Search

Invasive species are widely implicated in the decline of songbird populations, potentially via indirect effects such as the restructuring of ecological communities by non-native plants. We used stable isotope analysis to investigate whether ground-foraging, generalist insectivore ovenbirds (Seiurus aurocapilla (Linnaeus, 1766)) shifted diets following invasion by a non-native shrub, Japanese barberry (Berberis thunbergii DC.), in a temperate woodland system in New York, USA where barberry was previously linked to trophic downgrading in the leaf litter arthropod community. Assimilated ovenbird diets were primarily composed of predatory invertebrates followed by sucking herbivores, chewing herbivores, and detritivores. The only notable changes in assimilated ovenbird diets were a modest 14.7% decrease in chewing herbivore contributions and a minor 7.0% increase in sucking herbivore contributions in forest patches with high barberry densities. Our results indicate that the effects of non-native plants on connections between higher trophic levels are context-dependent, and comparisons with other studies suggest that community complexity and time since introduction are key contextual differences that affect the outcome of an invasion. Our results may reflect compensatory shifts in individual foraging effort by ovenbirds, but, in combination with our previous research, provide little evidence that barberry affects ovenbird condition and therefore downstream outcomes. [ABSTRACT FROM AUTHOR]

I examined the relationship between total mercury (THg) and plasma triglyceride (TRIG; an indicator of body mass change) levels in the blood of migrating Northern Waterthrushes (Parkesia noveboracensis (Gmelin, 1789)) to test the hypothesis that mercury has a negative influence on the stopover refueling rates of migratory birds. THg levels averaged 0.42 ppm and ranged 0.09-2.08 ppm. Model selection indicated that THg was not important for explaining variation in TRIG relative to capture time, body mass, and year. Summed model weights also indicated that THg had low relative importance. Capture time appeared alone in the global best model and had the greatest relative importance. Subsets of birds in the 25th and 75th percentiles of THg level did not have different levels of TRIG. THg in most birds was higher than mean blood levels reported for several other long-distance migrants from the same geographic region, but below the lowest blood level recently determined to cause adverse effects (reduced reproductive success) in a passerine (0.7 ppm). Blood THg levels in this study did not seem to affect foraging efficiency or other attributes of Northern Waterthrushes enough to reduce their stopover refueling rate. Research is needed to identify mercury effect levels for neurological, physiological, and behavioral changes that would impair the migration performance of passerine birds. Key words: mercury, songbird, migration, stopover refueling, triglyceride, Parkesia noveboracensis, Northern Waterthrush. J'ai examine le lien entre le mercure total (THg) et les concentrations de triglycerides plasmatiques (TRIG, un indicateur de changement de la masse corporelle) dans le sang de parulines des ruisseaux (Parkesia noveboracensis (Gmelin, 1789)) en migration afin de tester l'hypothese selon laquelle le mercure a une incidence negative sur les taux de ravitaillement durant les haltes des oiseaux migrateurs. Les valeurs de THg allaient de 0,09 a 2,08 ppm pour une moyenne de 0,42 ppm. La selection de modeles indiquait que le THg n'etait pas un facteur explicatif important des variations des concentrations de TRIG en fonction du moment de la capture, de la masse corporelle ou de l'annee. La somme des poids des modeles indiquait egalement une faible importance relative du THg. Le moment de la capture semblait etre la seule variable explicative dans le meilleur modele global et avait la plus grande importance relative. Les concentrations de TRIG des sous-ensembles d'oiseaux des 25e et 75e centiles de la concentration de THg n'etaient pas differentes. La teneur en THg dans la plupart des oiseaux etait superieures aux teneurs signalees pour plusieurs autres especes de grands migrateurs de la meme region geographique, mais plus faibles que la teneur sanguine minimum pouvant causer des effets nefastes (diminution du succes de reproduction) chez des passereaux recemment etablie a 0,7 ppm. Les concentrations sanguines de THg observees dans le cadre de l'etude ne semblaient pas avoir une incidence suffisante sur l'efficacite de la quete de nourriture ou d'autres attributs des parulines des ruisseaux pour causer une diminution du taux de ravitaillement durant les haltes migratoires. Des travaux sont necessaires pour determiner les concentrations de mercure entrainant des changements neurologiques, physiologiques et comportementaux qui reduiraient la performance migratoire des passereaux. [Traduit par la Redaction] Mots-cles: mercure, oiseau chanteur, migration, ravitaillement durant les haltes, triglyceride, Parkesia noveboracensis, paruline des ruisseaux., Introduction There is growing concern that passerine birds (songbirds) that primarily feed on insects, arachnids, and other macroinvertebrates are accumulating harmful levels of mercury (Seewagen 2010; Evers et al. 2012). [...]

Anthropogenic emissions of mercury have doubled over the past two centuries. Mercury is a dangerous neurotoxin that threatens human health and fish and wildlife populations. The effects of mercury on birds have been relatively well-studied in the laboratory and in nature. Several aspects of neurology, physiology, behaviour, and reproduction have been shown to be adversely affected. Many studies have documented ataxia, lethargy, reduced appetite, reduced egg production, poor hatching success, and aberrant parental care in birds exposed to mercury.The majority of the research done to date, however, has been focused on select taxa (waterbirds), trophic levels (piscivores), habitat types (aquatic systems), geographic regions (North America and Europe), and life history stages (reproduction), leaving the assessment of mercury's threats to birds incomplete. Successful bird conservation strategies are dependent on a comprehensive understanding of the threats facing populations. Here, I discuss the significant knowledge gaps that remain and subsequently suggest priorities for future mercury research in birds. Studies of mercury in terrestrial, insectivorous, and/or passerine species, and how mercury affects migration are especially recommended to fill gaps in our present understanding. [ABSTRACT FROM PUBLISHER]