User:Rdflamenco/Effects of contaminants on bird migration

Bird Migration
Migration is an important life history event that allows birds to find abundant food sources as well as shelter from winter weather. There are various anthropogenic factors that imperil these mass movements. Contaminants are one such factor that can impact migration both directly and indirectly. Direct effects, such as mortality and sublethal effects are the most well studied and understood. Indirect effects, such as decreased prey at stopover sites are not completely understood.

Polycyclic aromatic hydrocarbons (PAHs)
Environmentally relevant, sublethal concentrations of polycyclic aromatic hydrocarbons (PAHs) were shown to impair fueling ability in Sanderling (Calidris alba). Cytochrome P450 activity was measured using the biomarker ethoxyresorufin-O-deethylase. Fat deposition, fatty acid and overall energy metabolism were impaired, resulting in decreased body mass gain as well as inefficient use of energy reserves. High detected levels of creatine kinase also indicated muscle damage, which would require a delay in migration to allow time to repair.

Lead
In northern Canada, common eider ducks (Somateria mollissima) that arrived at their breeding grounds later with lower body conditions had higher blood lead concentrations. Exposure to lead has been shown to increase oxidative stress and immune function, which are important factors when considering body condition. Similar results have been found with whooper swans (Cygnus cygnus) in the United Kingom.

Mercury
Dietary methylmurcury (MeHg) resulted in a weaker takeoff flight performance in European starling (Sturnus vulagris) which would put exposed birds at greater risk of predation. Dosed starlings also experienced an acceleration of molting, which resulted in poor feather quality and noticeable gaps, potentially causing of the weakened takeoffs. Poor-quality feathers are known to negatively impact starling flight performance and thermoregulation. Yellow-rumped warblers (Setophaga coronata) exposed to MeHg experienced dose-dependent flight duration decreases, unable to complete a 2-hour flight because of increased frequency of landing or loss of control mid-flight. MeHg exposure in zebra finches (Taeniopygia guttata) increased their basal metabolic rate, decreased peak metabolic rate, and decreased their respiratory quotient. As a known neurotoxin and oxygen antagonist, there are various mechanisms that could be responsible for these sublethal impacts on processes important to migration.

Polychlorinated biphenyls (PCBs)
Aroclor 1254, a PCB mixture, increased Zugunruhe, migratory restlessness, in European starling (Sturnus vulgaris), which would result in an earlier migration departure. Molting was also delayed in male birds, while all dosed birds experienced incorrect directional orientation in an Emlen funnel experiment. Early arriving migrants, which are usually the most fit, tend to mate more than late arrivals, greatly increasing their reproductive success. With an influx of less fit, PCB contaminated individuals, the overall population fitness would decrease.

Pesticides
In a flight time experiment homing pigeons (Columba livia) were exposed to environmentally relevant, sublethal doses of carbofuran, an insecticide that has led to mortality in non-target avian species. Flight times for a 200 mile flight significantly increased four-fold for the group dosed with 0.5 and 1 mg/kg (ppm) carbofuran. Exposure to chlorpyrifos and aldicarb also led to slower flight times in homing pigeons. Additional effects on migration of pesticide exposure and subsequent cholinesterase inhibition include susceptibility to predators and decreased food consumption. White-crowned sparrows (Zonotrichia leucophrys) dosed with p,p'-DDT experienced a decrease in flight time. In addition to decreased flight times, the interaction between dose, flight, and fasting resulted in higher brain concentrations of p,p'-DDT,.

Conservation efforts
Bill Clinton's executive order 13186 directs governmental departments and agencies to continue and further the implementation of the Migratory Bird Treaty Act of 1918 and promotes research and information exchange in regards to the effects of contaminants on migratory birds.