Flightlessness and the Energetic Cost of Wing Molt in a Large Sea Duck

Abstract

Although the replacement of feathers apparently represents the major event of somatic production in the annual cycle of wild birds, knowledge about the energetics of molt has always been hampered by logistical and technical difficulties, which are exacerbated by the fact that birds are able to compensate behaviorally to buffer any variation in energy demand. During wing molt, sea ducks (Mergini) and other diving birds lose all of their wing feathers at once, leading to a period of temporary flightlessness of variable duration, a condition that considerably restricts their movements and increases the probability of predation. In the present study, we present the first results aimed at quantifying the duration of flightlessness, energy expenditure, and foraging effort during molt of a wing-propelled diving bird, the Common Eider (Somateria mollissima). Data loggers were implanted in the body cavity of 13 females to record heart rate and hydrostatic pressure (depth) every two seconds for a period of 220 days. Flight frequency and duration were assessed from elevated and constant heart rate, and the absence of flight was used to quantify the duration of flightlessness, which lasted, on average, 36 +/- 8 days (mean +/- SD). Using a period of four weeks before and four weeks after the flightless period, we found that dive depth (ranging from 1 to 2 m, on average) and daily diving time did not vary during the course of the study. Daily metabolic rate increased by 9%, and resting metabolic rate by 12% from the pre-molt period to the flightless period and remained high during the post-molt period. This study indicates that the energetic costs of replacing flight remiges in female eiders are substantial, although this is not associated with any change in foraging effort, which suggests that female Common Eiders lose mass during wing molt. Finally, estimates of energy savings associated with the total absence of flights during wing molt represent 6% of daily metabolic rate or 14% of resting metabolic rate. This finding contrasts with the classical view that little or no benefit is associated with a flightless condition. We suggest that such energy savings may have favored the evolution of temporary flightlessness in diving birds.

Leukocyte profiles indicate nutritional, but not moulting stress in a migratory shorebird, the Common Snipe (Gallinago gallinago)

“…As in many other bird species (e.g. Klaassen 1995;Guillemette et al 2007), the process of moult in the Common Snipe has been shown to be energetically costly. Young snipe were found to have lost more than 50% of their fat reserves during the postjuvenile moult (Minias et al 2010b), and depletion of endogenous fat was accompanied by a significant decrease in plasma concentrations of triglycerides during the advanced stage of moult (Podlaszczuk et al 2017).…”

“…Nutritional costs of moult are primarily associated with increased amino acid metabolism necessary for renewal of feathers, as well as with increased heat loss caused by reduced insulation (Lindström et al 1993;Klaassen 1995;Portugal et al 2007). Feather production results in a deposition of proteins that constitute up to 25% of lean body mass (Murphy and Taruscio 1995), and this process is associated with substantial increase of metabolic rate (Croxall 1982;Guillemette et al 2007). Also, flight-feather moult may impose additional energetic costs resulting from reduced flight performance (Swaddle and Witter 1997).…”

Migration characteristics of long-tailed ducks (Clangula hyemalis) from the western Canadian Arctic

“…Molt migration commenced when birds left the breeding location and ceased when birds arrived at the molt location. In the few instances when the molt location was not McKinley Bay in the year after marking, we identified the molt location as the area where birds were located for [28 days between mid-to late July and most of August and the distance between locations was \20 km (Guillemette et al 2007). Distances travelled during migratory periods were calculated by summing the distances between locations for the respective periods but should be considered minimum distances as ducks did not travel in a straight line between points.…”

Neither season nor sex affects the cost of terrestrial locomotion in a circumpolar diving duck: the common eider (Somateria mollissima)

“…At higher latitudes, seasonal variations in photoperiod elicit changes in avian physiology associated with energetically costly behaviours such as migration, egg-laying, incubation, wing moult and feather production (Piersma et al 2003;Guillemette et al 2007;Portugal and Guillemette 2011;. Furthermore, changes in climate may influence predation pressures, resource acquisition and thermoregulation, which may affect energy expenditure (Weathers and Sullivan 1993).…”