Physiological condition of juvenile wading birds in relation to multiple landscape stressors in the Florida Everglades: effects of hydrology, prey availability, and mercury bioaccumulation.

Garth Herring,Collin A Eagles-Smith,James M Beerens,Dale E Gawlik,Joshua T Ackerman

doi:10.1371/journal.pone.0106447

Garth Herring, Collin A Eagles-Smith + Show 3 more

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https://doi.org/10.1371/journal.pone.0106447

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Abstract

The physiological condition of juvenile birds can be influenced by multiple ecological stressors, and few studies have concurrently considered the effects of environmental contaminants in combination with ecological attributes that can influence foraging conditions and prey availability. Using three temporally distinct indices of physiological condition, we compared the physiological response of nestling great egrets (Ardea alba) and white ibises (Eudocimus albus) to changing prey availability, hydrology (water depth, recession rate), and mercury exposure in the Florida Everglades. We found that the physiological response of chicks varied between species and among environmental variables. Chick body condition (short-term index) and fecal corticosterone levels (medium-term) were influenced by wetland water depth, prey availability, region, and age, but not by mercury contamination. However, mercury exposure did influence heat shock protein 70 (HSP70) in egret chicks, indicating a longer-term physiological response to contamination. Our results indicate that the physiological condition of egret and ibis chicks were influenced by several environmental stressors, and the time frame of the effect may depend on the specialized foraging behavior of the adults provisioning the chicks.

Highlights

Environmental stressors, such as contaminants, prey availability, and adverse weather, can elicit strong physiological responses from wild birds in order to help them overcome short-term challenges
Chick body condition index Egret chick body condition was influenced by water depth (F1, 128.8 = 6.60, P = 0.01), but not region (F2, 114.7 = 2.30, P = 0.10), water recession rate (F1, 119.2 = 2.28, P = 0.14), prey biomass (F1, 142.7 = 0.38, P = 0.53), age (F1, 52.4 = 0.43, P = 0.51), hatch order (F1, 79.9 = 1.95, P = 0.17), nor Hg concentration (F1, 150.8 = 0.02, P = 0.88)
Different environmental stressors were associated with different time frames and biomarkers of physiological condition in egret and ibis chicks

Summary

Introduction

Environmental stressors, such as contaminants, prey availability, and adverse weather, can elicit strong physiological responses from wild birds in order to help them overcome short-term challenges. These responses can be harmful during the early stages of life if the response exceeds physiological norms [1,2,3]. Mercury (Hg) contamination and subsequent bioaccumulation in waterbirds is problematic in wetlands throughout the world. Inorganic Hg is converted into the toxic and bioaccumulative form methylmercury (MeHg) under biogeochemical conditions that are common in wetland ecosystems [6,7]. MeHg biomagnifies as it is transferred through the food chain [8,9,10]

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