Mercury Exposure Is Associated with Urbanization but not Salmonella Status in White Ibis (Eudocimus albus).

Mercury (Hg) is a ubiquitous contaminant in wetlands that can cause immunosuppression in birds, which may increase susceptibility to colonization with Salmonella spp. Previously, we found that White Ibis (Eudocimus albus), a recently urbanized wading bird, shed Salmonella spp. at a higher prevalence when captured at urban sites, compared with natural sites. In this study, we sought to determine if Hg burdens in ibis are related to Salmonella status or degree of urbanization or both. We analyzed feathers from 94 ibis in Palm Beach County, Florida, USA, along an urbanization gradient (0-68% urbanization) and from individuals with confirmed Salmonella spp. status (shedding or not shedding). We detected Hg in all ibis feathers (0.22-8.47 mg/kg; mean=1.96 mg/kg; SD=1.94). The Hg concentration was not significantly correlated to Salmonella spp. shedding status (Wilcoxon rank sum test, W=1170; P=0.596) but was negatively associated with capture site urbanization level (R2=0.327; P=0.026). Our findings may suggest that the immunosuppressive effects of Hg do not affect Salmonella shedding in the ibis or that Hg burdens were too low to affect Salmonella shedding status. Further, ibis that were captured in high urbanization sites appeared to have a lower risk of Hg exposure than ibis that were captured within low urbanization sites.

An Acute Mortality Event Associated with Novel Macrorhabdus ornithogaster Infection and Underlying Factors in a Newly-Established Captive Group of American White Ibis (Eudocimus albus) Nestlings.

Twenty-four American white ibis (Eudocimus albus) nestlings were collected in Florida (USA) on 17 April 2017 to establish a captive flock. On 7 May 2017, three birds died suddenly, following severe lethargy, hemorrhaging from the mouth and nares, anorexia, and production of bright-green colored feces. An additional ibis with delayed growth and pathological fractures was euthanized 18 May 2017. Severe ventriculitis associated with Macrorhabdus ornithogaster was noted in all four birds, bacterial sepsis was confirmed in one bird by culture and histologic examination, and bacterial endotoxemia was suspected in two birds based on gross and histologic examination, but no bacteria were isolated from these birds. Birds also had vitamin E liver levels consistent with coagulopathy previously described in pelicans. We sampled feces from 91 adult, free-living, healthy ibis in Florida in July 2017 and found 71% were shedding organisms with morphologic characteristics consistent with Macrorhabdus sp. Molecular characterization of the ibis-origin M. ornithogaster showed it was phylogenetically related to numerous M. ornithogaster sequences. It is unknown if M. ornithogaster infection resulted in clinical disease as a result of dietary or stress-related dysbiosis, or other factors. Macrorhabdus-associated disease has not previously been confirmed in wading birds. We discuss potential associations of gastric M. ornithogaster infection with morbidity and mortality in these cases and highlight the need for additional studies on this pathogen in free-living birds.

Timing and magnitude of net methylmercury effects on waterbird reproductive output are dependent on food availability.

Mercury (Hg) is a globally distributed pollutant. Its sub-lethal effects on reproduction of birds have been used as indicators of contamination and of potential demographic effects. However, studies typically used single endpoints that might not be representative of entire reproductive cycle. To estimate timing and net cumulative effects of Hg exposure under field conditions, we used observational data over 11 years from >1200 nests of great egrets breeding under temporally and spatially varying food availability and Hg exposures in the Florida Everglades. We collected measures of fish biomass and availability (>100 locations annually) and used four avian reproductive endpoints that represented the entire breeding cycle. We calculated net reproductive loss by adding estimated Hg effects on failures prior to egg laying, clutch size, hatching success and nestling survival in response to food availability and Hg exposure. To validate and assess results of the observational egret study, we ran the same analyses with data of captive breeding white ibises experimentally exposed to Hg with ad libitum food over 3 years. We found large (>50 %) reductions in great egret offspring with high Hg exposure (18 µg/g dw THg nestling feather, ~0.7 µg/g ww whole egg THg) and high food availability, and even larger reductions (up to 100 %) with high Hg exposure and low food. Timing and the relative contribution of different endpoints to overall reproductive failure varied with food availability. Failures prior to egg laying were relevant at all food availabilities and proportionally most important during high food availability (~70 % of total losses). Under high food, post-hatching failures increased moderately with increasing exposure (~10 % of total losses), and under low food, hatching failures became dominant (~50 % of total losses). Patterns of failure of captive white ibis fed ad libitum resembled those of great egrets under high food availability but differed in total magnitude. We suggest that, a) net reproductive effects of Hg in free-ranging animals are probably much higher than generally reported in studies using single endpoints, b) Hg effect sizes vary considerably among different endpoints and c) food availability is a strong driver of timing and net effects of Hg exposure.

West Nile Virus Infections in an Urban Colony of American White Ibises (Eudocimus albus) in South Florida, USA.

West Nile virus (WNV) is pathogenic in a wide range of avian hosts and is endemic in much of North America. This virus is responsible for population declines of some Passeriformes. We describe a WNV-associated mortality event in American White Ibis (Eudocimus albus) nestlings. This is a species, inherent to the Everglades ecosystem, which has recently begun nesting in urban areas. An urban colony in south Florida was monitored from March-July in 2020 as part of an ongoing study. Nestling carcasses were collected opportunistically and sent to the Southeastern Cooperative Wildlife Disease Study, University of Georgia within 24 h for diagnosis. Three ibis nestling deaths were confirmed to be caused by WNV infection based on histopathology, immunohistochemistry, and reverse transcription PCR. Serial plasma samples collected weekly from 36 healthy chicks of the same urban rookery were tested for WNV-neutralizing antibodies via plaque reduction neutralization test; four chicks were seropositive. Antibody titers in three seropositive chicks from which serial samples were collected waned over time, suggesting maternal antibody transfer. Ibis mortalities were consistent with a spike of WNV activity in this region of Florida. West Nile virus infection may be an important seasonal cause of mortality for wading bird nestlings.

Avian Influenza Virus Status and Maternal Antibodies in Nestling White Ibis (Eudocimus albus).

The White Ibis (Eudocimus albus), a nomadic wading bird, has increased its exploitation of urban habitats in South Florida, United States, and has recently established several urban breeding colonies. Certain characteristics of ibis ecology could position them in the natural cycle of the avian influenza virus (AIV). In fact, experimentally infected ibises were shown to be competent hosts for multiple AIV subtypes, and seroconversion to AIV has been documented in adult ibises in natural populations. However, the mechanisms of transmission and the timing of infection are unclear as we have yet to isolate AIV from a free-living ibis. To investigate the age-specific AIV dynamics of ibis, we captured nestlings (n = 115) weekly for 1-4 weeks from urban and natural settings in 2020 and 2021. We collected choanal/cloacal swabs for rRT-PCR and virus isolation, and plasma to screen for maternal AIV antibodies. AIV was not detected in any individual by virus isolation; however, maternal antibodies to AIV were detected in 95% of nestlings, with varying rates of catabolism. These results confirm that nestlings are afforded maternal antibodies from adults at rates reflective of higher adult seroprevalence than previously documented and that nestlings in breeding colonies may have some degree of protection and are unlikely to become infected with AIV.

Site Fidelity is Associated with Food Provisioning and Salmonella in an Urban Wading Bird.

Food provisioning can change wildlife pathogen dynamics by altering host susceptibility via nutrition and/or through shifts in foraging behavior and space use. We used the American white ibis (Eudocimus albus), a wading bird increasingly observed in urban parks, as a model to study synergistic relationships between food provisioning and infection risk across an urban gradient in South Florida. We tested whether Salmonella prevalence was associated with changes in ibis diet (stable isotope analysis), space use (site fidelity via GPS tracking), and local density (flock size). We compared the relative importance of these mechanisms by ranking candidate models using logistic regression. We detected Salmonella in 27% of white ibises (n = 233) sampled at 15 sites. Ibises with diets higher in anthropogenic food exhibited higher site fidelity. Salmonella prevalence was higher at sites where ibises exhibited greater site fidelity and Salmonella was more prevalent in soil and water. Overlap in Salmonella serotypes between ibises and soil or water also was more likely at sites where ibises exhibited higher site fidelity. Our results suggest that repeated use of foraging areas may increase Salmonella exposure for birds if foraging areas are contaminated from animal feces, human waste, or other bacterial sources. Limiting wildlife feeding in parks-perhaps best achieved through understanding the motivations for feeding, education, and enforcement-may reduce health risks for wildlife and the public.

Exploring the genetic structure of Parastrigea diovadena Dubois and Macko, 1972 (Digenea: Strigeidae), an endoparasite of the white ibis, Eudocimus albus, from the Neotropical region of Mexico.

Parastrigea diovadena Dubois and Macko, 1972, is an allogenic trematode species that infects the intestine of white ibis. This widely distributed Neotropical species has been studied poorly, and nothing is known about its population genetic structure. In the current study, we attempt to fill this gap for the first time and to explore the genetic diversity in P. diovadena populations from three biogeographic provinces (Sierra Madre Oriental, Sierra Madre Occidental, and Sierra Madre del Sur) in the Neotropical region of Mexico. Newly generated sequences of the internal transcribed spacers (ITS) from ribosomal DNA and cytochrome c oxidase subunit 1 (cox 1) from mitochondrial DNA were compared with sequences available from the GenBank data set. Phylogenetic analyses performed with the ITS and cox 1 data sets using maximum likelihood and Bayesian inference unequivocally showed that new sequences of P. diovadena recovered from the white ibis formed a clade with other sequences of specimens previously identified as P. diovadena. The intraspecific genetic divergence among the isolates was very low, ranging from 0 to 0.38% for ITS and from 0 to 1.5% for cox 1, and in combination with the phylogenetic trees confirmed that the isolates belonged to the same species. The cox 1 haplotype network (star-shaped) inferred with 62 sequences revealed 36 haplotypes. The most frequent haplotype (H3, n = 18) corresponded to specimens from all the populations (except Tecolutla, Veracruz). In addition to the common haplotype, we identified four other shared haplotypes (H2, H9, H12, and H14) and 31 unique haplotypes (singlets). In addition, high haplotype diversity (Hd = 0.913), low nucleotide diversity (Pi = 0.0057), and null genetic differentiation or population structure (Fst = 0.0167) were found among the populations from the three biogeographic provinces. The results suggest that the biology of the definitive host has played a key role in the population genetic structure of Parastrigea diovadena in the Neotropical region of Mexico.

Urban specialization reduces habitat connectivity by a highly mobile wading bird.

BACKGROUND: Mobile animals transport nutrients and propagules across habitats, and are crucial for the functioning of food webs and for ecosystem services. Human activities such as urbanization can alter animal movement behavior, including site fidelity and resource use. Because many urban areas are adjacent to natural sites, mobile animals might connect natural and urban habitats. More generally, understanding animal movement patterns in urban areas can help predict how urban expansion will affect the roles of highly mobile animals in ecological processes. METHODS: Here, we examined movements by a seasonally nomadic wading bird, the American white ibis (Eudocimus albus), in South Florida, USA. White ibis are colonial wading birds that forage on aquatic prey; in recent years, some ibis have shifted their behavior to forage in urban parks, where they are fed by people. We used a spatial network approach to investigate how individual movement patterns influence connectivity between urban and non-urban sites. We built a network of habitat connectivity using GPS tracking data from ibis during their non-breeding season and compared this network to simulated networks that assumed individuals moved indiscriminately with respect to habitat type. RESULTS: We found that the observed network was less connected than the simulated networks, that urban-urban and natural-natural connections were strong, and that individuals using urban sites had the least-variable habitat use. Importantly, the few ibis that used both urban and natural habitats contributed the most to connectivity. CONCLUSIONS: Habitat specialization in urban-acclimated wildlife could reduce the exchange of propagules and nutrients between urban and natural areas, which has consequences both for beneficial effects of connectivity such as gene flow and for detrimental effects such as the spread of contaminants or pathogens.

EXPERIMENTAL INFECTIONS AND SEROLOGY INDICATE THAT AMERICAN WHITE IBIS (EUDOCIUMUS ALBUS) ARE COMPETENT RESERVOIRS FOR TYPE A INFLUENZA VIRUS.

The American White Ibis (Eudocimus albus) is a nomadic wading bird common to wetland habitats in the southeastern US. In south Florida, US, habitat depletion has driven many ibis to become highly urbanized. Although they forage in neighborhood parks, artificial wetlands, backyards, and golf courses, the majority continue to nest in natural wetlands, often in dense, mixed species colonies. Adults and juveniles commonly disperse thousands of kilometers to other breeding colonies along the Gulf and southeast Atlantic coasts, presenting the potential for close contact with humans, domestic animals, and other wild bird species. Historically, wading birds were not considered to be significant hosts for influenza A virus (IAV), yet as ibis regularly move among various human, domestic animal, and wildlife interfaces, their potential to be exposed to or infected with IAV deserves attention. We experimentally challenged wild-caught, captive-reared White Ibis (n=20) with IAV, tested wild White Ibis for IAV, and serologically tested wild White Ibis for antibodies to IAV. White Ibis were highly susceptible to experimental challenge with H6N1 and H11N9 IAVs, with cloacal shedding lasting an average of 6 d. All 13 infected birds seroconverted by 14 d postinfection as determined by microneutralization. In contrast, no birds challenged with H3N8 were infected. We tested 118 swabs and 578 serum samples from White Ibis captured in southeastern Florida for IAV infection and antibodies to IAV, respectively. Although no IAVs were isolated, 70.4% serum samples were antibody positive by blocking enzyme-linked immunosorbent assay (bELISA). Neutralizing antibodies to H1-H12 were detected in 96.0% of a subset of bELISA positive birds (n=196) and 81.0% tested antibody positive to two or more hemagglutinin subtypes, indicating that exposure to multiple IAVs is common. These results provide evidence that White Ibis are susceptible and naturally infected with IAV and may represent a component of the IAV natural reservoir system.

Impacts of Sublethal Mercury Exposure on Birds: A Detailed Review.

Mercury is a ubiquitous environmental contaminant known to accumulate in, and negatively affect, fish-eating and oceanic bird species, and recently demonstrated to impact some terrestrial songbirds to a comparable extent. It can bioaccumulate to concentrations of >1 µg/g in tissues of prey organisms such as fish and insects. At high enough concentrations, exposure to mercury is lethal to birds. However, environmental exposures are usually far below the lethal concentrations established by dosing studies.The objective of this review is to better understand the effects of sublethal exposure to mercury in birds. We restricted our survey of the literature to studies with at least some exposures >5 µg/g. The majority of sublethal effects were subtle and some studies of similar endpoints reached different conclusions. Strong support exists in the literature for the conclusion that mercury exposure reduces reproductive output, compromises immune function, and causes avoidance of high-energy behaviors. For some endpoints, notably certain measures of reproductive success, endocrine and neurological function, and body condition, there is weak or contradictory evidence of adverse effects and further study is required. There was no evidence that environmentally relevant mercury exposure affects longevity, but several of the sublethal effects identified likely do result in fitness reductions that could adversely impact populations. Overall, 72% of field studies and 91% of laboratory studies found evidence of deleterious effects of mercury on some endpoint, and thus we can conclude that mercury is harmful to birds, and the many effects on reproduction indicate that bird population declines may already be resulting from environmental mercury pollution.

Diversity and prevalence of hemoparasites of wading birds in southern Florida, USA.

Relatively few studies on hemoparasites have been conducted on wading birds in the families Ardeidae and Threskiornithidae (order Pelecaniformes), especially in the United States. In this study, we obtained baseline data on the prevalence and genetic diversity of haemosporidian parasites in wading birds opportunistically sampled from southern Florida, USA. We detected blood parasites in White Ibis (Eudocimus albus), Glossy Ibis (Plegadis falcinellus), Green Heron (Butorides virescens), and Roseate Spoonbill (Platalea ajaja) with several novel host-parasite relationships. Infected birds had low parasitemias (average 0.77%, range 0-4%) suggesting that infections were chronic. Despite the low sample sizes for several of our sampled species, these data highlight the diversity of parasites in this understudied group of birds and suggest that additional studies are needed to investigate the potential impacts of these parasites on their health, especially since southern Florida is becoming increasingly urbanized which can alter parasite transmission or host susceptibility.