An ideal technology for non-invasive analysis of body composition should provide highly precise and accurate direct measurements of fat, lean mass and total water of non-anaesthetized subjects within minutes. We validate a quantitative magnetic resonance (QMR) body composition analyzer for birds using House Sparrows (Passer domesticus), European Starlings (Sturnus vulgaris), and Zebra Finches (Taeniopygia guttata). Subjects were scanned awake for three replicate scans of 1.5-3.5 min, and results were compared to gravimetric chemical analysis. Coefficients of variation were B3% for dry fat, wet lean mass and total water. Accuracy of the raw QMR data for fat and total water were high (relative errors B±12.5 and B±4%, respectively), but wet lean mass was significantly biased because QMR does not detect structural tissues. Calibration against gravimetric chemical analysis removed bias and improved accuracy; relative errors were ±6-11% for fat, ±1-2% for wet lean mass, and ±2-4% for total water. QMR is field-portable when transported in a temperature-controlled trailer, and can be used to study fuel storage and body composition dynamics during migration, reproduction, nestling growth, or wintering. In the laboratory, QMR can be used for longitudinal studies of birds under photoperiod, endocrine or other manipulations. Measurements taken before and after metabolic challenges, such as flight in a wind tunnel, make it possible to calculate energy costs, fuel selection and changes in hydration. QMR should find wide application in field and laboratory studies.

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SummaryAnthropogenic 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.

Mercury is a global pollutant that has been widely shown to adversely affect reproduction and other endpoints related to fitness and health in birds, but almost nothing is known about its effects on migration relative to other life cycle processes. Here I consider the physiological and histological effects that mercury is known to have on non-migrating birds and non-avian vertebrates to identify potential mechanisms by which mercury might hinder migration performance. I posit that the broad ability of mercury to inactivate enzymes and compromise the function of other proteins is a single mechanism by which mercury has strong potential to disrupt many of the physiological processes that make long-distance migration possible. In just this way alone, there is reason to expect mercury to interfere with navigation, flight endurance, oxidative balance, and stopover refueling. Navigation and flight could be further affected by neurotoxic effects of mercury on the brain regions that process geomagnetic information from the visual system and control biomechanics, respectively. Interference with photochemical reactions in the retina and decreases in scotopic vision sensitivity caused by mercury also have the potential to disrupt visual-based magnetic navigation. Finally, migration performance and possibly survival might be limited by the immunosuppressive effects of mercury on birds at a time when exposure to novel pathogens and parasites is great. I conclude that mercury pollution is likely to be further challenging what is already often the most difficult and perilous phase of a migratory bird's annual cycle, potentially contributing to global declines in migratory bird populations.