Effects of Parental and Direct Methylmercury Exposure on Flight Activity in Young Homing Pigeons (Columba livia)

Abstract

Mercury is one of the most common metals found in contaminated ecosystems. It occurs naturally, but high levels found in contaminated areas derive from human use practices. Among the most vulnerable species to exposure are birds that live, nest, or feed in or near these contaminated ecosystems. Because of the known neurological effects of mercury on birds, it is hypothesized that effects upon migratory ability would be evident after exposure to low levels of this metal, and effects may be exacerbated in young birds. Difficulties in following mercury exposed birds once they migrate away from contaminated areas have left investigators with insufficient data to establish exposure levels causing injury of migratory species due to migration disruption. Breeding pigeons were exposed to ~1.0 mg/kg/day methylmercury via the drinking water, and first round offspring were trained to home after fledging, while also continually exposed to methylmercury. The young pigeons were released individually for three flights, and flight times were assessed and compared to control young pigeon flight times from 3.5, 9, 21, 53, 65, and 98 air miles as well as two individual flights at ~50 air miles from multiple directions. Results indicate that methylmercury exposed birds exhibit slower flight times than controls during the initial flight, and generally improve on successive flights at each distance and direction. This may suggest orientation impairment and allude to migration disruption in migratory species.

High-precision isotopic analysis sheds new light on mercury metabolism in long-finned pilot whales (Globicephala melas)

“…During migration, the birds lost an important amount of muscle, inducing a mobilization of MeHg stored in this tissue. The mobilized MeHg can be transported via the bloodstream to vital organs, such as brain, where it can cause neurological damage that has hypothetically been identified as the origin of loss of orientation while traveling long distances 52,53 . Next to the redistribution of Hg from contaminated vital organs in adult whales, an increase in the level of MeHg demethylation (assuming preferential demethylation of the lighter Hg isotopes) into less toxic iHg species, e.g ., under the form of HgSe particles that remain in the muscle tissue, together with the mobilization of MeHg, may explain both the reduction of the MeHg fraction and the lighter bulk Hg isotopic composition of muscle tissues for the oldest whales.

Figure 3δ 202 Hg (black – left y-axis) and MeHg fraction (% MeHg, red – right y-axis) obtained for muscle ( A ) and liver ( B ) as a function of age.

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Evidence of negative seasonal carry‐over effects of breeding ground mercury exposure on survival of migratory songbirds

“…The blackpoll warbler is an exceptional migrant that undertakes non-stop, multi-day flights over the Atlantic Ocean to reach wintering areas in South America (DeLuca et al 2015). As a neurotoxin, Hg may impair their navigation (Moye et al 2016), flight performance (Ma et al 2018), and foraging ability (Kobiela et al 2015). Thus, it is reasonable to posit that Hg burden may contribute to reduced survival during migration and winter for this species.…”

“…Methylmercury has been demonstrated to impair bird immune function (Hawley et al 2009, Lewis et al 2013), foraging behavior (Kobiela et al 2015), navigation (Moye et al 2016), and flight ability (Carlson et al 2014, Ma et al 2018, which could be particularly detrimental during long-distance migration. In this study, we used songbird feathers grown prior to autumn migration to examine the link between Hg exposure at breeding grounds and songbird survival until the subsequent spring return migration (a seasonal carry-over effect).…”

Reprint of: Overview of avian toxicity studies for the Deepwater Horizon Natural Resource Damage Assessment

“…The rock pigeon, although not a water-based bird such as those exposed to oil in the DWH spill, is a useful model to study the effects of oil exposure on flight dynamics and the metabolic challenges of migratory flight. The rock pigeon has been used to assess the effects of other toxicants on flight activity (Moye et al, 2016).…”