Innate and adaptive immune proteins in the preen gland secretions of male house sparrows

Recent studies have demonstrated that preen oil acts to reduce or eliminate feather-associated bacteria. The mechanisms underlying this antibacterial activity, however, are incompletely understood. In addition to the activity of alcohols (i.e. 3,7-dimethyloctan-1-ol), recent research has suggested that antimicrobial peptides may underlie the antibacterial activity of preen oil. Here, we document the presence of innate and adaptive immune proteins, lysozyme and immunoglobulin Y (IgY), in the preen oil of house sparrows Passer domesticus. We suggest lysozyme functions as an antimicrobial agent, with potentially important impacts against Gram-positive feather degrading bacteria. Furthermore, both lysozyme and IgY likely act in local immune defence of the preen gland, and may also play a role in regulating the local microbiome, with potentially important consequences for chemical communication and signalling. Our findings suggest that the preen gland and its secretions should be considered an integral part of the body's first line of defence against invading infections.     

Preen oil and bird fitness: a critical review of the evidence

The uropygial gland is a holocrine complex exclusive to birds that produces an oleaginous secretion (preen oil) whose function is still debated. Herein, I examine critically the evidence for the many hypotheses of potential functions of this gland. The main conclusion is that our understanding of this gland is still in its infancy. Even for functions that are considered valid by most researchers, real evidence is scarce. Although it seems clear that preen oil contributes to plumage maintenance, we do not know whether this is due to a role in reducing mechanical abrasion or in reducing feather degradation by keratinophilic organisms. Evidence for a function against pathogenic bacteria is mixed, as preen oil has been demonstrated to act against bacteria in vitro, but not in vivo. Nor is it clear whether preen oil can combat pathogenic bacteria on eggshells to improve hatching success. Studies on the effect of preen oil against dermatophytes are very scarce and there is no evidence of a function against chewing lice. It seems clear, however, that preen oil improves waterproofing, but it is unclear whether this acts by creating a hydrophobic layer or simply by improving plumage structure. Several hypotheses proposed for the function of preen oil have been poorly studied, such as reduction of drag in flight. Similarly, we do not know whether preen oil functions as repellent against predators or parasites, makes birds unpalatable, or functions to camouflage birds with ambient odours. On the other hand, a growing body of work shows the important implications of volatiles in preen oil with regard to social communication in birds. Moreover, preen oil clearly alters plumage colouration. Finally, studies examining the impact of preen oil on fitness are lacking, and the costs or limitations of preen‐oil production also remain poorly known. The uropygial gland appears to have several non‐mutually exclusive functions in birds, and thus is likely to be subject to several selective pressures. Therefore, future studies should consider how the inevitable trade‐offs among different functions drive the evolution of uropygial gland secretions.     

Astaxanthin is responsible for the pink plumage flush in Franklin's and Ring-billed gulls

ABSTRACT.   Carotenoid pigments produce the red, orange, and yellow plumage of many birds. Carotenoid-containing feathers are typically rich in color and displayed by all adult members of the species. In many gulls and terns, however, an unusual light pink coloring (or flush) to the normally white plumage can be found in highly variable proportions within and across populations. The carotenoid basis of plumage flush was determined in an Elegant Tern ( Sterna elegans ; Hudon and Brush 1990 ), but it is not clear if all larids use this same mechanism for pink plumage coloration. We examined the carotenoid content of pink feathers in Franklin's ( Larus pipixcan ) and Ring-billed ( Larus delawarensis ) gulls and found that a single carotenoid—astaxanthin—was present. Astaxanthin was primarily responsible for the flush in Elegant Terns as well, but was accompanied by other carotenoids (e.g., canthaxanthin and zeaxanthin), as is typical of most astaxanthin-containing bird feathers. In both gull and tern species, carotenoids were contained within feathers and did not occur on the plumage surface in preen oil, as some have previously speculated. We hypothesize that some gulls turn pink because they acquire unusually high amounts of astaxanthin in their diets at the time of feather growth. It is tempting to link the increase in sightings of pink Ring-billed Gulls since the late 1990s with the introduction of pure, synthetic astaxanthin to the diets of hatchery-raised salmon.     

Plumage reflectance is not affected by preen wax composition in red knots Calidris canutus

It has recently been shown that sandpipers (Scolopacidae) abruptly switch the chemical composition of their preen gland secretions from mono- to diester waxes just before the period of courtship. The timing and context of the shift suggested that diesters could provide a visible quality signal during mate choice. We used captive red knots Calidris canutus to test whether mono- and diester preen waxes affect the light reflectance ("colour") of the plumage. We also determined light absorbance spectra of the two wax types. The reflectance of breast feathers of the breeding plumage was measured with spectrophotometry when birds secreted monoesters and six weeks later when they secreted diester preen waxes. Light reflectance was also measured after removing the mono- and diester waxes from the plumage with a solvent. The results show that: (1) diester preen waxes absorb more light, especially ultraviolet (UV), than monoester preen waxes, but that (2) the compositional shift in the preen waxes did not change plumage reflectance and, (3) the removal of preen waxes did not change the reflectance of the plumage within the light spectrum assumed visible to birds (320–700 nm). This is not consistent with the idea that compositional shifts in the preen waxes of red knots have a visual function.     

Use of TLC‐FID and GC‐MS/FID to examine the effects of migratory state,diet and captivity on preen wax composition in White‐throated Sparrows Zonotrichia albicollis

Preen wax is important for plumage maintenance and other functions. Its chemical composition is complex, and separating and quantifying its components, commonly by gas chromatography (GC), can be challenging. We present a simple analytical system consisting of thin‐layer chromatography/flame ionization detection (TLC‐FID) using a solvent system of 100% toluene to analyse the complex compound classes present in preen wax. We used GC and TLC‐FID to investigate the effects of migratory status, diet and captivity on the preen wax composition of White‐throated Sparrows Zonotrichia albicollis, and to measure the quantity of preen wax on the head, primary and tail feathers. White‐throated Sparrows produced preen wax containing only monoesters regardless of migratory state. The monoesters contained several isomers consisting of homologous series of fatty alcohols (C10–C20) and fatty acids (C13–C19) esterified together in different combinations to form monoesters with total carbon numbers ranging from C23 to C38. Weighted average monoester carbon number was greater in captive birds than in wild birds and was greater in captives fed a formulated diet enriched with sesame oil than in birds fed the same diet enriched with fish oil. Captivity and migratory state also affected the complexity of the mixture of monoesters. There was significantly more preen wax on head feathers compared with primary and tail feathers. We suggest that among its many functions, preen wax may play a role in drag reduction by affecting the physical properties of feathers, and/or the fluid flow at their surfaces.     

Body‐mass‐dependent trade‐off between immune response and uropygial gland size in house sparrows Passer domesticus

Parasites greatly impact host fitness. The immune system is fundamental to combat endoparasites, and survival increases with greater investment in immunity. Some ectoparasites, by contrast, are reportedly combated by the use of the uropygial gland, an organ exclusive to birds, which secretes an oily substance (preen oil) that is spread on plumage. However, both mounting an immune response against a parasite and producing uropygial gland secretion depend on the same resources, a situation which may induce trade‐offs between the two antiparasitic functions. In this study, I experimentally test whether immune response is traded off against uropygial gland size in the house sparrow Passer domesticus. In the experiment, a group of sparrows were injected with an antigen (lipopolysaccharide, LPS), which stimulates the immune system, while the other group received a sham injection. The uropygial gland of LPS‐treated birds decreased significantly more than that of the control birds after treatment. Nevertheless, the effect of the treatment was limited to house sparrows with low body mass, suggesting that heavy house sparrows were able to produce an immune response while maintaining a relatively large uropygial gland. Given that uropygial gland size is strongly related to production of preen oil, these results suggest that preen oil production declines in birds in poor body condition when resources are preferentially diverted to other demanding functions, such as the immune system. Considering that the uropygial gland is involved in several fitness‐related processes in birds, the trade‐off between immune response and uropygial gland size may have important consequences for bird life histories.     

Characterization of antimicrobial substances produced by Enterococcus faecalis MRR 10-3, isolated from the uropygial gland of the hoopoe (Upupa epops)

The uropygial gland (preen gland) is a holocrine secretory gland situated at the base of the tail in birds which produces a hydrophobic fatty secretion. In certain birds, such as the hoopoe, Upupa epops, the composition of this secretion is influenced by both seasonal and sexual factors, becoming darker and more malodorous in females and in their nestlings during the nesting phase. The secretion is spread throughout the plumage when the bird preens itself, leaving its feathers flexible and waterproof. It is also thought to play a role in defending the bird against predators and parasites. We have isolated from the uropygial secretion of a nestling a bacterium that grows in monospecific culture which we have identified unambiguously by phenotypic and genotypic means as Enterococcus faecalis. The strain in question produces antibacterial substances that are active against all gram-positive bacteria assayed and also against some gram-negative strains. Its peptide nature identifies it as a bacteriocin within the group known as enterocins. Two peptides were purified to homogeneity (MR10A and MR10B), and matrix-assisted laser desorption ionization-time of flight (mass spectrometry) analysis showed masses of 5201.58 and 5207.7 Da, respectively. Amino acid sequencing of both peptides revealed high similarity with enterocin L50A and L50B (L. M. Cintas, P. Casaus, H. Holo, P. E. Hernández, I. F. Nes, and L. S. H?varstein, J. Bacteriol. 180:1988-1994, 1998). PCR amplification of total DNA from strain MRR10-3 with primers for the L50A/B structural genes and sequencing of the amplified fragment revealed almost identical sequences, except for a single conservative change in residue 38 (Glu-->Asp) in MR10A and two changes in residues 9 (Thr-->Ala) and 15 (Leu-->Phe) in MR10B. This is the first time that the production of bacteriocins by a bacterium isolated from the uropygial gland has been described. The production of these broad-spectrum antibacterial substances by an enterococcal strain living in the uropygial gland may be important to the hygiene of the nest and thus to the health of the eggs and chicks.     

Eggshell Bacterial Load Is Related to Antimicrobial Properties of Feathers Lining Barn Swallow Nests

The use of feathers to line bird’s nests has traditionally been interpreted as having a thermoregulatory function. Feather-degrading bacteria growing on feathers lining nests may have antimicrobial properties, which may provide an additional benefit to lining nests with feathers. We test the hypothesis that the production of antimicrobial substances by feather bacteria affects the microbiological environment of the nest, and therefore the bacterial density on eggshells and, indirectly, hatching success. These effects would be expected to differ between nests lined with pigmented and white feathers, because bacteria grow differently on feathers of different colors. We experimentally manipulated the composition of pigmented and unpigmented feathers in nests of the barn swallow (Hirundo rustica) and studied the antimicrobial properties against the keratin-degrading bacterium Bacillus licheniformis of bacteria isolated from feathers of each color. Analyzed feathers were collected at the end of the incubation period, and antimicrobial activity was defined as the proportion of bacteria from the feathers that produce antibacterial substances effective against B. licheniformis. Our experimental manipulation affected antimicrobial activity, which was higher in nests with only white feathers at the beginning of incubation. Moreover, white feathers showed higher antimicrobial activity than black ones. Interestingly, antimicrobial activity in feathers of one of the colors correlated negatively with bacterial density on feather of the opposite color. Finally, antimicrobial activity of white feathers was negatively related to eggshell bacterial load. These results suggest that antimicrobial properties of feathers in general and of white feathers in particular affect the bacterial environment in nests. This environment in turn affects the bacterial load on eggshells, which may affect hatching success.     

Characterization of Antimicrobial Substances Produced by Enterococcus faecalis MRR 10-3, Isolated from the Uropygial Gland of the Hoopoe (Upupa epops)

The uropygial gland (preen gland) is a holocrine secretory gland situated at the base of the tail in birds which produces a hydrophobic fatty secretion. In certain birds, such as the hoopoe, Upupa epops, the composition of this secretion is influenced by both seasonal and sexual factors, becoming darker and more malodorous in females and in their nestlings during the nesting phase. The secretion is spread throughout the plumage when the bird preens itself, leaving its feathers flexible and waterproof. It is also thought to play a role in defending the bird against predators and parasites. We have isolated from the uropygial secretion of a nestling a bacterium that grows in monospecific culture which we have identified unambiguously by phenotypic and genotypic means as Enterococcus faecalis. The strain in question produces antibacterial substances that are active against all gram-positive bacteria assayed and also against some gram-negative strains. Its peptide nature identifies it as a bacteriocin within the group known as enterocins. Two peptides were purified to homogeneity (MR10A and MR10B), and matrix-assisted laser desorption ionization-time of flight (mass spectrometry) analysis showed masses of 5201.58 and 5207.7 Da, respectively. Amino acid sequencing of both peptides revealed high similarity with enterocin L50A and L50B (L. M. Cintas, P. Casaus, H. Holo, P. E. Hernández, I. F. Nes, and L. S. Håvarstein, J. Bacteriol. 180:1988-1994, 1998). PCR amplification of total DNA from strain MRR10-3 with primers for the L50A/B structural genes and sequencing of the amplified fragment revealed almost identical sequences, except for a single conservative change in residue 38 (Glu→Asp) in MR10A and two changes in residues 9 (Thr→Ala) and 15 (Leu→Phe) in MR10B. This is the first time that the production of bacteriocins by a bacterium isolated from the uropygial gland has been described. The production of these broad-spectrum antibacterial substances by an enterococcal strain living in the uropygial gland may be important to the hygiene of the nest and thus to the health of the eggs and chicks.     

Preen gland function in layer fowls: factors affecting morphology and feather lipid levels

The effects of age and external factors on preen gland morphology and feather lipid concentrations in layer fowl (Gallus domesticus) have not previously been described. This work examines how floor substrate, whether a bird is feather pecked or not, and age influence both gross and histological morphology. Furthermore, the effects of age, beak trimming and floor substrate on feather lipid concentration (mg lipid per g feathers) are investigated. Neither absolute nor relative preen gland weight were reliably affected by floor substrate or feather pecked status. However, these parameters were strongly affected by changes in bird age and related body weight changes. The microstructures of the gland also increased consistently with age. Feather lipid concentration generally increased with age. Feather lipid was strongly influenced by the presence or absence of a dustbathing substrate. Of all the parameters tested here, the age and growth of the bird had the greatest effects on preen gland development. Feather lipid concentration is also influenced by age, and by the presence or absence of a dustbathing substrate.     

Preen waxes do not protect carotenoid plumage from bleaching by sunlight

The plumage coloration of wild birds often changes during the breeding season. One of the possible reasons for this is that sunlight, and particularly ultraviolet (UV) wavelengths, degrades the pigments responsible for plumage coloration. It has been suggested that birds may apply preen wax to feathers to protect feathers from bleaching. This hypothesis is tested by exposing carotenoid-based breast feathers of Great Tits to ambient light, light filtered to exclude UV and darkness. Preen waxes were experimentally removed from feather samples and the effect of light on coloration of treatment and control feathers compared. Ambient light had an effect on feather colour but preen wax did not. Feathers exposed to sun gradually became less saturated and hues shifted towards shorter wavelengths. This was not apparent in control feathers kept in darkness. Feathers exposed to full-spectra sunlight faded more than those that were kept in light with UV wavelengths removed. There was a decrease in brightness of feathers in both experimental and control groups, which was assumed to be an effect of dirt accumulation. This experiment confirmed earlier suspicions regarding the detrimental effects of UV irradiation on carotenoid-based coloration of avian feathers but failed to show any protective function of preen waxes. The possible consequences of these mechanisms of colour change for birds with regard to mating strategies are discussed.     

Variation in the wing-clapping display of Clapper Larks

The pied plumage of the adult Black Sparrowhawk is rather exceptional in the genus Accipiter and it could be explained by functionality or by phylogenetic relationships. The moult pattern of museum specimens is presented, supplementing information from captive birds. The post-juvenile moulting sequence is similar to that of the Northern Goshawk. The moult of primaries starts at, or just after, the beginning of body moult; moult of the secondaries also starts early and progresses from three consecutive foci, and tail moult starts early but is less predictable. A few body feathers and tail feathers may remain in place until the second moult. The pied flank feathers appear at an early stage. Some adult specimens are in arrested annual moult. Two with definite serially-descendant moult were discovered; this is related to the fact that the species is known to be double-brooded. Serially descendant moult was not known in this species and is rarely mentioned in the genus. Possible functions of the pied plumage are discussed: crypsis, mimicry, hunting strategy, and sexual attraction. Its taxanomic status is obscure. Although the streaked juvenile plumage of the Black Sparrowhawk is similar to those of the Northern Goshawk A. gentilis, Meyer's Goshawk A. meyerianus and Henst's Goshawk A. hentsi, adult and juvenile plumages are variable within the genus, and thus are not a reliable indicator of taxanomic relationships.     

Antimicrobial chemicals in hoopoe preen secretions are produced by symbiotic bacteria

Animals frequently use metabolites produced by symbiotic bacteria as agents against pathogens and parasites. Secretions from the preen gland of birds are used for this purpose, although its chemicals apparently are produced by the birds themselves. European hoopoes Upupa epops and green woodhoopoes Phoeniculus purpureus harbour symbiotic bacteria in the uropygial gland that might be partly responsible for the chemical composition of secretions. Here we investigate the antimicrobial activity of the volatile fraction of chemicals in hoopoe preen secretions, and, by means of experimental antibiotic injections, test whether symbiotic bacteria living within the uropygial gland are responsible for their production. Hoopoes produce two different kinds of secretions that differ drastically in their chemical composition. While the malodorous dark secretions produced by nestlings included a complex mix of volatiles, these chemicals did not appear in white secretions produced by non-nesting birds. All volatiles detected showed strong antibacterial activity, and a mixture of the chemicals at the concentrations measured in nestling glands inhibited the growth of all bacterial strains assayed. We found support for the hypothesized role of bacteria in the production of such antimicrobial chemicals because experimental clearance of bacteria from glands of nestlings with antibiotics resulted in secretions without most of the volatiles detected in control individuals. Thus, the presence of symbiotic bacteria in the uropygial gland provides hoopoes with potent antimicrobials for topical use.     

Preservation agents influence UV-coloration of plumage in museum bird skins

Plumage colour has always been a major criterion when describing and distinguishing bird taxa. Today, the use of reflection spectrophotometry is the most commonly used technique to study plumage coloration. A major advantage of this method is the opportunity of observing reflection beyond the human colour vision range—including the UV-waveband. Traditional taxonomic and phylogenetic research is often based on bird skins held in collections in natural history museums worldwide. Different agents for preservation have been used to prevent skins from being damaged by arthropod pests. Sometimes, parts of the plumage have been contaminated with stains from preservation agents. When dried, they are almost invisible to the human eye under normal sunlight conditions and cause no obvious change to feather coloration. However, some preservation agents contain fluorescent components which show up brightly when illuminated with UV-light. Furthermore, undetectable to the human eye, stains from these agents annihilate UV-reflection, preventing accurate data collection based on the UV-reflection of bird feathers. Measuring plumage parts which have been accidentally stained will lead to a relative underestimate of UV-reflection. In studying 20,000 samples, we found fluorescent stains in some 300 bird skins of varying ages (1913–2004) in museum collections throughout Europe and the USA. Different preservation agents have been evaluated for their fluorescence properties.     

Sexually selected male plumage color is testosterone dependent in a tropical passerine bird, the red-backed fairy-wren (Malurus melanocephalus)

Background

Sexual signals, such as bright plumage coloration in passerine birds, reflect individual quality, and testosterone (T) may play a critical role in maintaining signal honesty. Manipulations of T during molt have yielded mixed effects on passerine plumage color, in most cases delaying molt or leading to production of drab plumage. However, the majority of these studies have been conducted on species that undergo a post-nuptial molt when T is low; the role of T in species that acquire breeding plumage during a pre-nuptial molt remains largely unexplored.

Methodology/Principal Findings

We experimentally tested the effects of increased T on plumage color in second-year male red-backed fairy-wrens (Malurus melanocephalus), a species in which after-second-year males undergo a pre-nuptial molt into red/black (carotenoid and melanin-based) plumage and second-year males either assume red/black or brown breeding plumage. T treatment stimulated a rapid and early onset pre-nuptial molt and resulted in red/black plumage acquisition, bill darkening, and growth of the sperm storage organ, but had no effect on body condition or corticosterone concentrations. Control males molted later and assumed brown plumage. T treated males produced feathers with similar but not identical reflectance parameters to those of unmanipulated after-second-year red/black males; while reflectance spectra of red back and black crown feathers were similar, black breast feathers differed in UV chroma, hue and brightness, indicating a potentially age and plumage patch-dependent response to T for melanin- vs. carotenoid-pigmentation.

Conclusions/Significance

We show that testosterone is the primary mechanism functioning during the pre-nuptial molt to regulate intrasexually variable plumage color and breeding phenotype in male red-backed fairy-wrens. Our results suggest that the effects of T on plumage coloration may vary with timing of molt (pre- vs. post-nuptial), and that the role of T in mediating plumage signal production may differ across age classes, plumage patches, and between pigment-types.     

Cosmetic plumage coloration by iron oxides does not confer protection against feather wear

The active acquisition of plumage cosmetic coloration by iron oxides has been described in several bird species (notably the Bearded Vulture Gypaetus barbatus, but also in cranes, pelicans and other vulture species) but its function remains controversial. We tested the hypothesis that iron oxide acquired through mud bathing protects feathers from wear. We experimentally stained 13 breast feathers collected from two White Storks Ciconia ciconia with mud from a ferruginous pond regularly used by Bearded Vultures, while another 13 feathers (controls) were treated with water. All feathers were exposed to a controlled physical abrasion treatment. We found no differences in wear between control and stained feathers, which is counter to predictions of the wear protection hypothesis for the acquisition of this cosmetic plumage coloration.     

Preen oil composition of Pied Flycatchers is similar between partners but differs between sexes and breeding stages

Preen oil, the secretion of the uropygial gland, may be an important source of body odour in birds. By characterizing the chemical composition of preen oil, we can describe the olfactory phenotypes of birds and investigate whether odours could have a function in sexual signalling or other chemical communication. Here we analysed the preen oil of a wild passerine, the European Pied Flycatcher Ficedula hypoleuca, to find out whether it holds socially relevant information. We sampled both the female and male of breeding pairs during nestling rearing to test for sex differences and within-pair similarity. We additionally sampled the females during incubation to test for changes across breeding stages and for individual repeatability of chemical profiles. Pair mates had similar chemical profiles in comparison with other breeding adults. Furthermore, we found evidence for sex differences and for changes across breeding stages. Notably, the preen oil of females was more diverse and more volatile than that of males, and the preen oil secreted by females during incubation was more volatile than that secreted during nestling rearing. However, we found no evidence for individual repeatability of chemical profiles across breeding stages in females. Our results point towards a function of preen oil in sexual signalling, although other functions should not be excluded. Our study is a first step towards understanding the role of odours in the social life of an important avian model species used in the study of mate choice and sexual selection.     

No evidence for pre-copulatory sexual selection on sperm length in a passerine bird

There is growing evidence that post-copulatory sexual selection, mediated by sperm competition, influences the evolution of sperm phenotypes. Evidence for pre-copulatory sexual selection effects on sperm traits, on the other hand, is rather scarce. A recent paper on the pied flycatcher, Ficedula hypoleuca, reported phenotypic associations between sperm length and two sexually selected male traits, i.e. plumage colour and arrival date, thus invoking pre-copulatory sexual selection for longer sperm. We were unable to replicate these associations with a larger data set from the same and two additional study populations; sperm length was not significantly related to either male plumage colour or arrival date. Furthermore, there was no significant difference in sperm length between populations despite marked differences in male plumage colour. We also found some evidence against the previously held assumption of longer sperm being qualitatively superior; longer sperm swam at the same speed as shorter sperm, but were less able to maintain speed over time. We argue that both empirical evidence and theoretical considerations suggest that the evolution of sperm morphology is not primarily associated with pre-copulatory sexual selection on male secondary sexual traits in this or other passerine bird species. The relatively large between-male variation in sperm length in this species is probably due to relaxed post-copulatory sexual selection.     

The feather mite (Astigmata) fauna of some passerine birds (Passeriformes) in the south of Western Siberia

Feather mites (Astigmata) are specialized parasites living on the plumage and skin of birds. The paper presents data on infestation of some passerines (Passeriformes) by feather mites in the south of Western Siberia (Omsk and Tyumen Provinces). We found 24 species of feather mites belonging to the families Analgidae, Dermoglyphidae, Pteronyssidae, Trouessartiidae, and Proctophyllodidae on 16 bird species. Among them, 19 species are common parasites of the passerine birds examined; five species were detected on atypical hosts. Ten mite species were recorded for the first time on the passerine species examined. Analysis of the distribution of abundant and common mite species on their hosts has demonstrated that the majority of the bird parasites possess a specific distribution pattern in the host plumage with preference for certain feather types. We have also obtained new data on host associations of several mite species.