Mycoplasmal Conjunctivitis Research Articles

Colder temperatures augment viability of an indirectly transmitted songbird pathogen on bird feeders

AbstractInanimate surfaces that are contaminated with infectious pathogens are common sources of spread for many communicable diseases. Understanding how ambient temperature alters the ability of pathogens to remain viable on these surfaces is critical for understanding how fomites can contribute to seasonal patterns of disease outbreaks. House finches (Haemorhous mexicanus) experience fall and winter outbreaks of mycoplasmal conjunctivitis, caused by the bacterial pathogen Mycoplasma gallisepticum (MG). Although bird feeder surfaces serve as an indirect route of MG transmission between sick and healthy individuals, the contributions of feeders to MG transmission in the wild will depend on how ambient temperature affects viability and pathogenicity of MG on feeder surfaces over time. Here, we used two experiments, with identical initial design, to assess such temperature effects. For both experiments, we pipetted equal amounts of MG onto replicate feeder ports held at night‐day temperatures representing summer (22–27°C) or winter (4–9°C). We allowed MG to incubate on feeders at either temperature and swabbed remaining inocula from surfaces at 0, 1, 2, 4, or 7 days post‐inoculation of the feeder, with each replicate feeder port only swabbed at a single time point. In the first study, we analyzed swabs using a culture‐based assay and found that MG incubated at colder versus warmer temperatures maintained higher viability on feeder surfaces over time. In the second study, we replicated the same experimental design but used MG swabs from feeder surfaces to inoculate wild‐caught, pathogen‐naïve birds and measured resulting disease severity and pathogen loads to determine pathogenicity. We found that MG remained pathogenic on feeder surfaces at cold ambient temperatures for up to one week, much longer than previously documented. Further, MG was significantly more pathogenic when incubated on feeders in colder versus warmer temperatures, with the strongest effects of temperature present after at least four days of incubation on feeder surfaces. Overall, cold ambient temperatures appear to alter the role of fomites in the MG transmission process, and temperature likely contributes to seasonal disease dynamics in this system and many others.

EFFECTS OF MYCOPLASMA GALLISEPTICUM INFECTION ON PREENING BEHAVIORS AND FEATHER QUALITY IN HOUSE FINCHES (HAEMORHOUS MEXICANUS).

Infections can have far-reaching sublethal effects on wildlife, including reduced maintenance of external structures. For many wildlife taxa, daily maintenance of external structures (termed preening in birds) is critical to fitness, but few studies have examined how infections alter such maintenance. Mycoplasma gallisepticum is a common pathogen in free-living House Finches (Haemorhous mexicanus), where it causes mycoplasmal conjunctivitis. Despite documented behavioral changes associated with M. gallisepticum infections in finches, no studies have examined how preening behavior may change with infection and how potential differences in preening may affect feather quality. To test this, we experimentally inoculated captive House Finches with M. gallisepticum or a control treatment, and we collected behavioral and feather quality data to detect potential changes in feather maintenance due to infection. We found that finches infected with M. gallisepticum preened significantly less often, and within the infected treatment, birds with the highest conjunctivitis severity preened the least often. However, there was no difference in the quality scores for secondary flight feathers collected from control versus infected birds. We also assayed feather water retention and found that the degree of water retention correlated with our feather quality scores, such that feathers with poor scores retained more water. However, as with quality scores, feather water retention did not differ with infection; this may be due to the controlled environment that the birds experienced while in captivity. Our data suggest that, in addition to sickness behaviors previously observed in finches, M. gallisepticum infection decreases other behaviors critical to survival, such as preening. While the consequences of reduced preening on feather maintenance were not apparent in captive conditions, further work is needed to determine whether House Finches in the wild that are infected with M. gallisepticum experience a fitness cost, such as increases in ectoparasite loads, due to this reduced feather maintenance.

Protection Generated by Prior Exposure to Pathogens Depends on both Priming and Challenge Dose.

Free-living hosts encounter pathogens at a wide range of frequencies and concentrations, including low doses that are largely aclinical, creating a varied landscape of exposure history and reinfection likelihood. While several studies show that higher priming doses result in stronger immunological protection against reinfection, it remains unknown how the reinfection challenge dose and priming dose interact to determine the likelihood and severity of reinfection. We manipulated both priming and challenge doses of Mycoplasma gallisepticum, which causes mycoplasmal conjunctivitis, in captive house finches (Haemorhous mexicanus), to assess reinfection probability and severity. We found a significant interaction between priming and challenge doses on reinfection probability, with the likelihood of reinfection by a high but not a low challenge dose decreasing exponentially at higher priming doses. While this interaction was likely driven by lower average infection probabilities for low-dose versus high-dose challenges, even the highest priming dose provided only negligible protection against reinfection from low-dose challenges. Similarly, pathogen loads during reinfection were significantly reduced with increasing priming doses only for birds reinfected at high but not low doses. We hypothesize that these interactions arise to some degree from fundamental differences in host immune responses across doses, with single low doses only weakly triggering host immune responses. Importantly, our results also demonstrate that reinfections can occur from a variety of exposure doses and across diverse degrees of standing immunity in this system. Overall, our study highlights the importance of considering both initial and subsequent exposure doses where repeated exposure to a pathogen is common in nature.

Disease tolerance alters host competence in a wild songbird.

Individuals can express a range of disease phenotypes during infection, with important implications for epidemics. Tolerance, in particular, is a host response that minimizes the per-pathogen fitness costs of infection. Because tolerant hosts show milder clinical signs and higher survival, despite similar pathogen burdens, their potential for prolonged pathogen shedding may facilitate the spread of pathogens. To test this, we simulated outbreaks of mycoplasmal conjunctivitis in house finches, asking how the speed of transmission varied with tissue-specific and behavioural components of tolerance, milder conjunctivitis and anorexia for a given pathogen load, respectively. Because tissue-specific tolerance hinders pathogen deposition onto bird feeders, important transmission hubs, we predicted it would slow transmission. Because behavioural tolerance should increase interactions with bird feeders, we predicted it would speed transmission. Our findings supported these predictions, suggesting that variation in tolerance could help identify individuals most likely to transmit pathogens.

Body condition and poxvirus infection predict circulating glucose levels in a colorful songbird that inhabits urban and rural environments.

There is widespread contemporary interest in causes and consequences of blood glucose status in humans (e.g., links to diabetes and cardiovascular disease), but we know comparatively less about what underlies variation in glucose levels of wild animals. Several environmental factors, including diet, disease status, and habitat quality, may regulate glucose circulation, and we are in need of work that assesses many organismal traits simultaneously to understand the plasticity and predictability of glucose levels in ecological and evolutionary contexts. Here, we measured circulating glucose levels in a species of passerine bird (the house finch, Haemorhous mexicanus) that has served as a valuable model for research on sexual selection, disease, and urban behavioral ecology, as these animals display sexually dichromatic ornamental coloration, harbor many infectious diseases (e.g., poxvirus, coccidiosis, mycoplasmal conjunctivitis), and reside in both natural habitats and cities. We tested the effects of sex, habitat type, body condition, coccidiosis and poxvirus infections, and expression of carotenoid plumage coloration on blood glucose concentrations and found that the body condition and poxvirus infection significantly predicted circulating glucose levels. Specifically, birds with higher blood glucose levels had higher body condition scores and were infected with poxvirus. This result is consistent with biomedical, domesticated-animal, and wildlife-rehabilitation findings, and the premise that glucose elevation is a physiological response to or indicator of infection and relative body weight. The fact that we failed to find links between glucose and our other measurements suggests that blood glucose levels can reveal some but not all aspects of organismal or environmental quality.

Characterization of unilateral conjunctival inoculation with Mycoplasma gallisepticum in house finches

ABSTRACTHouse finches in much of the continental United States experience annual epidemics of mycoplasmal conjunctivitis, caused by the bacterial pathogen Mycoplasma gallisepticum (MG). Although evidence suggests that natural infections typically begin unilaterally, experimental inoculations of songbirds with MG to date have all been administered bilaterally. Furthermore, studies of free-living finches find more severe clinical signs of mycoplasmal conjunctivitis in left versus right eyes, but the mechanisms underlying this side bias remain unknown. Here, we characterized unilateral inoculation of house finches with MG, and tested whether differential susceptibility of left versus right conjunctiva explains the side bias in disease severity of free-living finches. We directly inoculated house finches in either the left or right conjunctiva and characterized resulting disease severity and pathogen load throughout the course of infection. As expected, unilateral inoculation resulted in significantly more severe conjunctivitis, as well as higher conjunctival bacterial loads, on whichever side (left or right) birds were directly inoculated. However, in 55% of cases, unilateral inoculations resulted in bilateral disease, and in 85% cases there was evidence of bilateral infection. The overall severity of disease did not differ for birds inoculated in the left versus right conjunctiva, suggesting that physiological differences between the conjunctivae cannot explain the side bias in disease severity of free-living birds. Instead, laterality in exposure, perhaps due to feeding handedness, likely explains the detected field patterns.RESEARCH HIGHLIGHTSHouse finches show more severe disease in the directly inoculated conjunctiva.Unilateral inoculations lead to high rates of bilateral infection and disease.Overall disease severity does not differ for the left- or right-inoculated conjunctiva.Laterality in exposure likely explains the left-side bias in natural infections.

Differing House Finch Cytokine Expression Responses to Original and Evolved Isolates of Mycoplasma gallisepticum.

The recent emergence of the poultry bacterial pathogen Mycoplasma gallisepticum (MG) in free-living house finches (Haemorhous mexicanus), which causes mycoplasmal conjunctivitis in this passerine bird species, resulted in a rapid coevolutionary arms-race between MG and its novel avian host. Despite extensive research on the ecological and evolutionary dynamics of this host–pathogen system over the past two decades, the immunological responses of house finches to MG infection remain poorly understood. We developed seven new probe-based one-step quantitative reverse transcription polymerase chain reaction assays to investigate mRNA expression of house finch cytokine genes (IL1B, IL6, IL10, IL18, TGFB2, TNFSF15, and CXCLi2, syn. IL8L). These assays were then used to describe cytokine transcription profiles in a panel of 15 house finch tissues collected at three distinct time points during MG infection. Based on initial screening that indicated strong pro-inflammatory cytokine expression during MG infection at the periorbital sites in particular, we selected two key house finch tissues for further characterization: the nictitating membrane, i.e., the internal eyelid in direct contact with MG, and the Harderian gland, the secondary lymphoid tissue responsible for regulation of periorbital immunity. We characterized cytokine responses in these two tissues for 60 house finches experimentally inoculated either with media alone (sham) or one of two MG isolates: the earliest known pathogen isolate from house finches (VA1994) or an evolutionarily more derived isolate collected in 2006 (NC2006), which is known to be more virulent. We show that the more derived and virulent isolate NC2006, relative to VA1994, triggers stronger local inflammatory cytokine signaling, with peak cytokine expression generally occurring 3–6 days following MG inoculation. We also found that the extent of pro-inflammatory interleukin 1 beta signaling was correlated with conjunctival MG loads and the extent of clinical signs of conjunctivitis, the main pathological effect of MG in house finches. These results suggest that the pathogenicity caused by MG infection in house finches is largely mediated by host pro-inflammatory immune responses, with important implications for the dynamics of host–pathogen coevolution.

Eye of the Finch: characterization of the ocular microbiome of house finches in relation to mycoplasmal conjunctivitis.

Vertebrate ocular microbiomes are poorly characterized and virtually unexplored in wildlife species. Pathogen defense is considered a key function of microbiomes, but determining microbiome stability during disease is critical for understanding the role of resident microbial communities in infectious disease dynamics. Here, we characterize the ocular bacterial microbiome of house finches (Haemorhous mexicanus), prior to and during experimental infection with an inflammatory ocular disease, Mycoplasmal conjunctivitis, caused by Mycoplasma gallisepticum. In ocular tissues of healthy house finches, we identified 526 total bacterial operational taxonomic units (OTUs, 97% similarity), primarily from Firmicutes (92.6%) and Proteobacteria (6.9%), via 16S rRNA gene amplicon sequencing. Resident ocular communities of healthy female finches were characterized by greater evenness and phylogenetic diversity compared to healthy male finches. Regardless of sex, ocular microbiome community structure significantly shifted 11 days after experimental inoculation with M. gallisepticum. A suite of OTUs, including taxa from the genera Methylobacterium, Acinetobacter and Mycoplasma, appear to drive these changes, indicating that the whole finch ocular microbiome responds to infection. Further study is needed to quantify changes in absolute abundance of resident taxa and to elucidate potential functional roles of the resident ocular microbiome in mediating individual responses to this common songbird bacterial pathogen.

Direct and indirect effects of anthropogenic bird food on population dynamics of a songbird

Anthropogenic bird foods are frequently credited with affecting avian population dynamics, but few studies have tested this assertion over broad spatial scales. Human-derived foods could directly impact population sizes or indirectly affect them by mediating the influence of another factor, such as disease. In 1994, a novel disease outbreak (mycoplasmal conjunctivitis) substantially reduced populations of the house finch (Haemorhous mexicanus) in the eastern United States, creating an opportunity to test whether bird feeding indirectly exacerbated or ameliorated the impacts of the disease. We assessed the effects of bird food availability on house finch populations using data from the National Survey on Fishing, Hunting, and Wildlife-associated Recreation and the Christmas Bird Count. House finch densities were positively related to the density of people providing food for birds prior to the spread of mycoplasmal conjunctivitis, suggesting that the availability of bird seed can limit the size of finch populations. Following the disease epidemic, house finch declines were greatest where the density of people feeding birds also fell dramatically. This pattern suggests that bird food could have a positive indirect effect on disease-related mortality. Our findings suggest that the collective actions of individual people have the potential to influence resource availability and population dynamics of wildlife in human-modified landscapes.

Do infections lead to higher feather mite loads in birds? A test with mycoplasmal conjunctivitis in House Finches (Haemorhous mexicanus)

Abstract. Current evidence suggests that the health effect of avian feather mites is minimal. However, feather mites can still proliferate without effective preening, such as might occur during sickness. House Finches (Haemorhous mexicanus) are prone to infection by Mycoplasma gallisepticum, symptoms of which include conjunctivitis. Impaired vision and lethargy associated with the disease may limit preening ability. We examined trapping data from a 4-year study of Mycoplasma infection dynamics in House Finches in Atlanta, Georgia, to determine whether birds with conjunctivitis had higher feather mite loads. Abundance of feather mites (Proctophyllodes spp.) and conjunctivitis severity were visually scored on >800 House Finches of known age and sex. Feather mite abundance showed a distinct seasonal pattern: mite loads increased in July and remained high through January. Limiting the analyses to these months, we found that average mite scores were higher in birds with (n = 94) than in those without (n = 275)...

Ketocarotenoid circulation, but not retinal carotenoid accumulation, is linked to eye disease status in a wild songbird

Pathogenic or parasitic infections pose numerous physiological challenges to organisms. Carotenoid pigments have often been used as biomarkers of disease state and impact because they integrate multiple aspects of an individual’s condition and nutritional and health state. Some diseases are known to influence carotenoid uptake from food (e.g. coccidiosis) and carotenoid use (e.g. as antioxidants/immunostimulants in the body, or for sexually attractive coloration), but there is relatively little information in animals about how different types of carotenoids from different tissue sources may be affected by disease. Here we tracked carotenoid accumulation in two body pools (retina and plasma) as a function of disease state in free-ranging house finches (Haemorhous mexicanus). House finches in eastern North America can contract mycoplasmal conjunctivitis (Mycoplasma gallisepticum, or MG), which can progress from eye swelling to eye closure and death. Previous work showed that systemic immune challenges in house finches lower carotenoid levels in retina, where they act as photoprotectors and visual filters. We assessed carotenoid levels during the molt period, a time of year when finches uniquely metabolize ketocarotenoids (e.g. 3-hydroxy-echinenone) for acquisition of sexually selected red plumage coloration, and found that males infected with MG circulated significantly lower levels of 3-hydroxy-echinenone, but no other plasma carotenoid types, than birds exhibiting no MG symptoms. This result uncovers a key biochemical mechanism for the documented detrimental effect of MG on plumage redness in H. mexicanus. In contrast, we failed to find a relationship between MG infection status and retinal carotenoid concentrations. Thus, we reveal differential effects of an infectious eye disease on carotenoid types and tissue pools in a wild songbird. At least compared to retinal sources (which appear somewhat more temporally stable than other body carotenoid pools, even to diseases of the eye evidently), our results point to either a high physiological cost of ketocarotenoid synthesis (as is argued in models of sexually selected carotenoid coloration) or high benefit of using this ketocarotenoid to combat infection.

CAN AMERICAN GOLDFINCHES FUNCTION AS RESERVOIRS FOR MYCOPLASMA GALLISEPTICUM?

We performed experiments to test if American Goldfinches (Spinus tristis) could be a competent reservoir for Mycoplasma gallisepticum and play a role in the epidemic spread of mycoplasmal conjunctivitis among House Finches (Carpodacus mexicanus) in North America. We infected one of two individuals housed together in a cage and determined if transmission occurred to the second bird. Probability of transmission between an American Goldfinch and a House Finch (in either direction) was similar to that between two House Finches. In a second experiment small groups of birds (6-8) were housed in large aviaries. Two source birds were inoculated with M. gallisepticum, and transmission to the naive birds in the aviary was recorded. Transmission occurred among House Finches, among American Goldfinches, and from House Finches to American Goldfinches. Transmission was more likely between House Finches than among American Goldfinches, and between House Finches and American Goldfinches. We conclude that American Goldfinches are a competent reservoir for Mycoplasma gallisepticum and could have played a role in the spread of the epidemic as they are more migratory than House Finches.

Understanding the origin of seasonal epidemics of mycoplasmal conjunctivitis

1. Many host-pathogen systems show regular seasonal oscillations. 2. Seasonal variation in mycoplasmal conjunctivitis prevalence in house finches is an example of such oscillations. 3. An annual pulse of Mycoplasma gallisepticum-naïve juveniles increasing the number of susceptibles, seasonal changes in flocking behaviour increasing transmission rate and a gradual loss of resistance to reinfection with time are sufficient to model the observed seasonal variation in disease prevalence. Nevertheless, experiments are needed to test the underlying mechanisms. 4. We carried out an 18-month experiment with small groups of birds in large aviaries to test two hypotheses. 5. To test the first hypothesis that an influx of naïve juveniles in a group of recovered adults is sufficient to cause an outbreak, we added eight juveniles to a group of 11 adults that had recovered from an earlier infection. In all, three replicates juveniles became infected, but only after some of the adults relapsed. 6. To test the second hypothesis that reintroduction of M. gallisepticum into a multiage group of previously exposed but fully recovered house finches causes a new outbreak, we inoculated two birds in each group in March of the 2nd year. Contrary to what happens in the wild at that time disease prevalence increased rapidly after reintroduction of M. gallisepticum. 7. We conclude that asymptomatic, recovered adults can initiate an epidemic and transmit M. gallisepticum to naïve house finches and that the reintroduction of M. gallisepticum is sufficient to cause a new outbreak, even at a time of the year when mycoplasmal conjunctivitis is low in free-living birds. Date, as such, seems to be less important to explain seasonal variation in conjunctivitis than the presence of naïve juveniles or the introduction on M. gallisepticum. 8. Seasonality in outbreaks is most likely tightly linked to seasonal variation in bird movements and behaviour.

Contrasting epidemic histories reveal pathogen-mediated balancing selection on class II MHC diversity in a wild songbird.

The extent to which pathogens maintain the extraordinary polymorphism at vertebrate Major Histocompatibility Complex (MHC) genes via balancing selection has intrigued evolutionary biologists for over half a century, but direct tests remain challenging. Here we examine whether a well-characterized epidemic of Mycoplasmal conjunctivitis resulted in balancing selection on class II MHC in a wild songbird host, the house finch (Carpodacus mexicanus). First, we confirmed the potential for pathogen-mediated balancing selection by experimentally demonstrating that house finches with intermediate to high multi-locus MHC diversity are more resistant to challenge with Mycoplasma gallisepticum. Second, we documented sequence and diversity-based signatures of pathogen-mediated balancing selection at class II MHC in exposed host populations that were absent in unexposed, control populations across an equivalent time period. Multi-locus MHC diversity significantly increased in exposed host populations following the epidemic despite initial compromised diversity levels from a recent introduction bottleneck in the exposed host range. We did not observe equivalent changes in allelic diversity or heterozygosity across eight neutral microsatellite loci, suggesting that the observations reflect selection rather than neutral demographic processes. Our results indicate that a virulent pathogen can exert sufficient balancing selection on class II MHC to rescue compromised levels of genetic variation for host resistance in a recently bottlenecked population. These results provide evidence for Haldane's long-standing hypothesis that pathogens directly contribute to the maintenance of the tremendous levels of genetic variation detected in natural populations of vertebrates.

Mycoplasmal Conjunctivitis in House Finches (Carpodacus Mexicanus) is More Severe in Left Eyes than Right

One of the most well-studied avian diseases is the annual outbreak of Mycoplasma gallisepticum (MG) infections in house finches (Carpodacus mexicanus) in North America. This is a bacterial disease that causes conjunctivitis in one or both eyes of the host. While studying this disease in a New York finch population, researchers observed that there was a tendency for the conjunctivitis to be more prominent in the left eye of infected birds, although the small sample size of that study made it difficult to draw conclusions regarding this unusual observation. Here, this idea is tested further using a larger data set from a 4-year trapping study of house finches in Atlanta, Georgia, USA, a location with a high prevalence of MG infections. The severity of conjunctivitis in each eye of infected birds was scored on a 0–3 scale, and these data were statistically examined to identify possible side-biases in severity. Out of 254 house finches with conjunctivitis, the eye scores of all left eyes were significantly higher than right eye scores. There was no evidence for differential effects of conjunctivitis in left-bias or right-biased infections, and the left-biased pattern was similar in both sexes and in adult and young birds. These results confirm the anecdotal observation from the New York population and suggest that this is a universal phenomenon in the house finch–MG system. The significance of the finding is unknown, although the possibility exists that house finches display a degree of ‘handedness’ that causes their left sides to be exposed more frequently to potential fomites (i.e. bird feeders).

Common garden experiment reveals pathogen isolate but no host genetic diversity effect on the dynamics of an emerging wildlife disease

Host genetic diversity can mediate pathogen resistance within and among populations. Here we test whether the lower prevalence of Mycoplasmal conjunctivitis in native North American house finch populations results from greater resistance to the causative agent, Mycoplasma gallisepticum (MG), than introduced, recently-bottlenecked populations that lack genetic diversity. In a common garden experiment, we challenged wild-caught western (native) and eastern (introduced) North American finches with a representative eastern or western MG isolate. Although introduced finches in our study had lower neutral genetic diversity than native finches, we found no support for a population-level genetic diversity effect on host resistance. Instead we detected strong support for isolate differences: the MG isolate circulating in western house finch populations produced lower virulence, but higher pathogen loads, in both native and introduced hosts. Our results indicate that contemporary differences in host genetic diversity likely do not explain the lower conjunctivitis prevalence in native house finches, but isolate-level differences in virulence may play an important role.

The Potential Impact of Disease on the Migratory Structure of a Partially Migratory Passerine Population

Since its introduction into eastern North America in the 1940s, the eastern population of house finches (Carpodacus mexicanus) has become partially migratory, unlike its nonmigratory source population in southern California (Able and Belthoff in Proc. R. Soc. Lond. 265 (1410), 2063-2071, 1998; Belthoff and Gauthreaux in Condor 93, 374-382, 1991). The infectious disease mycoplasmal conjunctivitis (pathogen Mycoplasma gallisepticum or "MG"), which has been monitored in the house finch population since its appearance around 1993 (Dhondt et al. in J. Wild. Dis. 34 (2), 265-280, 1998), may induce higher mortality rates among populations in more northerly latitudes relative to more southerly populations. Here, we investigate the potential impact of this differential disease mortality on the migratory structure of the eastern house finch population using an epidemic modeling approach. Analytical and computational results suggest the ongoing MG epidemic in the eastern house finch could lead to increases in the percentage of and the total number of migrating individuals in a population despite overall population declines, assuming relatively high winter mortality rates in the north eastern part of their range. These results also suggest that empirical evidence of such a change in migratory structure would be most noticeable in northerly inland populations that showed significant declines following the initial outbreak of MG in the east.

Factors Influencing Fidelity Of House Finches To A Feeding Station

House Finches (Carpodacus mexicanus) in North America are a commonly-studied species, but basic aspects of their life history remain poorly understood. I banded and observed marked House Finches at a backyard feeding site in a suburban neighborhood in Atlanta, Georgia from August 2002 through July 2004 to address how age, gender, mycoplasmal conjunctivitis, and time of year affected fidelity of individual House Finches to this site. Of 386 House Finches banded, I recaptured 77 and recorded 1,210 reobservations. More than half (55%) of all birds banded were not seen again and, of those that were, almost half (44%) were seen for less than 2 months. A House Finch's age, gender, and month of capture significantly affected how many times it was subsequently encountered (recaptured or reobserved), but not the duration of time it spent at the site of banding. Young birds (HYs) were encountered more often than adults (AHYs), and females more than males. Young birds with mycoplasmal conjunctivitis were encountered less often than those without, but this was not true for adults. These data indicate high site fidelity of adults during the breeding season and low site fidelity of juveniles early in the summer that becomes higher in late summer. Most birds captured in fall were encountered for up to 3 months. These results are discussed in relation to previous studies and their implications for transmission of Mycoplasma gallisepticum among House Finches.

Experimental evidence for transmission of Mycoplasma gallisepticum in house finches by fomites

Ever since Mycoplasma gallisepticum emerged among house finches in North America, it has been suggested that bird aggregations at feeders are an important cause of the epidemic of mycoplasmal conjunctivitis because diseased birds could deposit droplets of pathogen onto the feeders and thereby promote indirect transmission by fomites. In this paper we bring the first experimental evidence that such transmission (bird-to-feeder-to-bird) does actually take place. House finches infected via this route, however, developed only mild disease and recovered much more rapidly than birds infected from the same source birds but directly into the conjunctiva. While it is certainly probable that house finch aggregations at artificial feeders enhance pathogen transmission, to some degree transmission of M. gallisepticum by fomites may serve to immunize birds against developing more severe infections. Some such birds develop M. gallisepticum antibodies, providing indication of an immune response, although no direct evidence of protection.

CONTRASTING NATURAL EXPERIMENTS CONFIRM COMPETITION BETWEEN HOUSE FINCHES AND HOUSE SPARROWS

After House Finches were introduced from the western to the eastern United States and rapidly increased in numbers, House Sparrows declined, leading to suggestions that the decline was caused by interspecific competition. However, other potential causes were not excluded. The rapid decline in House Finches following the emergence of a new disease (mycoplasmal conjunctivitis) caused by a novel strain of Mycoplasma gallisepticum (MG) in 1994 has provided a natural experiment and an opportunity to revisit the hypothesis that interspecific competition from House Finches drives population changes in House Sparrows. If true, the recent decline in House Finches should lead to an increase in House Sparrows. In this paper we test the hypothesis that House Sparrow and House Finch numbers in the northeastern United States vary inversely by examining data from three independent volunteer programs that monitor bird species' abundance and distribution (Christmas Bird Count, Project FeederWatch, and Breeding Bird Survey). In the first analysis we found that House Sparrow and House Finch numbers varied inversely during a time interval when House Finches were increasing and a time interval when House Finches were decreasing. In the second analysis, we found that the rates of geometric change in House Sparrow abundance (ln[HOSP(t+1)/HOSP(t)]) were negatively correlated with initial House Finch (HOFI(t)) and sparrow (HOSP(t)) abundances at individual sites, irrespective of the time period. Given that finch range expansion and subsequent declines in abundance are the result of two very different phenomena, it would be very unlikely for apparent competition or spurious correlations to cause the observed concomitant changes in House Sparrow abundance. We conclude that interspecific competition exists between these two species.