Mercury toxicity risk and corticosterone levels across the breeding range of the Yellow-breasted Chat

Kristen Mancuso,John D Alexander,Karen E Hodges,John E Elliott,Michelle Zanuttig,Manuel Grosselet,Christine A Bishop

doi:10.1007/s10646-021-02510-6

Abstract

Mercury (Hg) is an environmental contaminant that can negatively impact human and wildlife health. For songbirds, Hg risk may be elevated near riparian habitats due to the transfer of methylmercury (MeHg) from aquatic to terrestrial food webs. We measured Hg levels in tail feathers sampled across the breeding range of the Yellow-breasted Chat (Icteria virens), a riparian songbird species of conservation concern. We assessed the risk of Hg toxicity based on published benchmarks. Simultaneously, we measured corticosterone, a hormone implicated in the stress response system, released via the hypothalamus-pituitary-adrenal axis. To better understand range-wide trends in Hg and corticosterone, we examined whether age, sex, subspecies, or range position were important predictors. Lastly, we examined whether Hg and corticosterone were correlated. Hg levels in chats were relatively low: 0.30 ± 0.02 µg/g dry weight. 148 out of 150 (98.6%) had Hg levels considered background, and 2 (1.6%) had levels considered low toxicity risk. Hg levels were similar between sexes and subspecies. Younger chats (<1 year) had higher Hg levels than older chats (>1 year). Hg levels were lowest in the northern and central portion of the eastern subspecies’ range. Corticosterone concentrations in feathers averaged 3.68 ± 0.23 pg/mm. Corticosterone levels were similar between ages and sexes. Western chats had higher levels of corticosterone than eastern chats. Hg and corticosterone were not correlated, suggesting these low Hg burdens did not affect the activity of the hypothalamus-pituitary-adrenal axis. Altogether, the chat has low Hg toxicity risk across its breeding range, despite living in riparian habitats.

Highlights

Mercury (Hg) is an environmental contaminant of concern to wildlife and humans because it can negatively affect reproduction, neurology, immunology, and behaviour
Two chats (1.3%) were in the low Hg toxicity risk category of 0.2–1 μg/g, one of which originated from the Oregon I study area, and the other in the southwestern region (δ2Hf: −30 < −40‰, Appendix 1)
We examined Hg concentrations in chats across their breeding range and found no evidence that this species is at risk of Hg toxicity despite their affinity for riparian habitats

Summary

Methods

We sampled chats in seven study areas. Four areas were known breeding locations in British Columbia, Canada, and California and Oregon, USA (Table 1, Fig. 1). The remaining three study areas were in Mexico in Nayarit, Chiapas, and Veracruz, where chats were sampled during migration and the non-breeding period. The British Columbia study area was along the channelized South Okanagan River (McKibbin and Bishop 2010). The Nayarit study area consisted of openings and edges of semi-deciduous tropical forests. The Chiapas study site was located within the La Encrujijada Biosphere Reserve near the Pacific Ocean within a large open wetland surrounded by small patches of trees and tall grasses. The Veracruz, Mexico study site was adjacent to a wetland area and surrounded by shrubs and short trees (Gahbauer et al 2016)

Results

Discussion

Conclusion