Search

As the climate changes, global systems have become increasingly unstable and unpredictable. This is particularly true for many disease systems, including subtypes of highly pathogenic avian influenzas (HPAIs) that are circulating the world. Ecological patterns once thought stable are changing, bringing new populations and organisms into contact with one another. Wild birds continue to be hosts and reservoirs for numerous zoonotic pathogens, and strains of HPAI and other pathogens have been introduced into new regions via migrating birds and transboundary trade of wild birds. With these expanding environmental changes, it is even more crucial that regions or counties that previously did not have surveillance programs develop the appropriate skills to sample wild birds and add to the understanding of pathogens in migratory and breeding birds through research. For example, little is known about wild bird infectious diseases and migration along the Mediterranean and Black Sea Flyway (MBSF), which connects Europe, Asia, and Africa. Focusing on avian influenza and the microbiome in migratory wild birds along the MBSF, this project seeks to understand the determinants of transboundary disease propagation and coinfection in regions that are connected by this flyway. Through the creation of a threat reduction network for avian diseases (Avian Zoonotic Disease Network, AZDN) in three countries along the MBSF (Georgia, Ukraine, and Jordan), this project is strengthening capacities for disease diagnostics; microbiomes; ecoimmunology; field biosafety; proper wildlife capture and handling; experimental design; statistical analysis; and vector sampling and biology. Here, we cover what is required to build a wild bird infectious disease research and surveillance program, which includes learning skills in proper bird capture and handling; biosafety and biosecurity; permits; next generation sequencing; leading-edge bioinformatics and statistical analyses; and vector and environmental sampling. Creating connected networks for avian influenzas and other pathogen surveillance will increase coordination and strengthen biosurveillance globally in wild birds. [ABSTRACT FROM AUTHOR]

The primary cue for initiation of spring migratory restlessness ( Zugunruhe) in landbird migrants is photoperiod. Gonadal hormones are known to have a role in the regulation of migratory disposition; however, the extent of their effect is not well understood. We examined the impact of exogenous testosterone on the onset of migratory restlessness in gray catbirds ( Dumetella carolinensis). Catbirds were stratified by sex and randomly assigned to two rooms; individuals in one room were photoadvanced to initiate migratory restlessness and the other room was maintained on a 12:12 light/dark photoperiod. Each room had three groups ( n = 10/group); males with testosterone implants, males with empty implants, and females. We predicted that in the photoadvanced room males with testosterone implants would initiate migratory activity earlier than empty-implanted males. We found that in the photoadvanced group, testosterone-implanted males initiated migration 2 weeks prior to empty-implanted males, and 3 weeks prior to females. In the non-photoadvanced males, the testosterone-implanted males initiated migration at the same time as the corresponding group in the photoadvanced room, while the empty-implanted males and females did not exhibit Zugunruhe. Our results illustrate that elevated testosterone can advance the onset of Zugunruhe, even in the absence of an extended photoperiod. Additionally, the onset of migratory restlessness observed in the photoadvanced, non-testosterone-implanted males and females further supports the importance of photoperiod as a cue for migratory restlessness. An interesting observation was the intersexual differences in the onset of migratory activity in gray catbirds, a species not previously known to exhibit protandry. [ABSTRACT FROM AUTHOR]

1. Glucocorticoid hormones are an integral part of the vertebrate stress response, and theoretical models argue for a link between glucocorticoid levels and individual fitness. The cort-fitness hypothesis posits that elevated levels of baseline glucocorticoids are reflective of an individual in poor condition and with a reduced likelihood of survival. Surprisingly, this hypothesis remains virtually untested for the juvenile life-history stage, a period that is often characterized by high mortality rates. 2. To address this issue, we explored whether glucocorticoid levels just prior to fledging were related to survival during the juvenile period in the Swainson's thrush ( Catharus ustulatus), a short-lived, temperate-breeding passerine bird. Over 2 years, we blood-sampled nestling thrushes to quantify glucocorticoid levels and then used radio telemetry to assess whether individuals died or survived to emigrate from the study area. Finally, we measured vegetation characteristics at the nest and at locations used by individuals during the juvenile period to quantify the relative importance of habitat features and glucocorticoid levels on survival. 3. Predation was the leading cause of death, and overall juvenile survival rate was 34·6%. We found that survival was positively associated with baseline corticosterone and, to a lesser extent, size-corrected body mass and date of fledging. Contrary to expectations, we found no evidence that the amount of vegetative cover at the nest site or at locations used during the juvenile period was associated with survival. 5. Although we cannot completely rule out the cort-fitness hypothesis, our data appear to support the cort-activity hypothesis and suggest that elevated baseline corticosterone levels in juvenile thrushes may be linked to enhanced post-fledging survival via increased locomotor activity that promotes foraging, more effective escape from predators or both. [ABSTRACT FROM AUTHOR]

Migration is a physiologically demanding activity. Recent studies suggest that migrating birds can improve their immune and antioxidant status during stopover, implying that variation in stopover habitat can affect migrants' health. We studied 2 species that are strongly frugivorous during fall migration, Swainson's Thrushes (Catharus ustulatus) and Gray Catbirds (Dumetella carolinensis). We asked whether birds that used shrubland dominated by exotic plants experienced differences in mass change, immune function, and antioxidant status relative to conspecifics in native-dominated shrubland during fall stopover in Michigan, USA, in 2012-2013. We found no habitat-related differences in any of the measured health parameters for Swainson's Thrushes. However, Gray Catbirds using nativedominated shrubland retained mass while those in exotic-dominated shrubland lost mass in 2013. Gray Catbirds in exotic-dominated habitat that year also had poorer immune status (elevated granulocyte:lymphocyte ratio and reduced hemagglutination and haptoglobin) and had lower plasma total carotenoids (immunostimulatory antioxidants) relative to conspecifics in native-dominated shrubland. While these findings were not replicated in 2012, circulating antioxidant capacity was lower in both years in Gray Catbirds captured in exotic habitat. Habitatspecific estimates of dietary energy, carotenoid, and antioxidant content per unit mass of fruit were similar between habitat types for Swainson's Thrushes. For Gray Catbirds, however, the fruit diet was lower in carotenoids and antioxidant capacity, but not in energy, in exotic habitat. Our results provide evidence that differential use of stopover habitats may affect the immune and antioxidant status of migrating landbirds. Furthermore, our results suggest that habitat may affect health status based on the complex relationships among quality and abundance of food, food preferences, and refueling performance, which vary among species. We suggest that future studies measure immune and antioxidant metrics in addition to refueling performance to better understand the effects of stopover habitat use on landbird migrant health. This information may improve assessment of habitat quality for migrants. [ABSTRACT FROM AUTHOR]

The ability to locate high-quality stopover habitat has fitness implications for migrating landbirds, and alteration of stopover habitats due to human land-use change, including the introduction of nonnative plants, has been identified as a conservation concern. We tested whether the use and selection of shrublands dominated by exotic plants differed from that of native-dominated shrublands. Specifically, we compared capture rates, transfer rates between habitats, within-foraging-range habitat selection, and food items of Swainson's Thrushes (Catharus ustulatus) and Gray Catbirds (Dumetella carolinensis) between exotic- and native-dominated shrublands in Michigan, USA, during fall migration of 2012 and 2013. Capture rates were >20% higher for thrushes and >250% higher for catbirds in native shrubland. Capture--recapture data showed that birds moved from exotic to native shrubland at higher rates than vice versa. For radio-tagged thrushes and catbirds, native shrubland was ~30% more likely to be used than expected by land cover at the within-foraging-range scale. Thrushes, but not catbirds, avoided exotic shrubs within their foraging ranges. Native Lindera benzoin fruit was >50% more likely to be found in fecal samples from both bird species in native-dominated shrubland than in exotic-dominated shrubland, and was the predominant food item in the former habitat type. Collectively, our results suggest that fall migrating Swainson's Thrushes and Gray Catbirds select, and hence occur at higher densities in, predominantly native shrublands rather than exotic-dominated shrublands. One mechanism for this pattern may be their preference for certain native fruits, such as L. benzoin. Our results suggest that native shrubland may be an especially important stopover habitat for frugivorous birds during fall migration. [ABSTRACT FROM AUTHOR]