies. However, chemical stimuli affected abundance of mosquitoes, which were less abundant in traps baited with bacteria or with nest material than in control traps. Abundance of biting midges in traps also depended on the chemical stimulus but in interaction with sampling period or habitat. Fewer biting midges were collected in traps baited with bacteria and with secretion in the habitats where abundance of biting midges is higher. Our results suggest that uropygial secretion of hoopoes, and symbiotic bacteria living in this secretion, may repel blood-feeding flies from their nests.

Single fluff-spray application of mother hen uropygial secretion analogue positively influences bursa of Fabricius development and the heterophil-to-lymphocyte ratio in ROSS 308 chicks

Stress is an important cause of illness and mortality in chick production. Stressors such as manipulation, absence of maternal care, transport, and housing can lead to welfare issues, immunodepression, and decreased productivity. The mother hen uropygial secretion analogue (MHUSA), a synthetic analog of a maternal semiochemical secretion, has been proven to protect chicks and broilers against stress, significantly reducing the heterophil-to-lymphocyte ratio. The aim of the present study was to test the effects of the MHUSA on chicks' stress when single-sprayed on their fluff at the age of 1 d. Two-hundred eighty ROSS 308 chicks were included in the study. At day 1, each chick received a spray of 200 μL of a 2% MHUSA aqueous solution (140 chicks) or the same amount of the excipient (control group, 140 chicks), and then chicks were housed in 2 separate rooms. To assess the persistence of the MHUSA after this single application, fluff was sampled from 10 chicks every day for 7 d and at day 13 and 19, weighed, placed in dichloromethane, and analyzed by gas chromatography. Blood smears and the bursa of Fabricius were collected every 3 d from 10 chicks of each group for 36 d to assess the heterophil-to-lymphocyte ratio and the bursa weight–to–BW ratio, respectively. Gas chromatography analysis showed that the MHUSA was present on chick fluff until day 5. The statistical analysis revealed that the heterophil-to-lymphocyte ratio was lower in the MHUSA group at day 4, 7, and 9 (P < 0.0001 for day 4 and 7; P = 0.0377 for day 9). The bursa weight–to–BW ratio was significantly higher in the MHUSA group than in the control group from day 4 until day 29. These results confirm the beneficial effects of the MHUSA on chicks' adaptation to the new environment and on bursa of Fabricius development, suggesting its potential role in improving chicks' immune response.

Hoopoe Upupa epops male feeding effort is related to female cosmetic egg colouration

Avian eggshell colouration might function as a post‐mating sexually selected signal of female quality, influencing male parental investment and, hence, reproductive success. This hypothesis has been tested for intrinsic eggshell pigments as biliverdin (blue‐green colouration) and/or protoporphyrin (brown coloured spots), but never for colourations applied post‐laying. Post‐laying staining colouration due to, for instance, uropygial secretion of the female could reflect its phenotypic properties and, thus, might be a cue for male investment in reproduction. In hoopoes, the uropygial gland of incubating females hosts symbiotic bacteria that are responsible for the brown colour of their uropygial secretion and of the eggshells, as they cover their bluish‐grey eggshells with gland secretion after laying. The secretion protects embryos from pathogenic trans‐shell infections and, thus, egg colouration may function as a cue or even as a post‐mating sexually selected signal of antimicrobial potential in hoopoes. In a wild hoopoe population breeding in nest boxes in Spain, we test this hypothesis by exploring whether egg colour predicts male parental investment. In accordance with the hypothesis, we found that the amount of food provided by males to incubating females was higher in nests with less saturated eggshell colours. This relationship was affected by female body condition. High quality females in terms of body condition and/or in secretion colour obtained better males in terms of provisioning effort during incubation. Given that eggshell saturation is negatively related to density of bacterial symbionts in uropygial secretions, one possibility is that males may regulate their parental investment in accordance to the expected characteristics of mutualistic bacteria hosted in uropygial glands and deposited on eggshells. We discuss alternative explanations for our results, concluding that the post‐mating sexual selection hypothesis is the most likely but experimental modification of egg colour is needed to test it further.

Mosquitoes are attracted by the odour of Plasmodium-infected birds

Parasites can manipulate their hosts to increase their transmission success. Avian malaria parasites (Plasmodium) are thought to alter the cues such as host odour, used by host-seeking mosquitoes. Bird odour is affected by secretions from the uropygial gland and may play a role in modulating vector-host interactions. We tested the hypothesis that mosquitoes are more attracted to the uropygial secretions and/or whole-body odour (headspace) of Plasmodium-infected house sparrows (Passer domesticus) than to those of uninfected birds. We tested the attraction of nulliparous (e.g. uninfected mosquitoes without previous access to blood) Culex pipiens females towards these stimuli in a dual-choice olfactometer. We used Gas Chromatography-Mass Spectrometry (GC–MS) analyses to assess whether Plasmodium infection is associated with differences in the chemical composition of uropygial secretions. Mosquitoes were more attracted to the odours of infected than uninfected birds, regardless of sex. However, the significant interaction between infection status and the stimuli (uropygial secretion or headspace) showed that mosquitoes were more attracted to the headspace of infected birds; no differences were found in the case of uropygial secretions. The compounds in the volatile lipophilic fraction of the uropygial secretion did not differ between infected and uninfected birds. These results support the host manipulation hypothesis since avian Plasmodium parasites may be capable of altering their host’s body odour, thereby making infected individuals more attractive to mosquitoes.

Experimental old nest material predicts hoopoe Upupa epops eggshell and uropygial gland microbiota

Nest re‐use in birds has the potential cost of infection by parasites and pathogens but may also be a source of beneficial symbiotic bacteria transmitted horizontally. Eurasian hoopoes Upupa epops host antibiotic‐producing bacteria in their uropygial gland but only while breeding, which suggests that the nest‐hole may be a source of those symbionts. Interestingly, hoopoes do not build nests, thus might prefer for reproduction nest holes with soft materials from previous reproductions. Here, we tested experimentally this preference by installing in the field new nest boxes that were left empty or filled with either sawdust or a mixture of sawdust and hoopoe's nest material from the previous year. We explored the experimental effect on the composition of the uropygial secretion bacterial community, on eggshell bacterial loads, and on several proxies of reproductive success. Hoopoes bred significantly more often in nest boxes with nest material than in empty ones, but the type of nest material did not affect nest box occupancy. Eggs in nest boxes with old‐soft material harbored higher bacterial density on their shells, and the microbiota of the uropygial secretion of nestlings and females in these nest boxes differed from those in nest boxes without old‐soft material. Moreover, although the experiment did not affect breeding success or related proxies, several operational taxonomic units from female uropygial secretions were positively associated with hatching success. This is the first experimental evidence showing that re‐used nest material affects the bacterial community of the uropygial secretions of hoopoe females. This suggests that the nest material can be a source of strains for their incorporation to both the uropygial gland and eggshell communities, highlighting a possible advantage of nest re‐use previously unconsidered.

House sparrow uropygial gland secretions do not attract ornithophilic nor mammophilic mosquitoes.

Mosquito feeding preferences determine host-vector contact rates and represent a key factor in the transmission of vector-borne pathogens. The semiochemical compounds of which vertebrate odours are composed probably play a role in mosquito host choice. Birds spread secretions from uropygial gland over their feathers to protect their plumage, comprising behaviour that may in turn affect odour profiles. Although uropygial secretions are expected to modify the attractiveness of birds to mosquitoes, contradictory findings have been reported. Mosquito species differ in their feeding preferences, with some species feeding mainly on birds (ornithophilic species) and others on mammals (mammophilic species). Consequently, it is possible that ornithophilic and mammophilic species differ in their response to uropygial gland secretions. Using a dual-choice olfactometer, the present study tests this hypothesis by comparing the behavioural response to uropygial gland secretions from juvenile male and female house sparrows (Passer domesticus) in the ornithophilic Culex pipiens and the mammophilic Aedes (Ochlerotatus) caspius mosquitoes. No differences were found in the response of either mosquito species to the uropygial gland secretions. Therefore, the preference of ornithophilic mosquitoes for avian hosts is apparently not explained by a greater attraction of mosquitoes to the uropygial gland secretion odour when presented in combination with a CO2 -enriched airflow.