Parasites favour intermediate nestling mass and brood size in cliff swallows.

A challenge of life-history theory is to explain why animal body size does not continue to increase, given various advantages of larger size. In birds, body size of nestlings and the number of nestlings produced (brood size) have occasionally been shown to be constrained by higher predation on larger nestlings and those from larger broods. Parasites also are known to have strong effects on life-history traits in birds, but whether parasitism can be a driver for stabilizing selection on nestling body size or brood size is unknown. We studied patterns of first-year survival in cliff swallows (Petrochelidon pyrrhonota) in western Nebraska in relation to brood size and nestling body mass in nests under natural conditions and in those in which hematophagous ectoparasites had been removed by fumigation. Birds from parasitized nests showed highest first-year survival at the most common, intermediate brood-size and nestling-mass categories, but cliff swallows from nonparasitized nests had highest survival at the heaviest nestling masses and no relationship with brood size. A survival analysis suggested stabilizing selection on brood size and nestling mass in the presence (but not in the absence) of parasites. Parasites apparently favour intermediate offspring size and number in cliff swallows and produce the observed distributions of these traits, although the mechanisms are unclear. Our results emphasize the importance of parasites in life-history evolution.

Environmental determinants of haemosporidian parasite prevalence in a declining population of Tree swallows.

The prevalence of vector-borne parasites such as haemosporidian species is influenced by several environmental factors. While the negative effects of parasitism on hosts are well documented, these can also be amplified by interactions with environmental stressors, many of which are anthropogenic. Yet, we know little about the possible effects of anthropogenic perturbations on parasite prevalence. The goals of this study were to assess the prevalence and environmental determinants of haemosporidian parasites in a declining population of Tree swallows (Tachycineta bicolor) living in an agricultural landscape in southern Québec, Canada. Overall, a low prevalence and a moderate lineage diversity were identified in both adults and nestlings, confirming that transmission can occur during the breeding period. Anthropic areas, extensive cultures (hayfields and pastures) and forest cover within 500 km of nest boxes, as well as daily temperature fluctuations, were all related to infection by haemosporidian parasites. These findings suggest that anthropogenic alterations of landscape composition can modulate the prevalence of haemosporidian parasites in Tree swallows. Our results represent a baseline for future comparative studies assessing haemosporidian parasite prevalence in human-modified landscapes.

Hematophagous Ectoparasites of Cliff Swallows Invade a Hospital and Feed on Humans.

We describe a hospital infestation by 2 hematophagous ectoparasites of cliff swallows that nested in the window eaves. Breaks in window seals allowed entry of swallow ticks and swallow bugs. These pests emerged in large numbers in patient rooms, hallways, and stairwells; 17% of the ticks fed on humans.

Transcontinental migratory connectivity predicts parasite prevalence in breeding populations of the European barn swallow.

Parasites exert a major impact on the eco-evolutionary dynamics of their hosts and the associated biotic environment. Migration constitutes an effective means for long-distance invasions of vector-borne parasites and promotes their rapid spread. Yet, ecological and spatial information on population-specific host-parasite connectivity is essentially lacking. Here, we address this question in a system consisting of a transcontinental migrant species, the European barn swallow (Hirundo rustica) which serves as a vector for avian endoparasites in the genera Plasmodium, Haemoproteus and Leucocytozoon. Using feather stable isotope ratios as geographically informative markers, we first assessed migratory connectivity in the host: Northern European breeding populations predominantly overwintered in dry, savannah-like habitats in Southern Africa, whereas Southern European populations were associated with wetland habitats in Western Central Africa. Wintering areas of swallows breeding in Central Europe indicated a migratory divide with both migratory programmes occurring within the same breeding population. Subsequent genetic screens of parasites in the breeding populations revealed a link between the host's migratory programme and its parasitic repertoire: controlling for effects of local breeding location, prevalence of Africa-transmitted Plasmodium lineages was significantly higher in individuals overwintering in the moist habitats of Western Central Africa, even among sympatrically breeding individuals with different overwintering locations. For the rarer Haemoproteus parasites, prevalence was best explained by breeding location alone, whereas no clear pattern emerged for the least abundant parasite Leucocytozoon. These results have implications for our understanding of spatio-temporal host-parasite dynamics in migratory species and the spread of avian borne diseases.

Dispersing hemipteran vectors have reduced arbovirus prevalence.

A challenge in managing vector-borne zoonotic diseases in human and wildlife populations is predicting where epidemics or epizootics are likely to occur, and this requires knowing in part the likelihood of infected insect vectors dispersing pathogens from existing infection foci to novel areas. We measured prevalence of an arbovirus, Buggy Creek virus, in dispersing and resident individuals of its exclusive vector, the ectoparasitic swallow bug (Oeciacus vicarius), that occupies cliff swallow (Petrochelidon pyrrhonota) colonies in western Nebraska. Bugs colonizing new colony sites and immigrating into established colonies by clinging to the swallows' legs and feet had significantly lower virus prevalence than bugs in established colonies and those that were clustering in established colonies before dispersing. The reduced likelihood of infected bugs dispersing to new colony sites indicates that even heavily infected sites may not always export virus to nearby foci at a high rate. Infected arthropods should not be assumed to exhibit the same dispersal or movement behaviour as uninfected individuals, and these differences in dispersal should perhaps be considered in the epidemiology of vector-borne pathogens such as arboviruses.

Elevated Temperature Reduces Overwintering Survival of an Avian Ectoparasite, the Swallow Bug (Hemiptera: Cimicidae: Cimex vicarius).

The survival of insects that are dormant in winter may either increase or decrease as a consequence of elevated winter temperatures under climate change. Warming can be deleterious when metabolism of the overwintering life stages increases to the point that energy reserves are exhausted before postoverwintering reemergence. We examined experimentally how overwintering survival of swallow bugs (Hemiptera: Cimicidae: Cimex vicarius Horvath), an ectoparasite primarily of cliff swallows (Passeriformes: Hirundinidae: Petrochelidon pyrrhonota Vieillot), was affected by a 3°C rise in mean daily temperature for populations in Oklahoma, Nebraska, and North Dakota. Adult and nymphal swallow bugs exposed to elevated temperature had an average reduction of approximately 31% in overwintering survival (from July/August to April/May), relative to controls exposed to current region-specific ambient-like conditions. Adult males in both groups survived less well in Nebraska and North Dakota than adult males in Oklahoma, but there was no consistent latitudinal effect of the elevated heat treatment. Our results indicate that projected increases in mean temperature in the Great Plains by 2050 could result in fewer swallow bugs surviving the winter and thus a reduced population size upon the arrival of their primary host in the spring, potentially affecting cliff swallow reproductive success, site use, and breeding phenology. Global climate change may alter the dynamics of host-parasite systems by reducing overall parasite abundance.

Change in beak overhangs of cliff swallows over 40 years: Partly a response to parasites?

Some birds exhibit a maxillary overhang, in which the tip of the upper beak projects beyond the lower mandible and may curve downward. The overhang is thought to help control ectoparasites on the feathers. Little is known about the extent to which the maxillary overhang varies spatially or temporally within populations of the same species. The colonial cliff swallow (Petrochelidon pyrrhonota) has relatively recently shifted to almost exclusive use of artificial structures such as bridges and highway culverts for nesting and consequently has been exposed to higher levels of parasitism than on its ancestral cliff nesting sites. We examined whether increased ectoparasitism may have favored recent changes in the extent of the maxillary overhang. Using a specimen collection of cliff swallows from western Nebraska, USA, spanning 40 years and field data on live birds, we found that the extent of the maxillary overhang increased across years in a nonlinear way, peaking in the late 2000's, and varied inversely with cliff swallow colony size for unknown reasons. The number of fleas on nestling cliff swallows declined in general over this period. Those birds with perceptible overhangs had fewer swallow bugs on the outside of their nest, but they did not have higher nesting success than birds with no overhangs. The intraspecific variation in the maxillary overhang in cliff swallows was partly consistent with it having a functional role in combatting ectoparasites. The temporal increase in the extent of the overhang may be a response by cliff swallows to their relatively recent increased exposure to parasitism. Our results demonstrate that this avian morphological trait can change rapidly over time.

An enzootic vector-borne virus is amplified at epizootic levels by an invasive avian host.

Determining the effect of an invasive species on enzootic pathogen dynamics is critical for understanding both human epidemics and wildlife epizootics. Theoretical models suggest that when a naive species enters an established host-parasite system, the new host may either reduce ('dilute') or increase ('spillback') pathogen transmission to native hosts. There are few empirical data to evaluate these possibilities, especially for animal pathogens. Buggy Creek virus (BCRV) is an arthropod-borne alphavirus that is enzootically transmitted by the swallow bug (Oeciacus vicarius) to colonially nesting cliff swallows (Petrochelidon pyrrhonota). In western Nebraska, introduced house sparrows (Passer domesticus) invaded cliff swallow colonies approximately 40 years ago and were exposed to BCRV. We evaluated how the addition of house sparrows to this host-parasite system affected the prevalence and amplification of a bird-associated BCRV lineage. The infection prevalence in house sparrows was eight times that of cliff swallows. Nestling house sparrows in mixed-species colonies were significantly less likely to be infected than sparrows in single-species colonies. Infected house sparrows circulated BCRV at higher viraemia titres than cliff swallows. BCRV detected in bug vectors at a site was positively associated with virus prevalence in house sparrows but not with virus prevalence in cliff swallows. The addition of a highly susceptible invasive host species has led to perennial BCRV epizootics at cliff swallow colony sites. The native cliff swallow host confers a dilution advantage to invasive sparrow hosts in mixed colonies, while at the same sites house sparrows may increase the likelihood that swallows become infected.

Collyriclosis in Central European hirundines.

Cutaneous monostome trematode Collyriclum faba (Bremser in Schmalz 1831) is a digenetic flatworm with unknown life cycle. Here, we provide the first compelling evidence that despite low prevalence of the parasite, European hirundines are parasitized by this species. First host record for sand martin (Riparia riparia) and first European host record for barn swallow (Hirundo rustica) is provided. The birds were captured and checked in ten European and Middle Eastern countries, stretching from Ireland to Bahrain, but only samples from Central Europe (Czech Republic, Hungary and Poland) were positive for C. faba. In total, 164,582 sand martins and 100,443 barn swallows were examined, and seven and two birds had cutaneous C. faba cysts. Even though over 40% of the birds captured were juveniles, all but one infected individuals were adults, equally both males and females. The prevalence of the parasite on Central European hirundines were calculated as one in 20,641 for sand martins and one in 4,484 for barn swallows. All the infected birds were captured in close vicinity of water bodies. All the cysts were found close to the vent or on the legs. No adverse effects on its bird hosts were observed.

Molecular and MALDI-TOF MS identification of swallow bugs Cimex hirundinis (Heteroptera: Cimicidae) and endosymbionts in France.

BACKGROUND: The Cimicidae are obligatory blood-feeding ectoparasites of medical and veterinary importance. We aim in the current study to assess the ability of MALDI-TOF MS to identify Cimex hirundinis swallow bugs collected in house martin nests. METHODS: Swallow bugs were picked out from abandoned nests of house martin swallows and identified morphologically to the species level. The bugs were randomly selected, dissected and then subjected to MALDI-TOF MS and molecular analyses. RESULTS: A total of 65 adults and 50 nymphs were used in the attempt to determine whether this tool could identify the bug species and discriminate their developmental stages. Five adults and four nymphs of C. hirundinis specimens were molecularly identified to update our MS homemade arthropod database. BLAST analysis of COI gene sequences from these C. hirundinis revealed 98.66-99.12% identity with the corresponding sequences of C. hirundinis of the GenBank. The blind test against the database supplemented with MS reference spectra showed 100% (57/57) C. hirundinis adults and 100% (46/46) C. hirundinis nymphs were reliably identified and in agreement with morphological identification with logarithmic score values between 1.922 and 2.665. Ninety-nine percent of C. hirundinis specimens tested were positive for Wolbachia spp. The sequencing results revealed that they were identical to Wolbachia massiliensis, belonging to the new T-supergroup strain and previously isolated from C. hemipterus. CONCLUSIONS: We report for the first time to our knowledge a case of human infestation by swallow bugs (C. hirundinis) in France. We also show the usefulness of MALDI-TOF MS in the rapid identification of C. hirundinis specimens and nymphs with minimal sample requirements. We phylogenetically characterized the novel Wolbachia strain (W. massiliensis) infecting C. hirundinis and compared it to other recognized Wolbachia clades.

DIPLOTRIAENA OBTUSA (NEMATODA: DIPLOTRIAENIDAE) FROM BARN SWALLOWS (HIRUNDO RUSTICA) AND CLIFF SWALLOWS (PETROCHELIDON PYRRHONOTA) COLLECTED DURING MORTALITY EVENTS IN THE UPPER MIDWEST, USA.

Several mortality events involving barn swallows (Hirundo rustica) and cliff swallows (Petrochelidon pyrrhonota) were reported in the Upper Midwestern states in 2017 and 2018. Barn swallow mortality followed unseasonal cold snaps, with the primary cause of death being emaciation with concurrent air sac nematodiasis. Lesions in cliff swallows were consistent with blunt force trauma from suspected car impacts. Examination of air sac nematodes from both bird species revealed morphological characters consistent with Diplotriaena obtusa. Sequence analysis of the partial 18S rRNA gene indicated the samples clustered with other species in the genus Diplotriaena. These nematodes provide a link between morphological specimens and DNA sequence data for D. obtusa.

Persistence of Buggy Creek virus (Togaviridae, Alphavirus) for two years in unfed swallow bugs (Hemiptera: Cimicidae: Oeciacus vicarius).

Alphaviruses (Togaviridae) have rarely been found to persist for long in the adult insects that serve as their vectors. The ectoparasitic swallow bug (Hemiptera: Cimicidae: Oeciacus vicarius Horvath), the vector for Buggy Creek virus (BCRV; Togaviridae, Alphavirus), lives year-round in the mud nests of its host, the cliff swallow (Petrochelidon pyrrhonota Vieillot). We measured the prevalence of BCRV in swallow bugs at sites with cliff swallows present and at the same sites after cliff swallows had been absent for 2 yr. We collected bugs directly from cliff swallow nests in the field and screened bug pools with BCRV-specific real-time-polymerase chain reaction (RT-PCR) and plaque assay. At two colony sites last occupied by birds 2 yr earlier, we found 12.5 and 55.6% of bug pools positive for BCRV RNA by RT-PCR. Infection rates (per 1,000 bugs) for these sites were 1.32 and 7.39. RNA prevalence in the unfed bugs was not significantly different from that in fed bugs 2 yr earlier at the same sites. The RNA-positive samples from unfed bugs failed to yield cytopathic BCRV by Vero-cell plaque assay. However, viral RNA concentrations did not differ between unfed bugs and bugs at active sites, and over 84% of positive bug pools were cytopathic to Vero cells 4-5 wk later, after cliff swallows moved into one of the colony sites. These data demonstrate the persistence of potentially infectious BCRV in unfed swallow bugs for at least 2 yr in nature.

Detection of spotted fever group Rickettsia spp. from bird ticks in the U.K.

Migratory birds are known to play a role in the long-distance transportation of microorganisms. To investigate whether this is true for rickettsial agents, we undertook a study to characterize tick infestation in populations of the migratory passerine bird Riparia riparia (Passeriformes: Hirundinidae), the sand martin. A total of 194 birds were sampled and ticks removed from infested birds. The ticks were identified as female Ixodes lividus (Acari: Ixodidae) using standard morphological and molecular techniques. Tick DNA was assayed to detect Rickettsia spp. using polymerase chain reaction and DNA was sequenced for species identification. A single Rickettsia spp. was detected in 100% of the ticks and was designated Rickettsia sp. IXLI1. Partial sequences of 17-kDa and ompA genes showed greatest similarity to Rickettsia sp. TCM1, an aetiological agent of Japanese spotted fever-like illness, previously described in Thailand. Phylogenetic analysis showed that Rickettsia sp. IXLI1 fitted neatly into a group containing strains Rickettsia japonica, Rickettsia sp. strain Davousti and Rickettsia heilongjiangensis. In conclusion, this research shows that U.K. migratory passerine birds host ticks infected with Rickettsia species and contribute to the geographic distribution of spotted fever rickettsial agents.

Divergent sexual signals reflect costs of local parasites.

Many closely related populations are distinguished by variation in sexual signals and this variation is hypothesized to play an important role in reproductive isolation and speciation. Within populations, there is considerable evidence that sexual signals provide information about the incidence and severity of parasite infections, but it remains unclear if variation in parasite communities across space could play a role in initiating or maintaining sexual trait divergence. To test for variation in parasite-associated selection, we compared three barn swallow subspecies with divergent sexual signals. We found that parasite community structure and host tolerance to ecologically similar parasites varied between subspecies. Across subspecies we also found that different parasites were costly in terms of male survival and reproductive success. For each subspecies, the preferred sexual signal(s) were associated with the most costly local parasite(s), indicating that divergent signals are providing relevant information to females about local parasite communities. Across subspecies, the same traits were often associated with different parasites, indicating that parasite-sexual signal links are quite flexible and may evolve relatively quickly. This study provides evidence for (1) variation in parasite communities and (2) different parasite-sexual signal links among three closely related subspecies with divergent sexual signal traits, suggesting that parasites may play an important role in initiating and/or maintaining the divergence of sexual signals among these closely related, yet geographically isolated populations.

Molecular characterization of swallow haemoproteids, with description of one new Haemoproteus species.

Haemoproteus species (Haemosporida, Haemoproteidae) are cosmopolitan bird blood parasites, which often cause relatively benign infections in adapted avian hosts, but severe and even lethal haemoproteosis might develop due to internal organ damage if these pathogens inhabit non-adapted (wrong) hosts. Haemoproteids of swallows (Hirundinidae) remain fragmentarily investigated, with only two haemoproteid species reported in this bird family, which members are cosmopolitan, diverse and inhabit various terrestrial ecosystems, particularly in tropical countries. This study describes and provides molecular characterization of Haemoproteus parahirundinis n. sp. (cytochrome b lineage hHIRUS05), parasite of the most broadly distributed swallow, the Barn swallow Hirundo rustica. Gametocytes, gametes and ookinetes of the new species were examined and compared with other haemoproteids described in swallows. The phylogenetic analysis indicated the existence of a largely undescribed Haemoproteus species diversity in birds of the Hirundinidae and also suggests that all lineages of haemoproteids reported in swallows are transmitted by Culicoides biting midges, but not louse flies of the Hippoboscidae, which often inhabit their nests. The biting midges should be the first targets in vectors research of swallow haemoproteids. This study indicates existence of Haemoproteus species, which are readily distinct based on morphological characters of their blood and sporogonic stages, but differ only negligently in partial cytochrome b sequences, the main markers broadly used in molecular characterization of haemoproteids. That calls for further taxonomic research on haemoproteid in swallows, many species of which are endangered or even threatened with extinction because of habitat degradation.

Isolation of Buggy Creek virus (Togaviridae: Alphavirus) from field-collected eggs of Oeciacus vicarius (Hemiptera: Cimicidae).

Alphaviruses (Togaviridae) rarely have been found to be vertically transmitted from female arthropods to their progeny. We report two isolations of Buggy Creek virus (BCRV), an ecologically unusual alphavirus related to western equine encephalomyelitis virus, from field-collected eggs of cimicid swallow bugs (Oeciacus vicarius Horvath), the principal vector for BCRV. Ten percent of egg pools were positive for BCRV, and we estimated minimum infection rates to be 1.03 infected eggs per 1,000 tested. The results show potential vertical transmission of BCRV, represent one of the few isolations of any alphavirus from eggs or larvae of insects in the field, and are the first report of any virus in the eggs of cimicid bedbugs. The specialized ecological niche of BCRV in swallow bugs and at cliff swallow (Petrochelidon pyrrhonota Vieillot) nesting sites may promote vertical transmission of this virus.

Overwintering of infectious Buggy Creek virus (Togaviridae: Alphavirus) in Oeciacus vicarius (Hemiptera: Cimicidae) in North Dakota.

Arboviruses have seldom been found overwintering in adult vectors at northern latitudes in North America. Buggy Creek virus (BCRV; Togaviridae, Alphavirus) is an ecologically unusual arbovirus vectored principally by the cimicid swallow bug (Oeciacus vicarius Horvath). The ectoparasitic bugs reside year-round in the mud nests of their host, the cliff swallow (Petrochelidon pyrrhonota Vieillot). We report successful overwintering of infectious BCRV in bugs at a field site in western North Dakota, where mid-winter temperatures routinely reach -11 to -15 degrees C. Approximately 21% of bug pools were positive for virus in early spring just before the cliff swallows' return to their nesting colonies; this proportion did not differ significantly from that in summer at active cliff swallow nesting colonies in the same study area. Fewer of the isolates in early spring were cytopathic on Vero cells, and those that were infectious showed less plaque formation than did summer samples. The results show that infectious BCRV commonly overwinters in the adult stages of its vector at northern latitudes in North America.

A New Eimerian (Apicomplexa: Eimeriidae) from the Barn Swallow, Hirundo rustica (Aves: Passeriformes: Hirundinidae), in Southeastern Oklahoma: The Fourth Eimerian Species from New World Passeriformes.

Barn swallows (Hirundo rustica) are the most widespread swallow species in the world. However, little is known about the coccidian parasites of H. rustica. Feces from a single H. rustica nesting in McCurtain County, Oklahoma, were collected in May 2018 and examined for coccidia; the swallow was found to be passing a new species of Eimeria. Oocysts of Eimeria hochatownensis n. sp. are ellipsoidal with a smooth bi-layered wall, measure (L × W) 25.5 × 15.2 µm, and have a length/width (L/W) ratio of 1.7; a micropyle and oocyst residuum are absent, but polar granule(s) are present. Sporocysts are ellipsoidal and measure 12.8 × 6.5 µm, L/W 2.0; a nipple-like Stieda body is present, but sub-Stieda bodies and para-Stieda bodies are absent. The sporocyst residuum is composed of a compact spheroid with a dense, irregular mass of finer granules lying between and dispersed among the sporozoites. This is the first eimerian reported from H. rustica and the family Hirundinidae, and only the fourth Eimeria spp. known from passerine birds of the New World.

Ecological correlates of buggy creek virus infection in Oeciacus vicarius, southwestern Nebraska, 2004.

Buggy Creek virus (family Togaviridae, genus Alphavirus, BCRV) is an alphavirus within the western equine encephalitis virus complex whose primary vector is the swallow bug, Oeciacus vicarius Horvath (Hemiptera: Cimicidae), an ectoparasite of the colonially nesting cliff swallow, Petrochelidon pyrrhonota, that is also a frequent host for the virus. We investigated ecological correlates of BCRV infection in 100-bug pools at 14 different swallow colony sites in southwestern Nebraska from summer 2004, by using plaque assay on Vero cells to identify cytopathic virus and reverse transcription-polymerase chain reaction to identify noncytopathic viral RNA. We found 26.7% of swallow bug pools positive for BCRV, with 15.6% showing cytopathic ("infectious") virus and 11.0% noncytopathic ("noninfectious") viral RNA. The prevalence of cytopathic BCRV increased with cliff swallow colony size in the current year; the percentage of noncytopathic samples at a site did not vary with colony size in the current year but increased with the previous year's colony size at a site. Active colony sites (those used by swallows) had higher percentages of cytopathic BCRV in bug pools than at inactive colony sites, but the reverse held for noncytopathic viral RNA. Nests that were occupied by birds at some time in the season had more pools with cytopathic BCRV than did inactive nests. Colonies used by birds for the first or second time had less virus in bugs than did sites that had had a longer history of bird use. The percentage of pools with BCRV was affected by whether bugs were clustering at nest entrances or distributed elsewhere on a nest. The prevalence of cytopathic samples decreased at inactive colony sites and increased at active sites over the course of the summer, whereas the reverse pattern held for noncytopathic samples. Noncytopathic bug pools seem to reflect infection patterns from a previous year. The results suggest that the birds play an important role in amplification of the virus and that the spatial foci of BCRV occurrence can be predicted based on characteristics of cliff swallow colonies and the cimicid bugs that are associated with them.

Tree swallows (Tachycineta bicolor) nesting on wetlands impacted by oil sands mining are highly parasitized by the bird blow fly Protocalliphora spp.

Oil sands mining is steadily expanding in Alberta, Canada. Major companies are planning reclamation strategies for mine tailings, in which wetlands will be used for the bioremediation of water and sediments contaminated with polycyclic aromatic hydrocarbons and naphthenic acids during the extraction process. A series of experimental wetlands were built on companies' leases to assess the feasibility of this approach, and tree swallows (Tachycineta bicolor) were designated as upper trophic biological sentinels. From May to July 2004, prevalence and intensity of infestation with bird blow flies Protocalliphora spp. (Diptera: Calliphoridae) were measured in nests on oil sands reclaimed wetlands and compared with those on a reference site. Nestling growth and survival also were monitored. Prevalence of infestation was surprisingly high for a small cavity nester; 100% of the 38 nests examined were infested. Nests on wetlands containing oil sands waste materials harbored on average from 60% to 72% more blow fly larvae than those on the reference site. Nestlings on reclaimed sites suffered mean parasitic burdens about twice that of those on the reference site; and for comparable parasitic load, they exhibited greater pathologic effects (e.g., decreased body mass) than control nestlings. The heavy blow fly infestation on oil sands-impacted wetlands suggests that oil sands mining disturbs several components of the local ecosystem, including habitat characteristics, blow fly predators, and host resistance to parasites.