Does Water Temperature Affect the Timing and Duration of Remigial Moult in Sea Ducks? An Experimental Approach.

Anouck Viain,Magella Guillemette,Neil T Wright

doi:10.1371/journal.pone.0155253

Abstract

Aquatic birds have high cost of thermoregulation, especially during the moulting period, yet the effect of water temperature on the moulting strategy of aquatic birds has rarely been studied. Our general hypothesis is that energy savings associated with lower thermoregulation costs would be allocated to moulting processes. We predicted that aquatic birds moulting in warm water would have a higher level of body reserves, a faster growth rate of feathers, and an earlier remigial moult onset compared with birds moulting in cold water. We used the common eider (Somateria mollissima dresseri), a large sea duck, as the model species. Captive individuals were experimentally exposed to warm (18°C) and cold (8°C) water treatments during a three year period with individuals swapped between treatments. We found a similar feather growth rate for the two water temperature treatments and in contrast to our predictions, eiders exposed to warm water had a lower body mass and showed a delayed onset of remigial moult of approximately 7 days compared with those exposed to cold water. Our data indicate that body mass variations influence the timing of moult in unexpected ways and we suggest that it likely controls the occurrence of wing moult through a hormonal cascade. This study emphasizes the importance of improving our knowledge of the effects of water temperature on remigial moult of aquatic birds, to better assert the potential effects of global warming on their survival.

Highlights

The timing of major events in the annual cycle of birds, such as reproduction and migration, has recently been the subject of several studies, especially in the context of global climate change
We investigated the energy-conservation strategy hypothesis, which predicts that the energy conserved by lower thermoregulation costs in warm water will be re-allocated into higher body reserves, higher feather growth rate and an earlier remigial moult onset
The females exposed to cold water gained a mean of 307 g (16% of their initial body mass), whereas those exposed to warm water gained only 158 g (9%)

Summary

Introduction

The timing of major events in the annual cycle of birds, such as reproduction and migration, has recently been the subject of several studies, especially in the context of global climate change. The timing of moult is an important factor that can affect the body condition of birds as well as their future survival [1,2]. Many living organisms adjust their activities and physiological functions according to the photoperiod, which is a reliable cue for the timing of seasonal events. Photoperiod is used to initiate functions that trigger migration, reproduction, and moulting in birds [3,4,5]. In addition to the endogenously determined annual cycles of birds, several studies have shown that birds can use secondary non-photoperiodic cues, such as PLOS ONE | DOI:10.1371/journal.pone.0155253. In addition to the endogenously determined annual cycles of birds, several studies have shown that birds can use secondary non-photoperiodic cues, such as PLOS ONE | DOI:10.1371/journal.pone.0155253 May 13, 2016

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